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Pinus massoniana is an important industrial crop tree species commonly used for timber and wood pulp for papermaking, rosin, and turpentine. This study investigated the effects of exogenous calcium (Ca) on P. massoniana seedling growth, development, and various biological processes and revealed the underlying molecular mechanisms. The results showed that Ca deficiency led to severe inhibition of seedling growth and development, whereas adequate exogenous Ca markedly improved growth and development. Many physiological processes were regulated by exogenous Ca. The underlying mechanisms involved diverse Ca-influenced biological processes and metabolic pathways. Calcium deficiency inhibited or impaired these pathways and processes, whereas sufficient exogenous Ca improved and benefited these cellular events by regulating several related enzymes and proteins. High levels of exogenous Ca facilitated photosynthesis and material metabolism. Adequate exogenous Ca supply relieved oxidative stress that occurred at low Ca levels. Enhanced cell wall formation, consolidation, and cell division also played a role in exogenous Ca-improved P. massoniana seedling growth and development. Calcium ion homeostasis and Ca signal transduction-related gene expression were also activated at high exogenous Ca levels. Our study facilitates the elucidation of the potential regulatory role of Ca in P. massoniana physiology and biology and is of guiding significance in Pinaceae plant forestry. [Display omitted] • Ca deficiency led to severe inhibition of seedling growth and development. • Adequate exogenous Ca markedly improved growth and development. • High levels of exogenous Ca facilitated photosynthesis and material metabolism. • High exogenous Ca supply relieved oxidative stress and recovered redox homeostasis. • High exogenous Ca levels activated Ca signal transduction-related gene expression. [ABSTRACT FROM AUTHOR]

Shading can limit photosynthesis and plant growth. Understanding how phosphorus (P) application mitigates the effects of shading stress on morphology and physiology of mung beans (Vigna radiata L.) is of great significance for the establishment of efficient planting structures and optimizing P-use management. The effects of various light environments (non-shading stress, S0; low light stress, S1; severe shading stress, S2) on the growth of two mung bean cultivars (Xilv1 and Yulv1) and the role of P application (0 kg ha−1, P0; 90 kg ha−1, P1; 150 kg ha−1, P2) in such responses were investigated in a field experiment. Our results demonstrated that shading decreased the dry matter accumulation of mung bean markedly by limiting photosynthesis capacity and disrupting agronomic traits. For the leaf areas of the two cultivars, chlorophyll a +b, the net photosynthetic and electron transport rates were increased by 16.8%, 20.0%, 15.5%, and 12.5% under P1 treatment, and by 32.4%, 40.3%, 16.3% and 12.8% under P2 treatment, respectively, when compared to those for the non-fertilized plants under shading stress. These responses resulted in increased light capture and weak light utilization. Moreover, the activities of superoxide dismutase and peroxidase were enhanced by 20.9% and 43.7%, respectively; malondialdehyde and superoxide anion contents were reduced by 18.6% and 14.1%, respectively, under P application. These findings suggest that P application moderately mitigates the damage caused by shading stress and enhances tolerance by regulating mung bean growth. In addition, Xilv1 was more sensitive to P under shading stress than Yulv1. • P application enhanced light capture and utilization under shading stress. • P weakened MDA accumulation and O 2 − production in shaded leaves. • Sensitivity of the cultivars to P under abiotic stress was different. • Under 50% shade, mung bean exhibited higher P utilization efficiencies. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an important contributor to photosynthetic rate (Pn). However, during grain-filling stage in maize, some leaf N is remobilized to meet demands for grain protein accumulation rather than photosynthetic demands. Therefore, plants that can maintain a relatively high Pn during the N remobilization process would have the key to achieving both high grain yields (HGY) and high grain protein concentrations (HGPC). In this study, we investigated two high-yielding maize hybrids in photosynthetic apparatus and N allocation in a two-year field experiment. During grain filling, XY335 had a higher Pn and photosynthetic N-use efficiency than ZD958 had in the upper leaf, but not in the middle or lower leaves. In the upper leaf, the diameter and area of the bundle sheath (BS) were larger and the distance between bundle sheaths was greater in XY335 than in ZD958. XY335 had more bundle sheath cells (BSCs) and a larger BSC area, as well as a larger chloroplast area in the BSC, resulting in a higher total number and total area of chloroplasts in the BS. XY335 also had higher stomatal conductance (g s), intercellular CO 2 concentration, and N allocation to the thylakoids. No genotypic differences were found in mesophyll cell ultrastructure, N content and starch content in the three types of leaves. Therefore, a trifecta of higher g s , greater N allocation to thylakoids for photo-phosphorylation and electron transport, and more and larger chloroplasts promoting CO 2 assimilation in the BS confers a high Pn to simultaneously achieve HGY and high HGPC in maize. • How to stabilize Pn during N remobilization process is the key to synchronize HGY and HGPC. • The combination of high g s , NTH, more and larger chloroplasts of BSC confer high Pn. • Genotypic difference in Pn was not related to MS ultrastructure or starch conte. [ABSTRACT FROM AUTHOR]

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes. • Heat stress decreased leaf photosynthesis via non-stomatal factors. • Photosynthetic reductions were lower in plants pre-exposed to mild heat (priming). • Heat stress enhanced volatile emissions differently in primed and non-primed plants. • Volatile emissions recovered earlier in primed plants but later rose again. • Priming improves resistance and acclimation during subsequent severe heat stress. [ABSTRACT FROM AUTHOR]

Saccharina japonica (Laminariales, Phaeophyta) is a brown alga and the major component of algae beds on the northwest coast of the Pacific Ocean. Rubisco, the key enzyme of CO 2 fixation in photosynthesis, is inhibited by nonproductive binding of its substrate RuBP and other sugar phosphates. The inhibited Rubisco in eukaryotic phytoplankton of the red plastid lineage was reactivated by CbbXs, the red-type Rubisco activases, through the process of ATP-hydrolysis-powered remodeling. As well documented, CbbXs had two types of subunits encoded by the plastid or nuclear genome respectively. In this study, both proteins of S. japonica (SjCbbX-n and SjCbbX-p) were localized in the chloroplast illustrated by immuno-electron microscopy technique. GST pull-down detection verified SjCbbX-n could interact with SjCbbX-p. Two-dimensional electrophoresis-based Western blot analysis illustrated that the endogenous SjCbbXs could form heterohexamer in the ratio of 1:1. Activase activity assays showed that although both the recombinant proteins of SjCbbXs were functional, SjCbbX-n illustrated the significantly higher activase activity than SjCbbX-p. Notably, when the two proteins were mixed, the highest specific efficiencies of Rubisco were obtained. These results implied SjCbbX-n may be essential for Rubisco activation. Molecular evolutionary analysis of cbbx genes revealed that cbbx -n originated from the duplication of cbbx -p and then evolved independently under the positive selection pressure. This is the first report about the functional relationship between the two types of CbbXs in macroalge with the red-type Rubisco and provides useful information for revealing the mechanism of high photosynthetic efficiency of this important kelp. • Two subunits of Rubisco activase (SjCbbX-n and SjCbbX-p) were identified in Saccharina japonica. • Both SjCbbX-n and SjCbbX-p were localized in the chloroplast of S. japonica. • SjCbbX-n interacted with SjCbbX-p and formed heterohexamer in the chloroplast of S. japonica. • SjCbbX-n exhibited higher activase activity than SjCbbX-p. • Cbbx -n gene originated from the duplication of cbbx -p and then evolved independently. [ABSTRACT FROM AUTHOR]

Fluctuating light (FL) and drought stress usually occur concomitantly. However, whether drought stress affects photosynthetic performance under FL remains unknown. Here, we measured gas exchange, chlorophyll fluorescence, and P700 redox state under FL in drought-stressed tomato (Solanum lycopersicum) seedlings. Drought stress significantly delayed the induction kinetics of stomatal and mesophyll conductances after transition from low to high light and thus delayed photosynthetic induction under FL. Therefore, drought stress exacerbated the loss of carbon gain under FL. Furthermore, restriction of CO 2 fixation under drought stress aggravated the over-reduction of photosystem I (PSI) upon transition from low to high light. The resulting stronger FL-induced PSI photoinhibition significantly suppressed linear electron flow and PSI photoprotection. These results indicated that drought stress not only caused a larger loss of carbon gain under FL but also accelerated FL-induced photoinhibition of PSI. Furthermore, drought stress enhanced relative cyclic electron flow in FL, which partially compensated for restricted CO 2 fixation and thus favored PSI photoprotection under FL. To our knowledge, we here show new insight into how drought stress affects photosynthetic performance under FL. • We examine the effect of drought stress on dynamic photosynthesis in tomato. • Drought stress decreases mesophyll conductance during light induction. • Drought stress causes photosynthetic depression under fluctuating light. • Drought stress aggravates photoinhibition of photosystem I under fluctuating light. • Drought stress largely affects crop physiology under fluctuating light. [ABSTRACT FROM AUTHOR]

Extreme temperatures and droughts are considered as the two main factors that limit wheat growth and production. Although responses of wheat plants to heat and drought stress have been extensively investigated, little is known about the extent to which wheat plants can recover after stress relief. In this study, a winter wheat pot experiment was conducted to evaluate the growth, physiological activities, and yield formation responses of wheat to stress and recovery periods under heat stress (36 °C, daily maximum temperature), drought (45–55% of soil water holding capacity), and combined stress conditions. Heat and drought stress significantly reduced photosynthesis, leaf relative water content (LRWC), leaf water potential (LWP noon), and nitrogen metabolism enzyme activities and increased electrolyte leakage. These parameters showed significant interactions between heat and drought stress. Beneficial osmoregulation of membrane stability was observed in stressed plants because of the accumulation of proline and soluble sugars. Within a range of stresses, the abovementioned physiological processes of individual heat- and drought-stressed plants recovered to levels comparable to those of the control. The recovery capacities of the physiological traits decreased gradually with increasing stress duration, particularly under combined stress. The recovery of LWP noon and LRWC contributed to the improved photosynthetic performance after stress relief. The combined stress caused greater yield losses than individual heat and drought stress, which was mainly attributed to low levels of thousand grain weight (TGW), the number of grains per ear, and the grain filling rate. After stress relief, the recovery of proline content, glutamine synthetase activity, photosynthetic rate, and LRWC were closely associated with grain yield and thousand grain weight. Collectively, these findings contribute to a better understanding of the coordinated responses of winter wheat during the combined heat and drought stress and recovery periods. • Combined heat and drought stress is more detrimental to wheat than individual stress. • Most physiological processes of plants were reversible within a range of stress. • Recovery of physiological traits was closely related to wheat yield. [ABSTRACT FROM AUTHOR]

Iron nanoparticles (NPs) priming is known to affect the seed germination and seedling growth in many plants. However, whether it has an important role in stimulating the growth of perennial Qinghai-Tibet Plateau plants remains unclear. In this study, the effects of seed priming with different concentrations of nFe 2 O 3 and FeCl 3 (10, 50, 100, 500, and 1000 mg L−1) on seed germination, plant growth, photosystem, antioxidant enzyme activities, root morphology, and biomass distribution of Kobresia capillifolia were evaluated under laboratory conditions. The results showed that compared with treatment materials, concentration had more significant effects on K. capillifolia development. There was no significant impact on germination rate were discovered under all treatments, but decreased the seed mildew rate at 100 mg L−1 nFe 2 O 3. Compare with control, Fe-based priming significantly decreased root biomass. All Fe-based treatments increased rubisco activity of leaves, and significantly enhanced Pn at ranged from 10 to 100 mg L−1. Meanwhile, chlorophyll contents were decreased, the chloroplasts were swollen, and thylakoids were disorganized under all Fe treatments. Iron-based priming significantly enhanced SOD, POD, and CAT activities in Kobresia roots. In conclusion, the thick cuticle-covered seed coat of K. capillifolia postponed the penetration of FeNPs into seeds, so FeNPs priming had a weak impact on seed germination. The sustainable release of Fe ions from FeNPs and the uptake of Fe ions by roots affected the physiology, biochemistry and morphology of K. capillifolia. The findings of this study provide an in-depth understanding of how FeNPs impact the alpine meadow plant, K. capillifolia. [Display omitted] • Fe 2 O 3 NPs had no significant directly effect on Kobresia capillifolia seed germination. • High concentration Fe 2 O 3 NPs disrupted chloroplast structural and reduced photosynthesis. • Fe 2 O 3 NPs induced oxidative stress response in Kobresia capillifolia. • Fe 2 O 3 NPs had negatively affected roots more than leaves in Kobresia capillifolia. • Fe 2 O 3 NPs reduced biomass via inhibiting roots development and substance translocation. [ABSTRACT FROM AUTHOR]

Antibiotic pollution has become a global environmental pollution problem. Chlorophyll fluorescence is one of the most important indicators reflecting the degree to which plants are influenced by the environment. Ofloxacin (OFL) is a highly toxic antibiotic pollutant, and there are few reports on the effects of changes in OFL levels on tomato chlorophyll fluorescence parameters. In this study, we investigated the responses of tomato growth, photosynthetic activity and chlorophyll fluorescence kinetics to exogenous OFL exposure (as the concentrations of 0, 2.5, 5, 10 and 20 mg L−1). The results showed that lower concentrations of OFL (2.5 mg L−1) had little impact on tomato growth, while plant growth was inhibited with the OFL concentration increasing. At higher OFL concentrations (5, 10 and 20 mg L−1), chloroplasts ruptured, and chlorophyll became degraded, resulting in leaf etiolation. Furthermore, the photosynthetic and photochemical efficiency and electron transfer rate were significantly inhibited by OFL. Moreover, damage to the oxygen-evolving complex on the donor side of PSⅡ prevented electron transfer from QA to QB and led to photoinhibition. In conclusion, higher OFL concentration reduced photosynthesis by destroying the photosynthetic mechanism in tomato, resulting in tomato leaf etiolation and plant growth inhibition. • Low concentrations of OFL increased tomato seedings shoot growth. • The photosynthesis and chlorophyll fluorescence were significantly inhibited by OFL. • OFL treatment led to increased heat dissipation of light energy. • High dose of ofloxacin destroyed the chloroplast structure. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) regulate growth in many plants. Carbohydrates provide energy and carbon skeleton for cell growth. However, how CNTs influence plant carbohydrate metabolism remains largely unknown. For a comprehensive understanding the response of carbohydrate metabolism and accumulation in leaves of crabapple (Malus hupehensis Rehd) to single-walled carbon nanotubes (SWCNTs), the expression of key enzymes and genes involved in apple sugar metabolism was investigated. In this report, TEM showed that SWCNTs particles were absorbed in apple leaf. Foliar application of 10 and 20 mg/L SWCNTs promoted chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate. SWCNTs up-regulate the activity of aldose-6-phosphate reductase (A6PR), accompanied by increased concentration of photosynthetic assimilate‒sorbitol. However, the activities of sucrose phosphate synthase (SPS) and the accumulation of sucrose did not change significantly in SWCNTs-sprayed apple leaves compared with the control. In addition, the activities of photoassimilate degradation enzyme (sorbitol dehydrogenase, SDH; sucrose synthase, SUSY; neutral invertase, NINV) and hexose degradation enzyme (fructokinase, FRK; hexokinase, HK) were higher in SWCNTs-treated apple leaves than that in the control leaves. Quantitative real-time polymerase chain reaction (qRT‒PCR) results indicated that the expression of genes associated with sugar metabolism changed significantly after SWCNTs application. Taken together, we propose that spraying apple leaves with 10 and 20 mg/L SWCNTs can improve photosynthetic activity and accelerate carbohydrate metabolism in apple leaves. Our results provide insight into understanding the biological effects of CNTs in plants and are valuable for continued use of SWCNTs in agri-nanotechnology. • Foliar spraying of SWCNTs increases chlorophyll content and photosynthetic rate. • Foliar spraying of SWCNTs promotes the synthesis of photosynthetic assimilate. • Foliar spraying of SWCNTs up-regulates the activities of sugar degradation enzymes. [ABSTRACT FROM AUTHOR]

C 4 plants have the inherent capacity to concentrate atmospheric CO 2 in the vicinity of RuBisCo, thereby increasing carboxylation, and inhibiting photorespiration. Carbonic anhydrase (CA), the first enzyme of C 4 photosynthesis, converts atmospheric CO 2 to HCO 3 −, which is utilized by PEPC to produce C 4 acids. Bioengineering of C 4 traits into C 3 crops is an attractive strategy to increase photosynthesis and water use efficiency. In the present study, we isolated the PEPC gene from the C 4 plant Setaria italica and transferred it to C 3 rice. Overexpression of SiPEPC resulted in a 2-6-fold increment in PEPC enzyme activity in transgenic lines with respect to non-transformed control. Photosynthetic efficiency was enhanced in transformed plants, which was associated with increased ФPSII, ETR, lower NPQ, and higher chlorophyll accumulation. Water use efficiency was increased by 16–22% in PEPC transgenic rice lines. Increased PEPC activity enhanced quantum yield and carboxylation efficiency of PEPC transgenic lines. Transgenic plants exhibited higher light saturation photosynthesis rate and lower CO 2 compensation point, as compared to non-transformed control. An increase in net photosynthesis increased the yield by (23–28.9%) and biomass by (24.1–29%) in transgenic PEPC lines. Altogether, our findings indicate that overexpression of C 4- specific SiPEPC enzyme is able to enhance photosynthesis and related parameters in transgenic rice. • C4-specific PEPC gene from Setaria italica was transferred to indica rice variety IR64. • A significant increment in PEPC enzyme activity was found in transgenic rice. • The SiPEPC incorporation leads to enhancement in photosynthetic efficiency, WUE, RUE, ETR, and ФPSII in transgenic rice. • SiPEPC -transgenic rice plants exhibited an increase in grain yield and biomass. [ABSTRACT FROM AUTHOR]

Microplastics are a recent entrant in the list of environmental pollutants, exhibiting great diversity owing to different sizes, surface charges, and morphologies. The present study explores the impact of varied size, surface functionalization, and concentration of polystyrene microplastics (PS MP) on plants. For this study, Cicer seedlings were exposed to two different sizes of PS (1 μm and 12 μm) with three different surface functionalization (plain, carboxylated, and aminated) and at three distinct concentrations (10, 50, and 100 mg/L). The growth and photosynthetic parameters (like pigment content, Hill activity, etc.) along with oxidative stress marker (ROS) and anti-oxidant enzyme activities (like Superoxide dismutase, Catalase, and Peroxidase) were assessed. The results incline towards the idea that with increasing concentration of PS, there was a decline in the growth of the seedlings. There was also a dose-dependent increase in oxidative stress due to the suppression of the action of antioxidant enzymes. The effect was more prominent for 12 μm PS, perhaps due to its larger size and adherence to roots resulting in mechanical damage as deduced from MDA levels in the seedlings. Besides, MP with negative surface charge was comparatively less toxic than uncharged or positively charged PS of 1 μm. Overall, it can be concluded that the impact of MP on plants does not rely on individual characteristics of the particles alone, rather it is a concerted result of various determinants like size, charge, and concentration. [Display omitted] • Phytotoxicity of MPs varies with size, surface functionalization, and concentration. • MPs induce oxidative stress in Cicer. • Negatively charged MP is less toxic than MP with positive or no surface charge of 1 μm. • Larger-sized MP can induce more ROS resulting greater extent of root damage. • The activity of anti-oxidant enzymes suppressed at high concentrations of MPs. [ABSTRACT FROM AUTHOR]

Predictions for wheat grown under future climate conditions indicate a decline in grain protein concentration accompanied with an increase in yield due to increasing carbon dioxide concentrations. Currently, there is a lack of understanding as to the complete mechanism that governs the response of grain protein concentration (GPC) to elevated carbon dioxide (e[CO 2 ]). We investigated the GPC of 18 wheat genotypes from a doubled haploid wheat population and the two parental genotypes, Kukri and RAC0875. In addition, other nitrogen and biomass related traits were analysed to further elucidate which traits are connected with the decline in GPC. Wheat was grown under ambient and elevated [CO 2 ] in an environmentally controlled glasshouse. Plant nitrogen and biomass accumulation were measured at anthesis and maturity. We found that GPC declined under e[CO 2 ] and that the response of GPC to e[CO 2 ] was negatively correlated with nitrogen utilisation efficiency and harvest index. The extent that total biomass (anthesis), harvest index, photosynthesis, nitrogen utilisation and remobilisation efficiency, total nitrogen remobilisation and post-anthesis nitrogen uptake impacted GPC in response to e[CO 2 ] varied across genotype, suggesting that multiple mechanisms are responsible for GPC decline at e[CO 2 ] and that these mechanisms are effected differentially across genotypes. • GPC declines in some wheat genotypes under e[CO 2 ], but not all. • GPC response correlated negatively with both NUtE and HI response. • Nitrogen remobilisation contributes to maintaining GPC. • No single trait was involved in preventing GPC decline under e[CO 2 ]. [ABSTRACT FROM AUTHOR]

When a plant is exposed to heterogeneous light, the photosynthesis of unshaded leaves is often stimulated to compensate for the decline in photosynthesis of shaded leaves, i.e., photosynthetic compensation. However, a decline of photosynthesis in unshaded leaves, which means an impairment of photosynthetic compensation, has also been widely reported. Herein, two cultivars of maize (Zea mays L.), 'Rongyu1210' (RY) and 'Zhongdan808' (ZD), were studied comparatively. Both cultivars performed evident photosynthetic compensation under heterogeneous light (HL) as the light phase begins (8:30 a.m.). However, as the light phase continues (10:30 a.m.), an impairment of photosynthetic compensation took place in HL-treated ZD, but not in HL-treated RY. For both cultivars, nitrogen content of unshaded leaves was higher under HL, indicating a preferential nitrogen distribution towards unshaded leaves. This is related to the photosynthetic compensation but not the cause of the impairment. In addition, no obvious difference was found in the response of photosynthates (sucrose and starch) to HL between cultivars at 8:30 a.m. However, at 10:30 a.m., the content of photosynthates decreased significantly in unshaded leaves of HL-treated RY, along with increased abundances of both sucrose transporters (SUTs) and H+-ATPase (EC 7.1.2.1). In contrast, it increased along with decreased abundances of SUTs and H+-ATPase in HL-treated ZD. These results suggest that the photosynthetic compensation is impaired when photosynthates export of unshaded leaves is restricted. This suggestion is further confirmed by the results of 13C labeling and dry weight detection on young leaves as 'sink'. • Photosynthetic compensation is a common phenomenon as the light phase begins. • An impairment of photosynthetic compensation may happen as the light phase continues. • Photosynthetic compensation is impaired when photosynthates export is restricted. [ABSTRACT FROM AUTHOR]

The vital signaling molecule 5-Aminolevulinic acid (ALA) plays critical roles in signal transduction and biological modulation under abiotic stresses. In this study, we explored the effects of exogenous ALA on low-light (LL) stress-induced photosynthesis and antioxidant system damage in tall fescue (Festuca arundinacea Schreb.) seedlings. LL stress decreased morphological index values and chlorophyll contents, while also reduced net photosynthetic rate (Pn) and the maximum quantum yield of photosystem II photochemistry (F v / F m). Notably, these restrictions were substantially alleviated by exogenous ALA. Moreover, the contents of chlorophyll and its synthetic precursors were significantly increased after ALA treatment. Meanwhile, ALA observably enhanced expression level of FaCHLG , FaHEMA , FaPOR , and FaCAO , which encode the chlorophyll precursors biosynthesis enzymes. Exogenous ALA repaired the damage to the chloroplast ultrastructure caused by LL stress and promoted the formation of ordered thylakoids and grana lamella. ALA also improved Rubisco activity and expression level of the photosynthetic enzyme genes FaRuBP , FaPRK , and FaGADPH. Additionally, application of exogenous ALA decreased relative electrolytic leakage and the accumulation of malondialdehyde (MDA), hydrogen peroxide (H 2 O 2), and superoxide radicals (O 2 ∙-), and increased the gene expression levels and activity of antioxidant enzymes. The ratios of ascorbic acid (AsA) to dehydroascorbic acid (DHA) and reduced glutathione (GSH) to oxidized glutathione (GSSG) were also increased significantly by application of ALA. Furthermore, all responses could be reversed by treatment with levulinic acid (LA). Thus, these results indicated that ALA protects tall fescue from LL stress through scavenging ROS, improving photosynthetic enzyme activity levels, increasing photosynthetic pigments contents, repairing chloroplast damage, and enhancing the photosynthesis rate. • ALA repaired the damage to the chloroplast ultrastructure caused by low-light (LL) stress. • ALA activated enzymic antioxidant system and AsA-GSH cycle to remove excess ROS. • ALA promoted the chlorophyll biosynthesis pathway to enhancing photosynthetic pigment contents. • ALA enhanced photosynthetic performance to keep a high photosynthesis level under LL stress. [ABSTRACT FROM AUTHOR]

Nanotechnologies provide a great platform for researching nanoparticles effects on living organisms including plants. This work shows the stimulating effect of seed priming with gold nanoparticles (AuNPs) on photosynthetic apparatus of Triticum aestivum seedlings. It was found using inductively coupled plasma-atomic emission and mass spectrometry that AuNPs (the average diameter of 15.3 nm, concentration of 20 μg ml−1) penetrated into the seeds, but were not found in seedling leaves. Ultrastructural changes in chloroplasts were found using transmission electron microscopy in plants grown from treated seeds: increases in the size of plastids, starch grains, grana in chloroplasts, and the number of thylakoids in grana. The intensity of photosynthesis, the content of chlorophylls, and the portion of unsaturated fatty acids in the composition of total leaf lipids were increased in treated AuNPs plants. This study demonstrates that revealed changes determined the increased tolerance of wheat to low temperature. The adaptive significance of these changes, possible mechanisms of the AuNPs effects on plants and future perspectives of study are discussed. This is the first report showing nanopriming with AuNPs as a new method to study the mechanisms of stress tolerance. • Priming with AuNPs is a trigger of wheat chloroplasts ultrastructural reorganization. • Seed priming with AuNPs increases photosynthesis and chlorophylls content of wheat. • Fatty acids composition in wheat leaves changed after AuNPs treatment. • Seed priming with AuNPs increases cold tolerance of wheat plants. [ABSTRACT FROM AUTHOR]

Macrotyloma uniflorum (horse gram) is considered an under-utilized legume crop despite its nutritional and medicinal values. In India, it has wide acceptance among farming communities. This investigation emphasized on the possible application of two endosymbionts (Bacillus sp. AS03 and Rhizobium sp. AS05) of horse gram cultivated on Cr (VI)-contaminated soil. The photosynthetic performance (PIφ) of Cr treated plants co-inoculated with AS03 and AS05 was significantly improved compared with non-inoculated Cr treated plants based on photosynthetic yield, which was evidenced from the rise in the fluorescence at I–P transient and rate of photosynthesis (pN), indicating synergistic action between plant and bacteria (AS03 and AS05). The smooth electron transport from PS II to PS I was achieved in the Cr stressed plants inoculated with both the bacterial strains. The detrimental effects of Cr toxicity on the root tips were also minimized with bioinoculation as revealed from mitotic index. Plants with dual inoculation of AS03 and AS05 had significantly lesser chromosomal aberration in the roots. Dual inoculation biochar or seed inoculation have beneficial impact on the plant photosynthetic performance along with improved growth of roots in plants treated with Cr (VI). The results of the current work suggest the possitive effect of dual inoculation of Cr tolerant endosymbionts, Bacillus sp. (AS03) and nodulating Rhizobium sp. (AS05), in reducing cytological as well as physiological stress of plants in Cr (VI) contaminated soil. [Display omitted] • Endosymbiotic Bacteria drops Abnormality Index in Macrotyloma under Cr (IV) stress. • Dual inoculation increased photosynthetic performance of Macrotyloma. • Chlorophyll fluorescence parameters showed synergistic effect of dual inoculation. [ABSTRACT FROM AUTHOR]

Sugar synthesis from photosynthesis and its utilization through sugar metabolism jointly determine leaf sugar content, and in contrast, excess sugar represses leaf photosynthesis. Although plant photosynthesis is affected by leaf sugar metabolism, the relationship between sugar metabolism and photosynthetic capacity of different grape genotypes remains unclear. In this study, two grape (Vitis vinifera L.) genotypes 'Riesling' (RI, high sugar content in leaf) and 'Petit Manseng' (PM, low sugar content in leaf) were used to evaluate the relationship between sugar metabolism and photosynthesis. Sugar content, chlorophyll content, photosynthetic parameters, enzyme activity, and gene expression related to sucrose metabolism in leaves were measured, and the correlations between photosynthesis and sugar metabolism were assessed. The contents of sucrose and glucose were significantly higher in RI leaves than in PM leaves, while the fructose content pattern was reversed. Cell wall invertase activity for sucrose hydrolysis and the transcript levels of VvCWINV , VvHT s, VvTMT1 , VvFK s, and VvHXK2 were also higher in RI leaves than in PM leaves, whereas that of VvHXK1 mediating glucose phosphorylation, was lower in RI leaves than in PM leaves. Net photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll content were lower in RI leaves than in PM leaves and negatively correlated with glucose content, and the transcript levels of VvCWINV , VvHT s, VvTMT1 , and VvHXK2. In conclusion, this study indicates that leaf sugar metabolism and transport are related to photosynthesis in Vitis vinifera L., which provides a theoretical basis for improving grape photosynthesis. • Inter-varietal variation in sugar metabolism corresponds to sugar content variation. • Leaf sugar transport is induced in response to sugar accumulation. • Leaf sugar accumulation trends modifying photosynthesis. [ABSTRACT FROM AUTHOR]

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S0) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg−1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26–11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26–11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S0, 100 or 200 mg S kg−1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S0 also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O 2 •−) and H 2 O 2 , hydrogen peroxide, in As affected plants. In general, S0 at 200 mg kg−1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S0 at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H 2 S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H 2 S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S0 as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils. • The arsenic (As) toxicity decreased the growth and development in Brassica napus. • As toxicity enhanced As uptake and generation of reactive oxygen species (ROS) thus decreases photosynthesis.. • Supplementation of sulfur (S) alleviates As toxicity through decreased production of ROS. • S mitigates oxidative damage by enhanced antioxidants, metal chelators and non-protein thiols. • S enhanced endogenous hydrogen sulfide (H 2 S) content that imparts defense against As toxicity. [ABSTRACT FROM AUTHOR]

In plants, abiotic stressors are frequently encountered during growth and development. To counteract these challenges, zinc finger proteins play a critical role as transcriptional regulators. The EgrZFP6 gene, which codes for a zinc finger protein of the C2H2 type, was shown to be considerably elevated in the leaves of Eucalyptus grandis seedlings in the current study when they were subjected to a variety of abiotic stimuli, including heat, salinity, cold, and drought. Analysis conducted later showed that in EgrZFP6 transgenic Arabidopsis thaliana , EgrZFP6 was essential for causing hyponastic leaves and controlling the stress response. Furthermore, the transgenic plants showed elevated levels of reactive oxygen species (ROS), such as superoxide and hydrogen peroxide (H 2 O 2). Additionally, in EgrZFP6 -overexpressing plants, transcriptome sequencing analysis demonstrated a considerable downregulation of many genes involved in photosynthesis, decreasing electron transport efficiency and perhaps promoting the buildup of ROS. Auxin levels were higher and auxin signal transduction was compromised in the transgenic plants. Stress-related genes were also upregulated in Arabidopsis as a result of EgrZFP6 overexpression. It is hypothesized that EgrZFP6 can downregulate photosynthesis, which would cause the production of ROS in chloroplasts. As a result, this protein may alter plant stress responses and leaf morphology via a retrograde mechanism driven by ROS. These results highlight the significance of zinc finger proteins in this sophisticated process and advance our understanding of the complex link between gene regulation, ROS signaling, and plant stress responses. • Overexpressing EgrZFP6 leads to enhanced levels of reactive oxygen species. • EgrZFP6-overexpressing plants elevate auxin levels and hinder auxin signaling. • EgrZFP6 influence leaf morphology and stress responses via a retrograde pathway. [ABSTRACT FROM AUTHOR]

Grafting is applied in Solanaceae to improve growth and quality traits. However, grafting potato onto a wooden goji rootstock is rare. Our study introduces a novel distant grafting technique to investigate potato scion responses, specifically regarding photosynthetic and tuber nutritional quality. The physiological and transcriptomic findings reveal an increase in photosynthesis ratio and carbon fixation in potato leaves after 45 days of grafting due to the upregulation of pivotal genes (PsbA , PPC1 , rbcl, and GAPDH). After 95 days of long-term growth, the leaf redox balance was maintained with intensified chlorophyll synthesis, facilitated by the enrichment of crucial genes (GUN4 , CHLH , CHLP , CAO) and several light-harvesting proteins (Lhca and Lhcb) in potato leaves. The tubers of grafted plants showed a 6.5% increase in crude protein, 51% in anthocyanin, and lower carbohydrate content. Goji altered the expression of tubers genes involved in assimilatory sulfate reduction, which subsequently affects cysteine-methionine biosynthesis. Furthermore, the tuber transcriptome shows ABA signaling and transcription factors regulate the expression of key biosynthetic genes involved in inducing the secondary metabolites, such as scopoletin and anthocyanin accumulation, which are primary polyphenols in goji. Our innovative grafting approach offers valuable insights into the interactions between woody and herbaceous plants for developing future strategies to modulate growth efficiency and tuber quality in the face of climate challenges and to meet the demand for nutritious food. [Display omitted] • Goji rootstock enhances chlorophyll, PSII efficiency and delay senescence. • Harvested tubers had higher anthocyanin, protein, and a lower carbohydrate content. • Sulfur assimilation is incorporated into amino acid synthesis and enzymes activity. • ABA signaling in tubers activates TFs that regulate quality and dormancy. • Upregulation of 3RT and BAHD- 5AT enhanced the anthocyanins biosynthesis. [ABSTRACT FROM AUTHOR]

Soil salinization effects plant photosynthesis in a number of global ecosystems. In this study, photosynthetic and physiological parameters were used to elucidate the impacts of saline-alkaline stress on Cyperus esculentus L. (C. esculentus) seedling photosynthesis. The results demonstrate that salt stress, alkali stress and mixed salt and alkali stress treatments all have similar bell-shaped influences on photosynthesis. At low concentrations (0−100 mmol L−1), saline-alkaline stress promoted net photosynthetic rate, transpiration rate and water use efficiency in C. esculentus. However, as the treatments increased in intensity (100−200 mmol L−1), plant photosynthetic parameters began to decline. We interpreted this as the capacity of C. esculentus to improve osmoregulatory capacity in low saline-alkaline stress treatments by accumulating photosynthetic pigment, proline and malondialdehyde to counterbalance the induced stress – an adaptive mechanism that failed once concentrations reached a critical threshold (100 mmol L−1). Stomatal conductance, maximum photosynthetic rate and actual photosynthetic rate all decreased with increasing concentration of the stress treatments, and intercellular carbon dioxide showed a decreasing and then increasing trend. These results indicated that when the saline-alkaline stress concentrations were low, C. esculentus seedlings showed obvious adaptive ability, but when the concentration increased further, the physiological processes of C. esculentus seedlings were significantly affected, with an obvious decrease in photosynthetic efficiency. This study provides a new understanding of the photosynthetic adaptation strategies of C. esculentus seedlings to varying concentrations of saline-alkaline stress. • Photosynthesis in C. esculentus did not differ under saline-alkaline stress. • At low levels, C. esculentus adapted photosynthetically, showing salt tolerance. • Stomatal limitation is the dominant factor of low stress in C. esculentus seedlings. • High concentration impairs C. esculentus photosynthesis mechanisms. [ABSTRACT FROM AUTHOR]

Methyl viologen (MV), also known as paraquat, is a widely used herbicide but has also been reported as highly toxic to different life forms. The mode of its operation is related to superoxide radical (O 2 .-) production and consequent oxidative damage. However, besides the damage to key macromolecules, reactive oxygen species (ROS; to which O 2 .- belongs) are also known as regulators of numerous ion transport systems located at cellular membranes. In this study, we used MV as a tool to probe the role of O 2 .- in regulating membrane-transport activity and systemic acquired tolerance in halophytic Chenopodium quinoa and glycophytic spinach plants. Both plant species showed growth reduction in terms of reduced shoot length, lower shoot fresh and dry weight, photosynthesis rate, and chlorophyll contents; however, quinoa showed less reduction in growth compared with spinach. This whole plant response was further examined by measuring the ion concentration, gene expression of ion transporters, activation of antioxidants, and osmolyte accumulation. We observed that at the mechanistic level, the differences in growth in response to MV were conferred by at least four complementary physiological mechanisms: (1) higher K+ loss from spinach leaves resulted from higher expression of MV-induced plasma membrane-based depolarization-activated K+ efflux GORK channel, (2) higher activation of high-affinity K+ uptake transporter HAK5 in quinoa, (3) higher antioxidant production and osmolyte accumulation in quinoa as compared with spinach, and (4) maintaining a higher rate of photosynthesis due to higher chlorophyll contents, and efficiency of photosystem II and reduced ROS and MDA contents. Obtained results also showed that MV induced O 2 .- significantly reduced N contents in both species but with more pronounced effects in glycophytic spinach. Taken together this study has shown the role of O 2 .- in regulating membrane ion transport and N metabolism in the leaves of halophyte vs. glycophyte in the context of oxidative stress tolerance. • Halophytic Chenopodium quinoa and glycophytic spinach plants were studied for their sensitivity to superoxide radical (O 2 .-) stress. • O 2 .- regulates membrane ion transport and N metabolism in leaf mesophyll. • Superior oxidative stress tolerance of quinoa was attributed to higher antioxidant production, osmolyte accumulation, and better K+ homeostasis. • Oxidative stress tolerance also explains a superior salinity stress tolerance of quinoa. [ABSTRACT FROM AUTHOR]

In the context of climate change, the impact of root-zone warming (RW) on crop nutrient absorption and utilization has emerged as a significant concern that cannot be overlooked. Nitrogen (N) is an essential element for crop growth and development, particularly under stress. The comprehensive effect and relationship between RW and N level remains unclear. The objective of this experiment was to investigate the impact of RW on root-shoot growth and photosynthetic physiological characteristics of maize seedlings under varying N levels. The results demonstrated that optimal RW was beneficial to the growth of maize, while excessive root-zone temperature (RT) significantly impeded N uptake in maize. Under low N treatment, the proportion of N distribution in roots increased, and the root surface area increased by 41 %. Furthermore, under low N levels, the decline in root vitality and the increase in root MDA caused by high RT were mitigated, resulting in an enhancement of the root's ability to cope with stress. For the above-ground part, under the double stress of high RT and low N, the shoot N concentration, leaf nitrate reductase, leaf glutamine synthase, chlorophyll content, net photosynthetic rate and shoot dry matter accumulation decreased by 86 %, 60 %, 35 %, 53 %, 64 % and 59 %, respectively. It can be reasonably concluded that reasonable N management is an important method to effectively reduce the impact of high RT stress. • Root zone temperature and nitrogen significantly affected the growth and development of maize seedlings. • Root zone temperature and nitrogen had obvious interactions. • Low nitrogen increased the ability of roots to cope with high temperature stress in root zone. • The growth of the aboveground part was the worst under the dual stress of low nitrogen and high root-zone temperature. • The change of root absorption capacity and nitrogen distribution is an important reason for the interaction. [ABSTRACT FROM AUTHOR]

Changes of membrane lipid composition contribute to plant adaptation to various abiotic stresses. Here, a comparative study was undertaken to investigate the mechanisms of how lipid alteration affects plant growth and development under nitrogen (N) deficiency. Two wheat cultivars: the N deficiency-tolerant cultivar Xiaoyan 6 (XY) and the N deficiency-sensitive cultivar Aikang 58 (AK) were used to test if the high N-deficiency tolerance was related with lipid metabolism. The results showed that N deficiency inhibited the morpho-physiological parameters in both XY and AK cultivars, which showed a significant decrease in biomass, N content, photosynthetic efficiency, and lipid contents. However, these decreases were more pronounced in AK than XY. In addition, XY showed a notable increase in fatty acid unsaturation, relatively well-maintained chloroplast ultrastructure, and minimized damage of lipid peroxidation and enhanced PSII activity under N-deficient condition, as compared with AK. Transcription levels of many genes involved in lipid biosynthesis and fatty acid desaturation were up-regulated in response to N deficiency in two wheat cultivars, while the expressions were much higher in XY than AK under N deficiency. These results highlight the importance of alterations in lipid metabolism in N deficiency tolerance in wheat. High levels of lipid content and unsaturated fatty acids maintained the membrane structure and function, contributing to high photosynthesis and antioxidant capacities, thereby improved the tolerance to N deficiency. • Tolerant cultivar maintains integrated membrane structure under N deficiency. • Fatty acid unsaturation is essential for maintaining membrane function. • Alteration in lipid metabolism contributes to high N deficiency tolerant. [ABSTRACT FROM AUTHOR]

As an important warm-season turfgrass species, bermudagrass (Cynodon dactylon L.) flourishes in warm areas around the world due to the existence of the C4 photosynthetic pathway. However, how C4 photosynthesis operates in bermudagrass leaves is still poorly understood. In this study, we performed single-cell RNA-sequencing on 5296 cells from bermudagrass leaf blades. Eight cell clusters corresponding to mesophyll, bundle sheath, epidermis and vascular bundle cells were successfully identified using known cell marker genes. Expression profiling indicated that genes encoding NADP-dependent malic enzymes (NADP-MEs) were highly expressed in bundle sheath cells, whereas NAD-ME genes were weakly expressed in all cell types, suggesting C4 photosynthesis of bermudagrass leaf blades might be NADP-ME type rather than NAD-ME type. The results also indicated that starch synthesis-related genes showed preferential expression in bundle sheath cells, whereas starch degradation-related genes were highly expressed in mesophyll cells, which agrees with the observed accumulation of starch-filled chloroplasts in bundle sheath cells. Gene co-expression analysis further revealed that different families of transcription factors were co-expressed with multiple C4 photosynthesis-related genes, suggesting a complex transcription regulatory network of C4 photosynthesis might exist in bermudagrass leaf blades. These findings collectively provided new insights into the cell-specific expression patterns and transcriptional regulation of photosynthetic genes in bermudagrass. • 5296 protoplast cells from bermudagrass leaf blades were analyzed by single-cell RNA-sequencing. • Eight cell clusters representing mesophyll, bundle sheath, epidermis and vascular bundle cells were identified. • NADP-ME genes were highly expressed in bundle sheath cells, whereas NAD-ME genes were weakly expressed in all cells. • Starch synthesis- and degradation-related genes showed preferential expression in different types of cells. • Different families of transcription factors were co-expressed with different photosynthesis-related genes. [ABSTRACT FROM AUTHOR]

The primary goal of this research is to investigate the mitigating effect of silicon (Si; 2 mM) on the growth of tomato seedlings under vanadium (V; 40 mg) stress. V stress caused higher V uptake in leaf, and enhanced concentration of leaf anthocyanin, H 2 O 2 , O 2 •−, and MDA, but a decreased in plant biomass, root architecture system, leaf pigments content, mineral elements, and Fv/Fm (PSII maximum efficiency). Si application increased the concentrations of crucial antioxidant molecules such as AsA and GSH, as well as the action of key antioxidant enzymes comprising APX, GR, DHAR, and MDHAR. Importantly, oxidative damage was remarkably alleviated by upregulation of these antioxidant enzymes genes. Moreover, Si application enhanced the accumulation of secondary metabolites as well as the expression their related-genes, and these secondary metabolites may restricted the excessive accumulation of H 2 O 2. In addition, Si rescued tomato plants against the damaging effects of MG by boosting the Gly enzymes activity. The results confirmed that spraying Si to plants might diminish the V accessibility to plants, along with promotion of V stress resistance. [Display omitted] • Silicon increased leaf photosynthesis performance of tomato seedling. • Silicon inhibited vanadium accumulation from root to shoot. • Silicon modified root structure and improved ion homeostasis in tomato seedlings. • Silicon up-regulated the antioxidant enzymes system of tomato seedlings. [ABSTRACT FROM AUTHOR]

Arsenic (As) is a metalloid pollutant that is extensively distributed in the biosphere. As is among the most prevalent and toxic elements in the environment; it induces adverse effects even at low concentrations. Due to its toxic nature and bioavailability, the presence of As in soil and water has prompted numerous agricultural, environmental, and health concerns. As accumulation is detrimental to plant growth, development, and productivity. Toxicity of As to plants is a function of As speciation, plant species, and soil properties. As inhibits root proliferation and reduces leaf number. It is associated with defoliation, reduced biomass, nutrient uptake, and photosynthesis, chlorophyll degradation, generation of reactive oxygen species, membrane damage, electrolyte leakage, lipid peroxidation and genotoxicity. Plants respond to As stress by upregulating genes involved in detoxification. Different species have adopted avoidance and tolerance responses for As detoxification. Plants also activate phytohormonal signaling to mitigate the stressful impacts of As. This review addresses As speciation, uptake, and accumulation by plants. It describes plant morpho-physiological, biochemical, and molecular changes and how phytohormones respond to As stress. The review closes with a discussion of omic approaches for alleviating As toxicity in plants. • Arsenic, a carcinogenic metalloid, enters plants through phosphate transporters (PHT) and aquaglycoporins. • Arsenic uptake in plants disturbs metabolism, resulting in structural, physiological, and biochemical problems. • Arsenic toxicity results in oxidative stress by forming reactive oxygen species (ROS). • Arsenic toxicity activates enzymatic and non-enzymatic antioxidants in plants to neutralize it. • The sustainable agriculture approach involves Transcriptomics, proteomics, and metabolomics responses. [ABSTRACT FROM AUTHOR]

The study evaluated the effects of treating irrigation water with a coaxial flow variator (CFV) on the morpho-physiology of pot-cultivated test species, including cucumber (Cucumis sativus, CU), lettuce (Lactuca sativa , LE), and sorghum (Sorghum vulgare , SO), in early stages of growth. CFV caused a lower oxidation reduction potential (ORP), increased pH and flow resistance and inductance. It induced changes in the absorbance characteristics of water in specific spectral regions, likely associated with greater stretching and reduced bending vibrations compared to untreated water. While assimilation rate and photosynthetic efficiency were not significantly affected at 60 days after sowing, treated water increased the stomatal conductance to water vapour gsw (+79%) and the electron transport rate ETR (+10%) in CU, as well as the non-photochemical quenching NPQ (+33%) in SO. Treated water also reduced leaf temperature in all species (−0.86 °C on average). This translated into improved plant biomass (leaves: +34%; roots: +140%) and reduced leaf-to-root biomass ratio (−42%) in SO, allowing both faster aerial growth and soil colonization, which can be exploited to improve plant tolerance against abiotic stresses. In the C3 species CU and LE, plant biomass was instead reduced, although significantly in LE only, while the leaf-to-root biomass ratio was generally enhanced, a result likely profitable in the cultivation of leafy vegetables. This is a preliminary trial on the effects of functionalized water and much remains to be investigated in other physiological processes, plant species, and growth stages for the full exploitation of this water treatment in agronomy. • Treatment with coaxial flow variator (CFV) modifies some traits of irrigation water • CFV lowered oxidation reduction potential, increased pH, resistance and inductance • Specific photosynthetic parameters were improved, depending on plant species • Improved plant weight and reduced leaf-to-root biomass ratio in sorghum • Reduced plant biomass and higher leaf-to-root biomass ratio in cucumber and lettuce [ABSTRACT FROM AUTHOR]

Elevated CO 2 concentrations may inhibit photosynthesis due to nitrogen deficiency, but legumes may be able to overcome this limitation and continue to grow. Our study confirms this conjecture well. First, we placed the two-year-old potted saplings of Ormosia hosiei (O. hosiei) (a leguminous tree species) in the open-top chamber (OTC) with three CO 2 concentrations of 400 (CK), 600 (E1), and 800 μmol·mol−1 (E2) to simulate the elevated CO 2 concentration environment. After 146 days, the light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (AQE), and dark respiration rate (Rd) of O. hosiei were increased under increasing CO 2 concentration and obtain the maximum ribulose diphosphate (RuBP) carboxylation rate (V c max) and RuBP regenerated photosynthetic electron transfer rate (J max) were also significantly increased under E2 treatment (P < 0.05). This results in a significant increase of the maximum assimilation rate (A max) under elevated CO 2 concentrations. Sucrose phosphate synthase (SPS) activity in sucrose metabolism increased in the leaves, more soluble sugars, starches, and sucrose was produced, but sucrose content only in leaves increased at E2, and more carbon flows to the roots. The activity of the NH 4 + assimilating enzymes glutamine synthetase (GS), glutamate synthetase (GOGAT), and glutamate dehydrogenase (GDH) in the leaves of O. hosiei increases under elevated CO 2 concentrations to promote nitrogen synthesis that reduces the content of ammonium nitrogen and increases the content of nitrate nitrogen. In addition, under E1 conditions, sucrose synthase (SS), direction of synthesis activity was highest and sucrose invertase (INV) activity was lowest, this means that the balance of C and N metabolism is maintained. While under E2 conditions SS activity decreased and INV activity increased, this increased C/N and nitrogen use efficiency. So, the elevated CO 2 concentration promotes the accumulation of O. hosiei biomass, especially in the aboveground part, but did not have a significant effect on the accumulation of root biomass. This means that O. hosiei is able to cope under the elevated CO 2 concentration without showing photosynthetic adaptation during the experimental period. • The legume of O.hoeisi did not show photosynthetic adaptation under elevated CO 2 concentration. • In elevated CO 2 environment, O.horeisi 's strong C input promoted nodule nitrogen fixation. • Elevated CO 2 concentration was beneficial to the biomass accumulation of O.houeisi , especially the aboveground part. [ABSTRACT FROM AUTHOR]

Chloride (Cl−) is traditionally categorized as an antagonist of nitrate (NO 3 −) because Cl− hinders plant NO 3 − transport and accumulation. However, we have recently defined Cl− as a beneficial macronutrient for higher plants, due to specific functions that lead to more efficient use of water, nitrogen (N) and CO 2 under optimal N and water supply. When accumulated in leaves at macronutrient levels, Cl− promotes growth through osmotic, physiological, metabolic, anatomical and cellular changes that improve plant performance under optimal NO 3 − nutrition. Nitrate over-fertilization in agriculture can adversely affect crop yield and nature, while its deficiency limits plant growth. To study the relationship between Cl− nutrition and NO 3 − availability, we have characterized different physiological responses such as growth and yield, N-use efficiency, water status, photosynthesis, leaf anatomy, pigments and antioxidants in tomato plants treated with or without 5 mM Cl− salts and increasing NO 3 − treatments (3–15 mM). First, we have demonstrated that 5 mM Cl− application can reduce the use of NO 3 − in the nutrient solution by up to half without detriment to plant growth and yield in tomato and other horticultural plants. Second, Cl− application reduced stress symptoms and improved plant growth under low-NO 3 − conditions. The Cl−-dependent resistance to low-N stress resulted from: more efficient use of the available NO 3 −; improved plant osmotic and water status regulation; improved stomatal conductance and photosynthetic rate; and better antioxidant response. We proposed that beneficial Cl− levels increase the crop ability to grow better with lower NO 3 − requirements and withstand N deficiency, promoting a more sustainable and resilient agriculture. • This study focuses on the study of the physiological responses of plants to chloride and nitrate nutrition. • Chloride can partially replace nitrate application maintaining growth and yield in several horticultural plants. • Symptoms of low nitrogen stress are alleviated by chloride nutrition at macronutrient levels. • The better chloride-dependent water status sustains plant growth and photosynthesis under low nitrogen stress conditions. [ABSTRACT FROM AUTHOR]

The escalating influence of environmental changes has heightened the physiological challenges faced by plants, with drought stress increasingly recognized as a critical global issue significantly impeding affecting the crop productivity. This study investigates the effectiveness of metal nano particles such as zinc oxide nanoparticles (ZnO NPs) and silver nanoparticles (Ag NPs) in mitigating drought stress in Solanum lycopersicum. The foliar application of ZnO NPs (500 ppm) and/or Ag NPs (500 ppm), individually or in combination, significantly alleviated drought stress-induced. This mitigation was evidenced by enhanced antioxidant enzymes activity viz., catalase (64%), peroxidase (76%), superoxide dismutase (78%), chlorophyll content (31%) & photosynthesis (37%), and protein levels (15%). Furthermore, ZnO NPs and Ag NPs effectively mitigated oxidative stress and lipid peroxidation, as evidence by reduced accumulation of malondialdehyde (11%). Remarkably, the combined application of ZnO NPs and Ag NPs expedited the water-splitting capacity and facilitated electron exchange through redox reactions under drought stress. Consequently, these enhancements positively influenced the morpho-physiological characteristics such as height (28%), fresh weight (31%), dry weight (29%) and net photosynthetic rate (37%) of S. lycopersicum. These findings underscore the promising potential of metal NPs, such as ZnO NPs and Ag NPs, in mitigating drought stress, offering valuable insights for sustainable crop production amidst evolving environmental challenges. [Display omitted] • Anthropogenic climate change causes drought stress, which hinders crop productivity and global dispersion. • Study evaluates zinc oxide nanoparticles (ZnO NPs) and silver nanoparticles (Ag NPs) for drought stress alleviation in Solanum lycopersicum. • Foliar application of ZnO NPs and/or Ag NPs significantly mitigates drought stress in tomato plants by improving antioxidant enzymes activity and photosynthetic attributes. • Combined ZnO NPs and Ag NPs application improves water-splitting capacity, positively impacting plant characteristics. [ABSTRACT FROM AUTHOR]

We conducted pot experiments during the 2018–2020 growing seasons to study the effects of night warming at different growth stages of wheat on the photosynthetic performance; accumulation, transportation, and distribution of dry matter; and grain yield of winter wheat. Night warming at all the different growth stages resulted in an elevation of wheat yield by increasing the 1000-grain weight and the number of grains per ear. Night warming during the period from jointing to booting stage resulted in the greatest increase in wheat yield. It also increased the amount of overall dry matter and transferrable amount of dry matter in plants and increased the distribution of dry matter to grains to increase grain weight. Night warming treatments at three different growth stages enhanced pre-anthesis photosynthetic capacity by increasing flag leaf net photosynthetic rate, chlorophyll content, and photochemical efficiency of winter wheat at the early stage of grain filling, especially in the night warming treatment from jointing to booting stage. Night warming not only increased the stomatal density and stomatal index of wheat leaves but also increased stomatal conductance and transpiration rate in the early stage of grain filling, thus being conducive to the smooth progress of photosynthesis. In conclusion, night warming treatment at different growth stages increased the photosynthesis of flag leaves at the early stage of grain filling, and promoted the accumulation of dry matter in plants after anthesis, which was conducive to the grain yield of winter wheat. • Night warming promoted the accumulation of dry matter in plants after anthesis, which enhanced the grain yield of winter wheat. • Night warming not only increased the stomatal density and stomatal index of wheat leaves but also increased stomatal conductance and transpiration rate in the early stage of grain filling, thus being conducive to the smooth progress of photosynthesis. • Night warming from the jointing to booting stages resulted in the greatest increase in wheat yield. [ABSTRACT FROM AUTHOR]

Boron (B) toxicity is a major agricultural problem that causes a considerable decrease in crop yield and quality. The soil in arid and semi-arid areas is often subjected to excessive B content. Southwestern Perú (department of Tacna) is characterized by high B levels in its agricultural land and irrigation water. This work analyzes the response of two local maize (Zea mays) landraces (Pachía and Sama) from Tacna to B toxicity. Both landraces were, therefore, grown in hydroponic media under control and B toxicity conditions, and after 10 days, seedlings were harvested and B content, B-transporter gene expressions, and several morphological and physiological parameters were determined. The leaf and root soluble B content was lower in Sama than in Pachía when both landraces were subjected to high B concentrations, which could be explained by its higher expression levels of B-efflux transporters. The capacity of Sama to maintain reduced levels of soluble B in its leaves and roots led to decreased leaf damage and higher photosynthetic and growth parameters under B toxicity conditions. These results support the proposal that Sama would perform better than Pachía under excessive B conditions, thus making it a more suitable landrace to be used in soils with toxic levels of B. • The maize landrace Sama had a higher tolerance to high boron contents than Pachía. • Boron-toxicity tolerance of Sama is due to its ability to maintain low B levels. • Three boron-efflux transporters are involved in maintaining low boron contents. • Sama had higher photosynthesis and growth than Pachía under boron toxicity. • Sama showed better photoprotection than Pachía in media with high boron levels. [ABSTRACT FROM AUTHOR]

The involvement of auxin (IAA) in growth and development of plants is well known, but its role in the mitigation of metal stress, especially copper (Cu), is not fully understood; therefore, it is time to explore its involvement in minimizing the stress. A pot experiment was conducted to assess the protective function of IAA, applied to the foliage, on photosynthetic machinery, carbohydrate metabolism, and growth of Brassica juncea, grown with Cu (30 or 60 mg kg−1 of soil). Among the different concentrations (10−10, 10−8, or 10−6 M), 10−8 M of IAA alone enhanced the photosynthetic characteristics, sugar accumulation and vegetative growth with minimal cellular oxidative stress level. Moreover, the same concentration of auxin was most effective in decreasing the stress levels generated by Cu and maintained it nearly to that of the control in terms of photosynthetic attributes, gas exchange parameters, PSII activity, electron transport rate, and growth attributes. Auxin also maintained the membrane stability and ultrastructure of chloroplast, stomatal morphology with a reduction in malondialdehyde (MDA), electrolyte leakage (EL) and cell death in test plants even under Cu stress. IAA also improved the translocation of Cu from root to the aerial parts, thus enhanced the Cu-reclamation in metal contaminated soils. Our findings suggest that the application of 10−8 M of IAA maintains the overall growth of plants and may be used as an effective agent to improve growth, photosynthesis and phyto-remediation potential of B. juncea in Cu contaminated soil. • Excess Cu induces toxicity by inducing oxidative stress. • IAA spray improves the growth, photosynthesis and stress resilience. • IAA spray maintained chloroplast and stomata organization in Cu stressed plants. • IAA mitigated Cu generated toxicities by improving stress tolerance mechanisms. • IAA enhances Cu-remediation efficiency in mustard plants. [ABSTRACT FROM AUTHOR]

We present an approach to the noninvasive determination of the electron capacity of the intersystem pool of electron carriers in chloroplasts in situ. As apt experimental models, we used the leaves of Hibiscus rosa-sinensis and Tradescantia species. Electron paramagnetic resonance and optical response of P 700 (the primary electron donor in Photosystem I) were applied to measuring electron transport in chloroplasts. Electron capacities of the intersystem electron transport chain (ETC) were determined from redox transients of P 700 upon chromatic transitions (white light → far-red light). During the induction period, we observed the nonmonotonic changes in the number of electron equivalents in the intersystem ETC per P 700 (parameter Q). In Hibiscus rosa-sinensis , the light-induced rise of Q from ≈2.5 (in the dark) to Q ≈ 12 was followed by its decrease to Q ≈ 6. The data obtained are discussed in the context of pH-dependent regulation of electron transport in chloroplasts, which provides the well-balanced operation of the intersystem ETC. The decay of Q is explained by the attenuation of Photosystem II activity due to the lumen acidification and the acceleration of plastoquinol re-oxidation as a result of the Calvin-Benson cycle activation. Our computer model of electron and proton transport coupled to ATP synthesis in chloroplasts was used to analyze the up and down feedbacks responsible for pH-dependent regulation of electron transport in chloroplasts. The procedures introduced here may be important for subsequent works aimed at defining the plastoquinone participation in regulation of photosynthetic processes in chloroplasts in situ. • Method for determination of the intersystem electron capacity is developed. • We demonstrated non-monotonic dynamics of plastoquinone reduction/oxidation. • Computer model of electron and proton transport in chloroplasts is developed. [ABSTRACT FROM AUTHOR]

High temperature can induce a substantial adverse effect on plant photosynthesis. This study addressed the impact of moderately high temperature (35 °C) on photosynthetic efficiency and thylakoid membrane organization in Pisum sativum. The Chl a fluorescence curves showed a significant change, indicating a reduction in photosynthetic efficiency when pea plants were exposed to moderate high-temperature stress. The pulse-amplitude modulation measurements showed decreased non-photochemical quenching while the non-regulated energy dissipation increased in treated compared to control and recovery plants. Both parameters indicated that the photosystem (PS)II was prone to temperature stress. The PSI donor side limitation increased in treated and recovery plants compared to control, suggesting the donor side of PSI is hampered in moderate-high temperature. Further, the PSI acceptor side increased in recovery plants compared to control, suggesting that the cyclic electron transport is repressed after temperature treatment but revert back to normal in recovery conditions. Also, the content of photoprotective carotenoid pigments like lutein and xanthophylls increased in temperature-treated leaves. These results indicate the alteration of macro-organization of thylakoid membranes under moderately elevated temperature, whereas supercomplexes restored to the control levels under recovery conditions. Further, the light harvesting complex (LHC)II trimers, and monomers were significantly decreased in temperature-treated plants. Furthermore, the amount of PSII reaction center proteins D1, D2, PsbO, and Cyt b 6 was reduced under moderate temperature, whereas the content of LHC proteins of PSI was stable. These observations suggest that moderately high temperature can alter supercomplexes, which leads to change in the pigment-protein organization. • Chl a fluorescence and photosynthetic activity decrease in moderately high temperature treated plants. • The NPQ decreases in temperature-treated compared to recovery plants, but non-regulated energy dissipation increases. • Increase in Y(ND) indicates donor side of PSI is more hampered under moderately high-temperature. • The decreased supercomplexes were restored after 4 days of recovery condition. • The reaction center proteins of PSII were sensitive to temperature treatment, whereas the LHCs were stable. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deficiency is a primary limiting factor for crop production worldwide. Previously, we reported root system architectural modifications of hydroponically cultured foxtail millet [ Setaria italica (L.) Beauv.] to facilitate N translocation under N limitation. Here, we investigated foxtail millet for its shoot adaptation to low N in terms of internal N regulation under hydroponic culture. The results of this study revealed that the shoot N and nitrate (NO 3 −) concentrations significantly declined as compared to control (CK); however, the shoot over-accumulated ammonium (NH 4 +) under low N (LN). N shortage resulted in down-regulation of expressions of SiPetA, SiccsA, SipsbA, SirpoB, SipsaA, SiatpA, Sirps16 , and SiPEPC which, undermined chloroplast functioning and CO 2 assimilation for the provision of carbon skeleton. Carbon deficiency and lower activities of GS decelerated ammonia assimilation and led to over-accumulation of NH 4 + in the LN-shoot, as indicated by lower concentrations of total amino acids. Thus, enhanced GOGAT activity was to assimilate NH 4 + while, those of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) were to scavenge reactive oxygen species (ROS) of NH 4 + toxicity framework. The weakened chloroplast factory eventually minimized photosynthesis and reduced dry mass of the LN shoot. Such regulation of N by the shoot, perhaps, resurrected physiological functions which maintained internal mineral status under nitrogen limitation in foxtail millet. • The shoot over-accumulated ammonium (NH 4 +) under low N. • N shortage undermined chloroplast functioning and provision of carbon skeleton. • Carbon skeleton shortage hampered GOGAT/GS functioning. [ABSTRACT FROM AUTHOR]

In this study, we have explored potential of a nitric oxide (NO) donor (SNP, sodium nitroprusside) and hydrogen peroxide (H 2 O 2) in curtailing stress of hexavalent chromium [Cr(VI)] in wheat seedlings. Cr(VI) stress caused a significant decline in growth (30%) and photosynthesis (13%) as a result of enhanced uptake of Cr(VI) and root tips cell death. Further, Cr(VI) stress also accelerated indices of oxidative stress but differentially regulated antioxidant system. But application of either NO or H 2 O 2 separately significantly mitigated Cr(VI) stress by reducing cell death and Cr(VI) uptake in roots, and oxidative stress markers. The application of c-PTIO [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a scavenger of NO] and N -acetyl- L -cysteine (a scavenger of ROS) reserved alleviatory effect of NO and H 2 O 2 , respectively and thus further increased Cr(VI) toxicity. Application of diphenylene iodonium (DPI, an inhibitor of NADPH oxidases) also further increased Cr(VI) toxicity. But SNP and H 2 O 2 significantly rescued negative effects of DPI and c-PTIO, respectively under Cr(VI) stress. Overall results suggested that NO and H 2 O 2 both independently act in mitigating Cr(VI) stress in wheat seedlings by minimizing cell death, restricting Cr(VI) uptake in roots, and increasing antioxidant system, sulfur assimilation and proline metabolism. [Display omitted] • Cr(VI) stress resulted into significant decline in growth. • But NO or H 2 O 2 separately significantly mitigated Cr(VI) stress. • SNP and H 2 O 2 rescued negative effects of DPI and c-PTIO, respectively. • NO and H 2 O 2 up-regulate sulfur assimilation and proline level. • NO and H 2 O 2 both are independently able in mitigating Cr(VI) stress. [ABSTRACT FROM AUTHOR]

Vanilla planifolia is an obligate sciophyte (shade plant) with crassulacean acid metabolism (CAM) photosynthesis. Plants were grown for 12 months under black, blue, green, or red photoselective shade netting (PSN) to alter the spectral light distribution impacting the plants. Light wavelengths were measured in each treatment and plants were assessed for photosynthetic characteristics, leaf chlorophyll index (LCI), maximum quantum yield of photosystem II, leaf reflectance indices, leaf area, growth, antioxidant enzymes, lipid peroxidation, reactive oxygen species (ROS), and osmolyte content. Plants grown under red PSN had a higher quantity of red and far-red light and had greater nocturnal net CO 2 assimilation (Noc A), leaf area and leaf dry weight than plants in the other treatments. Plants grown under blue PSN had a higher quantity of blue light, resulting in a higher LCI and maximum quantum yield than plants in the other treatments. Plants grown under the red and blue PSN had increased leaf spectral reflectance indices compared to plants in the other treatments, which resulted in the highest levels of antioxidant scavenging enzymes, ascorbic acid (AsA), proline, and glycine betaine, and the lowest levels of H 2 O 2. These findings demonstrate that increasing light in the red and far-red or blue portions of the spectrum by using PSN alters the photosynthetic and/or antioxidant responses of V. planifolia and increasing red and far-red light by using red PSN can also accelerate plant growth, possibly due to higher photosynthesis. • Red photoselective shade netting (PSN) increased nocturnal net CO 2 assimilation and growth of Vanilla planifolia • Blue PSN increased chlorophyll content and maximum quantum yield of photosystem II • Red or blue PSN increased leaf antioxidant activity [ABSTRACT FROM AUTHOR]

Potassium (K) is an important cation that regulates plant metabolism. Therefore the effect of different concentrations of potassium (0, 75, 150 kg ha−1 K 2 SO 4) on photosynthesis efficiency of three winter wheat cultivars (Baran, Homa, Hashtrud) was investigated during the growing seasons of 2017–18 and 2018–19 under cold dryland conditions in Maragheh, Iran. Accumulation of potassium ion (K+) was observed to be increased with an increase in the concentration of K 2 SO 4. With an increase in K+ the Hashtrud cultivar was observed to have more relative water content (RWC), normalized differential vegetation index (NDVI), and stomatal conductance (gs) than other cultivars. This resulted in a higher grain yield for the Hashtrud cultivar. RWC (R2 = 0.97), NDVI (R2 = 0.96), and gs (R2 = 0.92) had a positive relationship with KUE (grain yield/unit of K fertilizer used), especially in dryer years. K deficiency induced hydrogen peroxide (H 2 O 2) and malondialdehyde (MDA) concentration in plants. The application of K increased superoxide dismutases and reduced abscisic acid, to maintain the plants' stomatal conductance. Chlorophyll a fluorescence (ChlF) and the calculation of double normalized relative variable fluorescence reveal detailed information's about the response of wheat plants to K application under dryland conditions. The application of a high concentration of K (150 kg ha−1 K 2 SO 4) on Hashtrud plants had a beneficial effect on the ChlF efficiency at different OJIP phases (KJ and JI). We found the efficiency of ChlF at the ΔW K-I phase with the values of F V /F O and PI ABS improved with the application of 150 kg ha−1 K 2 SO 4 and can be correlated with total yield improvement. These observations indicated that the application of a high concentration of K in stressed conditions for dryland areas could improve photosynthetic efficiency and wheat plant performance. • Application of potassium improve photosynthetic efficiency and wheat plant performance. • Potassium deficiency induce free radicle formation in plants. • Application of Potassium declined the concentration of Abscisic acid in wheat cultivars. [ABSTRACT FROM AUTHOR]

Leaf senescence occurs as the last developmental phase of leaf. The initiation and progression of leaf senescence is highly regulated by a plethora of internal developmental signals and environmental stimuli. Being an important class of phytohormones, jasmonates (JAs) are shown to induce premature leaf senescence in tomato (Solanum lycopersicum), nevertheless, the underlying mechanisms remain enigmatic. Here, we report that tomato MYC2, a key factor in the JA signal transduction, functions in JA-induced tomato leaf senescence by promoting chlorophyll degradation and inhibiting photosynthetic carbon fixation. We found that exogenous application of MeJA reduced chlorophyll content, decreased carbon assimilation rates and disrupted membrane integrity. We further demonstrated using SlMYC2-RNAi tomato plants that SlMYC2 enhanced the expression of SlPAO , which encodes a chlorophyll degradation enzyme, but suppressed the expression of SlRCA and SlSBPASE , both of which are required for photosynthesis and growth in plants. Dual-luciferase assay confirmed that SlMYC2 activated the transcription of SlPAO , but inhibited the transcription of SlRCA and SlSBPASE. Furthermore, repression of SlRCA led to typical features associated with leaf senescence in tomato. Taken together, these results favor that tomato MYC2 acts positively in the regulation of JA-dependent tomato leaf senescence. The results extend our mechanistic understanding of JA-induced senescence in an important horticultural crop. •Jasmonate reduces chlorophyll content and decreases carbon assimilation rates. • SlMYC2 enhances the expression of SlPAO , which encodes a chlorophyll degradation enzyme. • SlMYC2 suppresses the expression of SlRCA and SlSBPASE , both required for photosynthesis. • Repression of SlRCA leads to tomato leaf senescence. [ABSTRACT FROM AUTHOR]

Photosynthesis is crucial for the survival of all living biota, playing a key role in plant productivity by generating the carbon skeleton that is the primary component of all biomolecules. Salinity stress is a major threat to agricultural productivity and sustainability as it can cause irreversible damage to photosynthetic apparatus at any developmental stage. However, the capacity of plants to become photosynthetically active under adverse saline conditions remains largely untapped. This study addresses this discrepancy by exploring the current knowledge on the impact of salinity on chloroplast operation, metabolism, chloroplast ultrastructure, and leaf anatomy, and highlights the dire consequences for photosynthetic machinery and stomatal conductance. We also discuss enhancing photosynthetic capacity by modifying and redistributing electron transport between photosystems and improving photosystem stability using genetic approaches, beneficial microbial inoculations, and root architecture changes to improve salt stress tolerance under field conditions. Understanding chloroplast operations and molecular engineering of photosynthetic genes under salinity stress will pave the way for developing salt-tolerant germplasm to ensure future sustainability by rehabilitating saline areas. • Plant capacity to become photosynthetically active under salinity remains largely untapped. • Modifying electron transport and photosystem stability improve photosynthesis under salinity. • Using beneficial microbial and root architecture changes enhance salt tolerance. • Engineering of photosynthetic genes may help developing salt-tolerant plant genotypes. [ABSTRACT FROM AUTHOR]

Pistia stratiotes is a cadmium (Cd) hyperaccumulating plant with strong bioaccumulation and translocation capacity for Cd. A hydroponic experiment was used to evaluate the combined effect of Zinc (Zn) and Cd at different concentrations on leaf growth and metabolism of P. stratiotes. This study revealed the physiological defense and metabolic strategy of responses to Zn–Cd co-pollution. With the Zn 50 Cd 1 , Zn 50 Cd 10 , Zn 100 Cd 1, and Zn 100 Cd 10 treatments for 9 d, the relative crown diameter, relative leave number, and ramet number of the plant had no significant difference with the control. Under the compound treatments containing Zn 50 Cd 50 and Zn 100 Cd 50 , the activity of the glyoxalase system and amino acid metabolism in the leaves were inhibited. The leaf photosynthetic apparatus increased heat dissipation to reduce the damage to the photosystem II (PS II) reaction center caused by excess excitation energy under Zn–Cd stress. This safeguarded the balance between the absorption and utilization of light energy. Compared to the control, the Zn and Cd co-pollution for 9 d had no effect on the reduced glutathione (GSH) and oxidized glutathione (GSSG) contents. There was no effect on the dehydroascorbate reductase (DHAR) and glutathione reductase (GR) activities, but there was increased ascorbate peroxidase (APX) activity and oxidized ascorbic acid (DHA) content. These increased the antioxidant capacity of the ascorbate-glutathione (AsA-GSH) cycle. The treated plants also had increased levels of carnosol and substances related to lipid metabolism including 9, 10-Dihydroxystearate, Prostaglandin G2, Sphingosine, and 13-L-Hydroperoxylinoleic acid, maintaining the cell stability and resistance to the Zn–Cd stress. [Display omitted] • The redox reaction equilibrium of glutathione maintained the antioxidant stability. • Increased carnosol and lipid metabolism were conducive to zinc-cadmium tolerance. • Pistia stratiotes can be used for phytoremediation of zinc-cadmium polluted water. [ABSTRACT FROM AUTHOR]

Industrialization-driven surface ozone (O 3) pollution significantly impairs plant growth. This study evaluates the effectiveness of exogenous protectants [3 mg L⁻1 abscisic acid (ABA), 400 mg L⁻1 ethylenediurea (EDU), and 80 mg L⁻1 spermidine (Spd)] on Trifolium repens subjected to O 3 stress in open-top chambers, focusing on plant growth and dynamics of culturable endophytic fungal communities. Results indicate that O 3 exposure adversely affects photosynthesis, reducing root biomass and altering root structure, which further impacts the ability of plant to absorb essential nutrients such as potassium (K), magnesium (Mg), and zinc (Zn). Conversely, the application of ABA, EDU, and Spd significantly enhanced total biomass and chlorophyll content in T. repens. Specifically, ABA and Spd significantly improved root length, root surface area, and root volume, while EDU effectively reduced leaves' malondialdehyde levels, indicating decreased oxidative stress. Moreover, ABA and Spd treatments significantly increased leaf endophytic fungal diversity, while root fungal abundance declined. The relative abundance of Alternaria in leaves was substantially reduced by these treatments, which correlated with enhanced chlorophyll content and photosynthesis. Concurrently, EDU and Spd treatments increased the abundance of Plectosphaerella , enhance the absorption of K, Ca, and Mg. In roots, ABA treatment increased the abundance of Paecilomyces , while Spd treatment enhanced the presence of Stemphylium , linked to improved nitrogen (N), phosphorus (P), and K uptake. These findings suggest that specific symbiotic fungi mitigate O 3 -induced stress by enhancing nutrient absorption, promoting growth. This study highlights the potential of exogenous protectants to enhance plant resilience against O 3 pollution through modulating interactions with endophytic fungal communities. [Display omitted] • Elevated O 3 impairs T. repens growth by reducting photosynthesis. • Exogenous protectants enhance biomass and especially promote root growth of T. repens under O 3 stress. • Exogenous protectants alter fungi community and affect nutrient uptake of T. repens. [ABSTRACT FROM AUTHOR]

Strigolactone (SL), a plant hormone derived from carotenoids, has been recognized for its pivotal role in regulating plant growth. Nevertheless, the influence of SL on tall fescue (Festuca arundinacea) under low-light conditions remains unclear. This study aimed to investigate the impact of SL on various aspects of tall fescue, including its morphological characteristics, photosynthesis, levels of antioxidant and concentrations of SL, under low light intensity (LI). The findings showed that GR24, an artificial analog of SL, positively influenced several parameters of tall fescue under LI. In particular, it enhanced the morphological features such as plant height, leaf width, and biomass, while reducing the number of tillers. Furthermore, it improved the efficiency of photosynthetic by enhancing chlorophyll fluorescence and the gas exchange parameters, mitigating cell damage and improving the contents of antioxidants by increasing the levels of antioxidant enzymes and non-enzymatic antioxidant compounds. Moreover, treatment with SL led to elevated concentrations of this hormone and the levels of gene expression in related pathways. Owing to the immaturity of the genetic transformation system in tall fescue, partial validation through transgenic and mutant materials was obtained using Arabidopsis (Arabidopsis thaliana). These findings demonstrate that SL alleviates the physiological indicators of tall fescue under LI stress and enhances its tolerance to shade. Additionally, it suggests that SL may regulate the shade tolerance of tall fescue through the involvement of FaD14. • Strigolactone (SL) enhanced morphological features under low-light intensity (LI) stress. • SL improved photosynthetic efficiency under LI stress. • SL mitigated cell damage and improved antioxidant capacity under LI stress. • The FaD14 involved the shade tolerance of tall fescue. [ABSTRACT FROM AUTHOR]

Castanea sativa Miller, a high-valuable crop for Mediterranean countries, is facing frequent and prolonged periods of heat and drought, severely affecting chestnut production. Aiming to tackle this problem, this study unraveled the influence of mycorrhizal association with the fungi Paxillus involutus (Batsch) on young chestnut plants' responses to combined heat (42 °C; 4 h/day) and drought (no irrigation until soil moisture reached 25%) over 21 days of stress exposure. Heat stress had no harmful effects on growth, photosynthesis, nor induced oxidative stress in either mycorrhizal (MR) or non-mycorrhizal (NMR) chestnut plants. However, drought (alone or combined) reduced the growth of NMR plants, affecting water content, leaf production, and foliar area, while also hampering net CO 2 assimilation and carbon relations. The mycorrhizal association, however, mitigated the detrimental effects of both stresses, resulting in less susceptibility and fewer growth limitations in MR chestnut plants, which were capable of ensuring a proper carbon flow. Evaluation of the oxidative metabolism revealed increased lipid peroxidation and hydrogen peroxide levels in NMR plants under water scarcity, supporting their higher susceptibility to stress. Conversely, MR plants activated defense mechanisms by accumulating antioxidant metabolites (ascorbate, proline and glutathione), preventing oxidative damage, especially under the combined stress. Overall, drought was the most detrimental condition for chestnut growth, with heat exacerbating stress susceptibility. Moreover, mycorrhizal association with P. involutus substantially alleviated these effects by improving growth, water relations, photosynthesis, and activating defense mechanisms. Thus, this research highlights mycorrhization's potential to enhance C. sativa resilience against climate change, especially at early developmental stages. • Drought impaired chestnut plants' physiology and redox status. • Heat stress exacerbated drought effects on non-mycorrhizal chestnut plants. • Mycorrhization mitigated the effects of heat and drought co-exposure. • ECM association boosted defence mechanisms, ensuring growth under stress. [ABSTRACT FROM AUTHOR]

Excess of selenium (Se) in aquatic ecosystems has necessitated thorough investigations into the effects/consequences of this metalloid on the autochthonous organisms exposed to it. The molecular details of Se-mediated adaptive response remain unknown in cyanobacteria. This study aims to uncover the molecular mechanisms driving the divergent physiological responses of cyanobacteria on exposure to selenate [Se(VI)] or selenite [Se(IV)], the two major water-soluble oxyanions of Se. The cyanobacterium, Anabaena PCC 7120 , withstood 0.4 mM of Se(VI), whereas even 0.1 mM of Se(IV) was detrimental, affecting photosynthesis and enhancing endogenous ROS. Surprisingly, Anabaena pre-treated with Se(VI), but not Se(IV), showed increased tolerance to oxidative stress mediated by H 2 O 2 /methyl viologen. RNA-Seq analysis showed Se(VI) to elevate transcription of genes encoding anti-oxidant proteins and Fe–S cluster biogenesis, whereas the photosynthesis-associated genes, which were mainly downregulated by Se(IV), remained unaffected. Specifically, the content of typical 2-Cys-Prx (Alr4641), a redox-maintaining protein in Anabaena , was elevated with Se(VI). In comparison to the wild-type, the Anabaena strain over-expressing the Alr4641 protein (An4641+) showed enhanced tolerance to Se(VI) stress, whereas the corresponding knockdown-strain (KD4641) was sensitive to this stressor. Incidentally, among these strains, only An4641+ was better protected from the ROS-mediated damage caused by high dose of Se(VI). These results suggest that altering the content of the antioxidant protein 2-Cys-Prx, could be a potential strategy for modulating resistance to selenate. Thus, involvement of oxidative stress machinery appears to be the major determinant, responsible for the contrasting physiological differences observed in response to selenate/selenite in cyanobacteria. [Display omitted] • Between the two soluble species of Se, Anabaena was more tolerant to Se(VI) than Se(IV). • Se(IV), which caused more oxidative stress than Se(VI), severely affected photosynthesis. • Pre-treatment with Se(VI), but not Se(IV), enhanced oxidative stress resistance. • Se(VI) elevated transcription of antioxidant protein-encoding genes while Se(IV) did not. • The 2-Cys-Peroxiredoxin enhanced resistance to Se(VI) by alleviating oxidative stress. [ABSTRACT FROM AUTHOR]