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Transgenic Arabidopsis thaliana (ecotype Columbia) was successfully transformed with the gene fructose-1,6-bisphosphatase (FBPase) and named as AtFBPase plants. Transgenic plants exhibited stable transformation, integration and significantly higher expressions for the transformed gene. Morphological evaluation of transgenic plants showed increased plant height (35 cm), number of leaves 25), chlorophyll contents (28%), water use efficiency (increased from 1.5 to 2.6 µmol CO2 µmol-1 H2O) and stomatal conductance (20%), which all resulted in an enhanced photosynthetic rate 2.7 µmol m-2 s-1) compared to wild type plants. This study suggests the vital role of FBPase gene in the modification of regulatory pathways to enhance the photosynthetic rate, which can also be utilised for economic crops in future. [ABSTRACT FROM AUTHOR]

Continuous increasing leaf photosynthesis may enhance plant yield. As an evolutionary property, plants use less photosynthetic capacity than is theoretically possible. Plant nanobionics is a bioengineering field that improves plant functions using nanoparticles. We applied orange carbon dots (o-CDs) onto the foliage of green beans (Phaseolus vulgaris) grown in hydroponics to improve their photosynthetic performance and CO2 assimilation. Photosynthesis parameters, photosynthetic pigments content, total phenolic content (TPC) and antioxidative activity (TAA) were measured. Results show that photosynthetic pigments remained unchanged, while photosynthesis was improved. Both o-CDs concentrations decreased TPC and TAA. The light response curve showed higher CO2 assimilation at both o-CDs concentrations, particularly at lower light intensity. Correlation analysis confirmed increased CO2 binding and assimilation at 1 mg L−1. This study demonstrated the potential of using o-CDs as a safe biostimulator through photosynthesis increase and CO2 assimilation without toxic effects on plants. This may stimulate yield increase that paves the way for their agricultural application. [ABSTRACT FROM AUTHOR]

Orchids (Phalaenopsis spp.) growing in tropical and subtropical regions are epiphytes. As such, they grow on trees with the root system utilised to anchor themselves to tree branches. These roots are highly specialised, display a large diameter and are often green, suggesting the ability to carry out photosynthesis. However, the role of photosynthesis in orchid roots is controversial. Orchids that are leafless can photosynthesise in their roots, thus indicating that some orchid roots carry out photosynthesis in a similar manner to leaves. However, the primary site of photosynthesis in orchids are in their leaves, and the roots of epiphytic orchids may mostly conduct internal refixation of respiratory CO2. Besides contributing to the overall carbon metabolism of orchid plants, oxygen produced through root photosynthesis may also be important by alleviating potential root hypoxia. The bulky tissue of most epiphytic orchid roots suggests that oxygen diffusion in these roots can be limited. Here, we demonstrate that the bulky roots of a widely commercially cultivated orchid belonging to the genus Phalaenopsis are hypoxic in the dark. These roots are photosynthetically active and produce oxygen when exposed to light, thus mitigating root hypoxia. Orchid (Phalaenopsis spp.) is a most popular flowering potted plant. However, it has been poorly studied at the physiological and molecular level. The bulky aerial roots of Phalaenopsis have a large diameter and are possibly photosynthetically active. Here, we present evidence demonstrating that root photosynthesis prevents hypoxia in the root tissue. Our results support the existence of hypoxic niches in plant roots and highlight the existence of mechanisms to modulate the intensity of hypoxia. This article belongs to the Collection Flooding Stress and Hypoxic Responses in Plants. [ABSTRACT FROM AUTHOR]

Plant growth and development is adversely affected by environmental constraints, particularly salinity and drought. Climate change has escalated the effect of salinity and drought on crops in varying ways, affecting agriculture and most importantly crop productivity. These stressors influence plants across a wide range of levels, including their morphology and physiological, biochemical, and molecular processes. Plant responses to salinity and drought stress have been the subject of intense research being explored globally. Considering the importance of the impact that these stresses can have on agriculture in the short term, novel strategies are being sought and adopted in breeding programs. Better understanding of the molecular, biochemical, and physiological responses of agriculturally important plants will ultimately help promote global food security. Moreover, considering the present challenges for agriculture, it is critical to consider how we can effectively transfer the knowledge generated with these approaches in the laboratory to the field, so as to mitigate these adversities. The present collection discusses how drought and salinity exert effects on plants. Environmental constraints like salinity and drought hinder plant growth by affecting plant morphology, physiology, biochemistry, and molecular processes, final crop productivity and threat to global food security. Researches on plant responses to salinity and drought stress is ongoing worldwide. Novel breeding strategies are being adopted due to their short-term impact on agriculture. Given agriculture's current challenges, we must consider how to effectively transfer laboratory knowledge to the field to mitigate these challenges. This collection discusses plant responses to drought and salinity. This article belongs to the Collection Understanding the Mechanistic Basis of Plant Adaptation to Salinity and Drought. [ABSTRACT FROM AUTHOR]

Water stress (drought and waterlogging) leads to an imbalance in plant water distribution, disrupts cell homeostasis, and severely inhibits plant growth. Melatonin is a growth hormone that plants synthesise and has been shown to resist adversity in many plants. This review discusses the biosynthesis and metabolism of melatonin, as well as the changes in plant morphology and physiological mechanisms caused by the molecular defence process. Melatonin induces the expression of related genes in the process of plant photosynthesis under stress and protects the structural integrity of chloroplasts. Exogenous melatonin can maintain the dynamic balance of root ion exchange under waterlogging stress. Melatonin can repair mitochondria and alleviate damage caused by reactive oxygen species and reactive nitrogen species; and has a wide range of uses in the regulation of stress-specific genes and the activation of antioxidant enzyme genes. Melatonin improves the stability of membrane lipids in plant cells and maintains osmotic balance by regulating water channels. There is crosstalk between melatonin and other hormones, which jointly improve the ability of the root system to absorb water and breathe and promote plant growth. Briefly, as a multifunctional molecule, melatonin improves the tolerance of plants under water stress and promotes plant growth and development. Melatonin, as an exogenous hormone, has been widely used in improving plant stress resistance. This paper systematically describes how melatonin improves the ability of plants to resist water stress (drought and waterlogging) in the processes of photosynthesis, antioxidation and osmosis at the physiological and genetic levels. Melatonin can also improve plant stress resistance with other hormone crosstalk, which has high application value. [ABSTRACT FROM AUTHOR]

In this study, we investigated the importance of one of the intramembrane proteases, EGY2, for the proper functioning of PSII under short-term high light stress conditions. EGY2 is a chloroplast intramembrane protease of the S2P family, whose absence in Arabidopsis thaliana affects PSII protein composition. The egy2 mutants exhibited a slower degradation of PsbA and decreased content of PsbC and PsbD. During exposure to high light stress, these stoichiometric changes affect the functional state of PSII, leading to its higher sensitivity to photoinhibition of the PSII reaction centre and increased heat dissipation. Furthermore, we explored the relationship between EGY2 and the pTAC16 transcription factor, which is a potential EGY2 substrate. Under light stress, WT plants showed decreased levels of pTAC16, while it remained unchanged in the egy2 mutants. This finding suggests that EGY2 may release pTAC16 from thylakoid membranes through proteolytic cleavage. We also confirmed the physical interaction between EGY2 and pTAC16 using the yeast two-hybrid system, providing evidence of EGY2's involvement in the regulation of PsbA and PsbC/PsbD operons by releasing pTAC16 from the thylakoid membrane. [ABSTRACT FROM AUTHOR]

Viscum schimperi is an evergreen hemiparasitic plant that can grow on stems and branches of several tree species. It penetrates the host tissues and forms a vascular bridge (haustorium) to withdraw the nutritive resources. Its relationships with hosts remain unknown. This study aimed to investigate the physiological and biochemical attributes of the host-hemiparasite association Acacia gerrardii-Viscum schimperi. The hemiparasite exhibited 2.4- and 3.0-fold lower photosynthetic activity and water use efficiency, and 1.2- and 4.1-fold higher transpiration rate and stomatal conductance. Equally, it displayed 4.9- and 2.6-fold greater water potential and osmotic potential, and in least 3.0 times more accumulated 39K, 85Rb and 51V, compared to the host. Nevertheless, it had no detrimental effect on photosynthetic activity, water status and multi-element accumulations in the host. Based on metabolome profiling, V. schimperi could use xanthurenic acid and propylparaben to acquire potassium from the host, and N-1-naphthylacetamide and N-Boc-hydroxylamine to weaken or kill the distal part of the infected branch and to receive the total xylem contents. In contrast, A. gerrardii could used N-acetylserotonin, arecoline, acetophenone and 6-methoxymellein to defend against V. schimperi infection. [ABSTRACT FROM AUTHOR]

Solanaceous crops act as a source of food, nutrition and medicine for humans. Soil salinity is a damaging environmental stress, causing significant reductions in cultivated land area, crop productivity and quality, especially under climate change. Solanaceous crops are extremely vulnerable to salinity stress due to high water requirements during the reproductive stage and the succulent nature of fruits and tubers. Salinity stress impedes morphological and anatomical development, which ultimately affect the production and productivity of the economic part of these crops. The morpho-physiological parameters such as root-to-shoot ratio, leaf area, biomass production, photosynthesis, hormonal balance, leaf water content are disturbed under salinity stress in Solanaceous crops. Moreover, the synthesis and signalling of reactive oxygen species, reactive nitrogen species, accumulation of compatible solutes, and osmoprotectant are significant under salinity stress which might be responsible for providing tolerance in these crops. The regulation at the molecular level is mediated by different genes, transcription factors, and proteins, which are vital in the tolerance mechanism. The present review aims to redraw the attention of the researchers to explore the mechanistic understanding and potential mitigation strategies against salinity stress in Solanaceous crops, which is an often-neglected commodity. [ABSTRACT FROM AUTHOR]

In this study, agronomic and functional characteristics of potato (Solanum tuberosum) plants constitutively overexpressing the protein phosphatase 2A (PP2A) catalytic subunit StPP2Ac2b (StPP2Ac2b-OE) were evaluated. StPP2Ac2b-OE plants display reduced vegetative growth, tuber yield and tuber weight under well-watered and drought conditions. Leaves of StPP2Ac2b-OE plants show an increased rate of water loss, associated with an impaired ability to close stomata in response to abscisic acid. StPP2Ac2b-OE lines exhibit larger stomatal size and reduced stomatal density. These altered stomatal characteristics might be responsible for the impaired stomatal closure and the elevated transpiration rates, ultimately leading to increased sensitivity to water-deficit stress and greater yield loss under drought conditions. Overexpression of StPP2Ac2b accelerates senescence in response to water-deficit stress, which could also contribute to the increased sensitivity to drought. Actively photosynthesising leaves of StPP2Ac2b-OE plants exhibit elevated levels of carbohydrates and a down-regulation of the sucrose transporter StSWEET11 , suggesting a reduced sucrose export from leaves to developing tubers. This effect, combined with the hindered vegetative development, may contribute to the reduced tuber weight and yield in StPP2Ac2b-OE plants. These findings offer novel insights into the physiological functions of PP2A in potato plants and provide valuable information for enhancing potato productivity by modulating the expression of StPP2Ac2b. This study provides novel insights into the physiological functions of protein phosphatase 2A in potato (Solanum tuberosum) plants. The results obtained reveal that the catalytic subunit StPP2Ac2b is involved in stomatal development, senescence induced by water-deficit stress and sucrose export from leaves. Manipulating the expression of StPP2Ac2b has significant effects on these physiological processes, ultimately impacting on important agronomic traits. This work presents valuable information for improving potato productivity by modulating the expression of StPP2Ac2b. [ABSTRACT FROM AUTHOR]

Anthracnose caused by Colletotrichum gloeosporioides critically threatens the growth and commercial cultivation of Sarcandra glabra. However, the defence responses and underlying mechanisms remain unclear. Herein, we aimed to investigate the molecular reprogramming in S. glabra leaves infected with C. gloeosporioides. Leaf tissues at 0, 24 and 48 h post-inoculation (hpi) were analysed by combining RNA sequencing and Tandem Mass Tag-based liquid chromatography with tandem mass spectrometry. In total, 18 441 and 25 691 differentially expressed genes were identified at 24 and 48 hpi compared to 0 hpi (uninoculated control), respectively. In addition, 1240 and 1570 differentially abundant proteins were discovered at 24 and 48 hpi compared to 0 hpi, respectively. Correlation analysis revealed that transcription and translation levels were highly consistent regarding repeatability and expression. Analyses using databases KEGG and iPATH revealed tricitric acid cycle, glycolysis/gluconeogenesis and phenylpropanoid biosynthesis were induced, whereas photosynthesis and tryptophan were suppressed. Enzymatic activity assay results were consistent with the upregulation of defence-related enzymes including superoxide dismutases, catalases, peroxidases and chitinases. The transcriptome expression results were additionally validated by quantitative real-time polymerase chain reaction analyses. This study provides insights into the molecular reprogramming in S. glabra leaves during infection, which lay a foundation for investigating the mechanisms of host- Colletotrichum interactions and breeding disease-resistant plants. Anthracnose caused by Colletotrichum gloeosporioides critically threatens the growth and commercial cultivation of the medicinal plant Sarcandra glabra. We explored the molecular changes during the early stages of this infection through systems biology. This study provides insights into the molecular reprogramming in S. glabra leaves during infection, which lay a foundation for investigating the mechanisms of host -Colletotrichum interactions and breeding disease-resistant plants. [ABSTRACT FROM AUTHOR]

Soil salinisation is one of the main abiotic stresses decreasing crop productivity. Here, we show that the plant treatment with iron oxide (Fe3O4) nanoparticles (NPs) may be a promising solution for reducing the negative impact of soil salinity on plant performance. For this purpose, effects of the NPs on growth, photosynthesis, pro-/antioxidant, redox balance and the content of mineral elements in 19-day-old wheat (Triticum aestivum) plants under soil salinity were studied. Seed treatment with NPs (200 and 500 mg L−1) enhanced growth and photosynthetic rate in leaves. Moderate salinity stress (150 mM NaCl) led to a decrease in plant biomass as well as the rate of photosynthesis and PSII activity; leaf photosynthetic characteristics were also suppressed by lower (75 mM NaCl) salinity treatment. However, seed pre-treatment with the NPs partially eliminated the negative effect of the salt on growth, PSII activity and photosynthesis. Also, we observed a decrease in the content of malondialdehyde (MDA) and an increase in ascorbate and total peroxidase activity in the plant leaves upon combined treatment with NaCl and the NPs compared with treatment with NaCl alone. The combined treatment with the NPs and salinity also led to a noticeable increase in the content of Fe and Mn in the shoot. It was concluded that Fe3O4 NPs can enhance plant growth by improving photosynthetic characteristics, antioxidant balance and the availability of iron and manganese ions, under conditions of soil salinisation. Soil salinity significantly affects productivity of agricultural systems. This work shows that plant treatment with iron oxide nanoparticles (Fe3O4 NPs) may be a promising solution for reducing the negative impact of soil salinity on plant performance. It is concluded that Fe3O4 NPs can enhance plant growth by improving photosynthetic characteristics, antioxidant balance and the availability of iron and manganese ions, under conditions of soil salinisation. [ABSTRACT FROM AUTHOR]

Cool temperatures can limit productivity of temperate grazing systems as poor pasture growth rates in winter create feed shortages for livestock. Ornithopus spp. (serradella) are broadly adapted annual pasture legumes that produce high-quality forage in soil types considered marginal for other temperate legume species. However, serradella establishment is perceived to be difficult in cool-season environments. We used survival analysis to compare germination rate and seedling emergence for two serradella species (yellow serradella and French serradella) against three reference species (Medicago sativa, M. polymorpha and Trifolium subterraneum) in four temperature treatments (10/5, 15/10, 20/15 and 25/20°C; max/min). We also compared shoot relative growth rate and photosynthetic rate at 15/10°C (cool) and 23/18°C (warm). Cool temperatures (10/5, 15/10°C) did not slow germination rates for serradella relative to the reference species, but warm temperatures (20/15, 25/20°C) delayed emergence and reduced post-emergent shoot growth rates. Once established, Ornithopus spp. had similar mean photosynthetic rates and stomatal conductance at cool temperatures to the reference species.We conclude that, contrary to common perception, cool temperatures did not adversely influence germination, emergence, or early growth of Ornithopus spp. relative to the reference species. [ABSTRACT FROM AUTHOR]

Lower plants such as bryophytes often encounter submergence stress, even in low precipitation conditions. Our study aimed to understand the mechanism of submergence tolerance to withstand this frequent stress in moss (Semibarbula orientalis) during the day and at night. These findings emphasise that light plays a crucial role in photoreactivation of PSII in S. orientalis, which indicates that light not only fuels photosynthesis but also aids in repairing the photosynthetic machinery in plants. Submergence negatively affects photosynthesis parameters such as specific and phenomenological fluxes, density of functional PSII reaction centres (RC/CS), photochemical and non-photochemical quenching (Kp and Kn), quantum yields (φP0, φE0, φD0), primary and secondary photochemistry, performance indices (PIcs and PIabs), etc. Excessive antenna size caused photoinhibition at the PSII acceptor side, reducing the plastoquinone pool through the formation of PSII triplets and reactive oxygen species (ROS). This ROS-induced protein and PSII damage triggered the initiation of the repair cycle in presence of sunlight, eventually leading to the resumption of PSII activity. However, ROS production was regulated by antioxidants like superoxide dismutase (SOD) and catalase (CAT) activity. The rapid recovery of RS/CS observed specifically under sunlight conditions emphasises the vital role of light in enabling the assembly of essential units, such as the D1 protein of PSII, during stress in S. orientalis. Overall, light is instrumental in restoring the photosynthetic potential in S. orientalis growing under submergence stress. Additionally, it was observed that plants subjected to submergence stress during daylight hours rapidly recover their photosynthetic performance. However, submergence stress during the night requires a comparatively longer period for the restoration of photosynthesis in the moss S. orientalis. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the photosynthetic performance of Zanthoxylum armatum seedlings to test the tolerance to reoxygenation after waterlogging. The experiment included a control group without waterlogging (NW) and three reoxygenation groups with reoxygenation after 1 day (WR1), 2 days (WR2) and 3 days (WR3). Seedlings were pretreated with concentrations of 0, 200 and 400 μmol L−1 of ethylene. The results showed that reoxygenation after waterlogging for 1–3 days decreased photosynthetic pigments content, enzymes activity, stomatal conductance (G s), net photosynthetic rate (P n), transpiration rate (T r) and water-use efficiency (WUE). However, pretreatment with ethylene increased photosynthetic pigments content, enzymes activity and gas exchange parameters under both NW and WR3 treatments. The chlorophyll fluorescence results showed that the maximum quantum yield of PSII (F v/ F m) and actual photochemical efficiency of PSII (Φ PSII) remained no significant changes under the NW and WR1 treatments, while they were significantly reduced with an increase in waterlogging days followed by reoxygenation under WR2 and WR3 treatments. Exogenous ethylene inhibited F v/ F m and the non-photochemical quenching coefficient (NPQ), while enhanced Φ PSII and electron transfer efficiency (ETR) under WR2 treatments. Moreover, the accumulation of exogenous ethylene reduced photosynthetic ability. These findings provide insights into the role of ethylene in enhancing the tolerance of Z. armatum to reoxygenation stress, which could help mitigate the impact of continued climate change. This study evaluated the effects of ethylene pretreatment on the photosynthetic performance and tolerance of Zanthoxylum armatum seedlings to post-waterlogging reoxygenation stress. The results showed that reoxygenation stress decreased photosynthetic pigments content and enzymes activity, gas exchange parameters and chlorophyll fluorescence. However, ethylene pretreatment increased above indicators to enhance the tolerance to reoxygenation stress. These findings suggest that ethylene could be used to mitigate the impact of continued climate change on plant growth and development. [ABSTRACT FROM AUTHOR]

Malachite green (MG) is a common synthetic dye that raises environmental concerns. This study reveals that MG has inhibitory effects on the biochemistry and physiology of Eichhornia crassipes. Effects of different concentrations of MG on ROS-scavenging enzymes, α-amylase, proline, chlorophyll pigments, and various photosynthetic parameters of E. crassipes were investigated. Chlorophyll fluorescence analysis coupled with the JIP test showed the inhibitory effects of MG on biochemistry and photosynthetic potential depended on concentration and time. Up to 2 days of MG exposure, α-amylase and proline were upregulated with increasing MG concentration. When exposure time and concentration increased, all the parameters initially increased, then sharply declined. Chlorophyll content decreased with exposure time and concentration. Due to the slowing down of electron transport on the donor side brought on by MG exposure, P680+ builds up. According to an analysis of E. crassipes PSII activity, exposure to MG raises the proportion of inactive PSII reaction centres and active PSII centres. After increasing the exposure period (2, 4, and 6 days) and MG concentration (50, 100, 150, and 200 mg L−1), it decreased the absorption efficiency electron transport potential, maximal quantum yield of primary photochemistry, and the quantum yield of electron transport. These modifications led to a decline in the entire photosynthesis performance. The current research suggests that MG has detrimental effects on plants; therefore, the need for stringent regulations to prevent the release of dye-containing effluents into aquatic environments. Effluents from the dyeing industry discharged into aquatic habitats damage the ecosystem. Malachite green alters biochemical and physiological activities in Eichhornia crassipes. Chlorophyll a fluorescence emission analysis revealed that the donor of PSII was damaged. It disturbs the overall photosynthetic efficiency of plants. [ABSTRACT FROM AUTHOR]

In view of the importance of inorganic phosphate to plant growth and development, the role of phosphate transporters responsible for absorption and transportation in crops has attracted increasing attention. In this study, bioinformatics analysis and subcellular localisation experiment showed that GmPHT4;10 is a member of PHT4 subfamily of phosphate transporters and located in chloroplasts. The gene was induced by phosphate deficiency and drought, and was the highest in leaves. After GmPHT4;10 gene was replenished to AtPHT4;5 gene deletion mutant lines (atpht4;5), the phenotype of the transgenic lines was basically recovered to the level of wild-type, but there were significant differences in phosphate content and photosynthetic indicators between wild-type and revertant lines. Meanwhile, the difference of proline content and catalase activity between the two lines also indicated that GmPHT4;10 gene and its orthologous gene AtPHT4;5 were different in drought resistance and drought resistance mechanism. After overexpression of GmPHT4;10 gene in Arabidopsis thaliana , more phosphate and proline were accumulated in chloroplasts and catalase activity was increased, thus improving photosynthesis and drought resistance of plants. The results further supplement the cognition of PHT4 subfamily function, and provides new ideas and ways to improve photosynthesis by revealing the function of chloroplast phosphate transporter. GmPHT4;10 gene is a member of PHT4 subfamily of soybean (Glycine max) phosphate transporter gene family. GmPHT4;10 gene expression was induced by drought and low phosphorus stress. GmPHT4;10 gene has the physiological function of regulating chloroplast phosphorus content and improving plant drought resistance, but there are differences between GmPHT4;10 gene and its orthologous gene AtPHT4;5 in drought resistance mechanism. [ABSTRACT FROM AUTHOR]

Grain yield improvement in globally important staple crops is critical in the coming decades if production is to keep pace with growing demand; so there is increasing interest in understanding and manipulating plant growth and developmental traits for better crop productivity. However, this is confounded by complex cross-scale feedback regulations and a limited ability to evaluate the consequences of manipulation on crop production. Plant/crop modelling could hold the key to deepening our understanding of dynamic trait–crop–environment interactions and predictive capabilities for supporting genetic manipulation. Using photosynthesis and crop growth as an example, this review summarises past and present experimental and modelling work, bringing about a model-guided crop improvement thrust, encompassing research into: (1) advancing cross-scale plant/crop modelling that connects across biological scales of organisation using a trait dissection–integration modelling principle; (2) improving the reliability of predicted molecular–trait–crop–environment system dynamics with experimental validation; and (3) innovative model application in synergy with cross-scale experimentation to evaluate G × M × E and predict yield outcomes of genetic intervention (or lack of it) for strategising further molecular and breeding efforts. The possible future roles of cross-scale plant/crop modelling in maximising crop improvement are discussed. Significant improvements in the grain yield of globally important staple crops will be required in the coming decades, prompting genetic manipulation of plants for gains. But this path is impeded by limited understanding of molecular- and crop-scale interactions and insufficient field testing. To overcome these challenges, a model-guided crop improvement strategy can be employed, which capitalise on emerging cross-scale plant/crop models for unpacking complex agronomic traits and evaluating genetic manipulation targets, adding significant value to yield improvement efforts. [ABSTRACT FROM AUTHOR]

The physiological mechanisms of shade tolerance and trait plasticity variations under shade remain poorly understood in rice (Oryza sativa L.). Twenty-five genotypes of rice were evaluated under open and shade conditions. Various parameters to identify variations in the plasticity of these traits in growth irradiance were measured. We found wide variations in specific leaf weight (SLW) and net assimilation rate measured at 400 µmol m−2 s−1 photosynthetic photon flux density (PPFD; referred to as A 400) among the genotypes. Under shade, tolerant genotypes maintained a high rate of net photosynthesis by limiting specific leaf weight accompanied by increased intercellular CO2 concentration (C i) compared with open-grown plants. On average, net photosynthesis was enhanced by 20% under shade, with a range of 2–30%. Increased accumulation of biomass under shade was observed, but it showed no correlation with photosynthetic plasticity. Chlorophyll a / b ratio also showed no association with photosynthetic rate and yield. Analysis of variance showed that 11%, 16%, and 37% of the total variance of A 400, SLW, and C i were explained due to differences in growth irradiance. SLW and A 400 plasticity in growth irradiance was associated with yield loss alleviation with R 2 values of 0.37 and 0.16, respectively. Biomass accumulation was associated with yield loss alleviation under shade, but no correlation was observed between A 400 and leaf-N concentration. Thus, limiting specific leaf weight accompanied by increased C i rather than leaf nitrogen concentration might have allowed rice genotypes to maintain a high net photosynthesis rate per unit leaf area and high yield under shade. Plasticity in photosynthesis and specific leaf weight (SLW) are traits that allow shade-tolerant rice (Oryza sativa L.) genotypes to alleviate yield loss under shade. This was achieved by a reduction in SLW with increased intercellular CO2 concentration (C i). Leaf nitrogen did not influence photosynthesis rate under shade, but an accumulation of biomass was associated with yield. Limiting SLW with increased C i is the principal strategy to alleviate loss in photosynthesis and yield under low light intensity. [ABSTRACT FROM AUTHOR]

Low temperature (LT) during the grain-filling stage is an important factor that affects the source–sink relationship and leads to yield loss in maize (Zea mays L). In this study, field and pot trials were conducted to investigate the effects of LT during the grain-filling stage on leaf photosynthesis, antioxidant system, hormones, and grain yield of waxy maize cultivars Suyunuo 5 (S5) and Yunuo 7 (Y7). The results showed that LT treatment inhibited the chlorophyll biosynthesis and reduced the photosynthetic pigment levels during grain-filling stage. Ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase activities, photosynthetic rate, transpiration rate, and stomatal conductance decreased under LT treatment during the grain-filling stage. Furthermore, LT treatment increased the contents of malondialdehyde and reactive oxygen species, and decreased the activities of catalase, superoxide dismutase, peroxidase, and ascorbate peroxidase in the ear leaves, which accelerated the oxidative damage of leaf. The LT treatment also raised abscisic acid content and reduced indole acetic acid content in the ear leaves during grain-filling stage. The results of field and pot trials were verified by each other, but the field effect was greater than that of pot. Overall, LT treatment reduced the waxy maize dry matter accumulation after silking by affecting the physiological and biochemical processes of leaves, and ultimately decreased grain yield. Low temperature (LT) is an important abiotic stress that seriously affects the production and development of maize (Zea mays L). In this study, two waxy maize hybrids were selected and planted in two experimental environments to determine the dynamic changes in leaf photosynthesis, antioxidant system, hormones, and grain yield under post-silking LT stress. This study can be used as a reference for waxy maize to develop adaptation strategies under future climate conditions. [ABSTRACT FROM AUTHOR]

Manganese (Mn) plays an essential role in plant growth; however, excessive Mn is toxic to plants. Polygonum lapathifolium Linn. was tested as a novel Mn-hyperaccumulating species in our previous study, but the underlying mechanisms of this hyperaccumulation are poorly understood. A hydroponic experiment with (8 mmol L−1) and without additional Mn (CK) was established to explore the possible mechanisms through the effects on photosynthesis-related physiological characteristics and metabolomics. The results showed that additional Mn increased plant biomass, photosynthesis, and stomatal conductance related to increases in the effective photochemical quantum yield of photosystem II and relative electron transport rate (P < 0.05). The results from liquid chromatography–mass spectrometry revealed 56 metabolites differentially accumulated between the plants composing these two groups. Metabolites were enriched in 20 metabolic pathways at three levels (environmental information processing, genetic information processing, and metabolism), of which five metabolic pathways were associated with significant or extremely significant changes (P < 0.05). These five enriched pathways were ABC transporters (environmental information processing), aminoacyl-tRNA biosynthesis (genetic information processing), biosynthesis of amino acids , d-arginine and d-ornithine metabolism , and arginine biosynthesis (metabolism). Flavonoids may play a key role in Mn tolerance, as they accumulated more than 490-fold, and the relationship between flavonoids and Mn tolerance needs to be studied in the future. A hydroponic experiment with (8 mmol L−1) and without manganese was established to explore the mechanisms of manganese tolerance of Polygonum lapathifolium Linn via the effects on photosynthesis and metabolism. The results showed that manganese increased plant biomass, photosynthesis, and stomatal conductance. Moreover, among 1022 metabolites, 56 were significantly differentially accumulated, and flavonoids may be the key to the high tolerance of P. lapathifolium. The increased energy and photosynthates from photosynthesis were not allocated to amino acid synthesis. [ABSTRACT FROM AUTHOR]

Soil salinity is a growing problem in agriculture, plant growth regulators (PGRs) can regulate plant response to stress. The objective of this study was to evaluate the effects of exogenous 6-benzyladenine (6-BA) on photosynthetic capacity and antioxidant defences in watermelon (Citrullus lanatus L.) seedlings under NaCl stress. Two watermelon genotypes were subjected to four different treatments: (1) normal water (control); (2) 20 mg L−1 6-BA; (3) 120 mmol L−1 NaCl; and (4) 120 mmol L−1 NaCl + 20 mg L−1 6-BA. Our results showed that NaCl stress inhibited the growth of watermelon seedlings, decreased their photosynthetic capacity, promoted membrane lipid peroxidation, and lowered the activity of protective enzymes. Additionally the salt-tolerant Charleston Gray variety fared better than the salt-sensitive Zhengzi NO.017 variety under NaCl stress. Foliar spraying of 6-BA under NaCl stress significantly increased biomass accumulation, as well as photosynthetic pigment, soluble sugar, and protein content, while decreasing malondialdehyde levels, H2O2 content, and electrolyte leakage. Moreover, 6-BA enhanced photosynthetic parameters, including net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate; activated antioxidant enzymes, such as superoxide dismutase, catalase, and peroxidase; and improved the efficiency of the ascorbate-glutathione cycle by stimulating glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, as well as ascorbic acid and glutathione content. Principal component analysis confirmed that 6-BA improved salt tolerance of the two watermelon varieties, particularly Zhengzi NO.017, albeit through two different regulatory mechanisms. In conclusion, 6-BA treatment could alleviate NaCl stress-induced damage and improve salt tolerance of watermelons by regulating photosynthesis and osmoregulation, activating the ascorbate-glutathione cycle, and promoting antioxidant defences. The antioxidant and ascorbate-glutathione cycle of two types of salt-tolerant watermelon (Citrullus lanatus L.) seedlings under NaCl stress reveal an cytokinin regulated watermelon acclimation mechanism to the NaCl stress. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the phytotoxic effect of copper (Cu) and copper nanoparticles (CuONPs) and ameliorative potential of nitric oxide (NO) against these toxic materials in Sorghum vulgare Pers. seedlings. Data suggested that exposure of Cu and CuONPs significantly reduced growth, chlorophyll, carotenoids and protein in root and shoot, which coincided with increased Cu accumulation. However, addition of sodium nitroprusside (SNP, a donor of NO) lowered Cu and CuONPs mediated toxicity through restricting Cu accumulation and improving photosynthetic pigments and total soluble protein contents. Data further suggested that exposure of Cu and CuONPs significantly increased hydrogen peroxide (H2O2), superoxide radicals (O2•−), and malondialdehyde (MDA) contents. Enhanced level of oxidative stress severely inhibited the enzymatic activities of glutathione reductase (GR), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) but enhanced superoxide dismutase (SOD) and catalase (CAT) activity. However, addition of SNP positively regulated antioxidants enzymes activity, particularly the enzymes involved in the ascorbate-glutathione cycle to overcome Cu- and CuONPs-induced stress in Sorghum seedlings. Further, Cu and CuONPs enhanced accumulation of free proline through inducing Δ1-pyrroline-5-carboxylate synthetase (P5CS) activity while lowering the proline dehydrogenase (PDH) activity. However, addition of SNP reversed these responses. Therefore, overall results revealed that SNP has enough potential of reducing the toxicity of Cu and CuONPs in Sorghum seedlings through regulation of proline metabolism and activity of enzymes of the ascorbate-glutathione cycle. These findings can be employed in developing new resistant varieties of Sorghum having enhanced tolerance against Cu or CuONP stress and improved productivity. Enhancing crop productivity under the prevalent stressful environment is needed to meet global food demand. Copper (Cu) and copper oxide nanoparticles (CuONPs) pose adverse effects on Sorghum vulgare Pers. productivity. This study delineates that exogenous nitric oxide can mitigate their toxicity and improve the plant growth parameters. The findings of this research can be employed in developing new resistant varieties of sorghum having enhanced tolerance against Cu or CuONPs stress. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is a serious environmental contaminant that drastically limited the crop yields. Nitric oxide (NO) and spermine (Spm) portrayal significance in improving the plant tolerance against abiotic stresses. Therefore, we investigate the protective efficacy of seed priming with NO (100 μM) and/or Spm (0.01 mM) in minimising the Cr-induced toxic effects in rice (Oryza sativa L.) plants. Our outcomes revealed that Cr alone treatments (100 μM) notably reduced the seed germination rate, plant growth, photosynthetic apparatus, nutrients uptake and antioxidant defence system, but extra generation of reactive oxygen species (ROS). Interestingly, the combine applications of NO and Spm significantly reversed the Cr-induced toxic effects by reducing the Cr-accumulation, maintaining the nutrient balance, improving the germination indices, levels of photosynthetic pigments (chl a by 24.6%, chl b by 36.3%, chl (a + b) by 57.2% and carotenoids by 79.4%), PSII, photosynthesis gas exchange parameters and total soluble sugar (74.9%) by improving antioxidative enzyme activities. As a result, NO + Spm lowered the accumulation of oxidative markers (H2O2 by 93.9/70.4%, O2˙− by 86.3/69.9% and MDA by 97.2/73.7% in leaves/roots), electrolyte leakage (71.4% in leaves) and improved the plant growth traits. Based on these findings, it can be concluded that NO triggers Spm to minimise the Cr-accumulation and its adverse effects on rice plants. Additionally, combined treatments (NO + Spm) were more effective in minimising the Cr-induced toxic effects in comparison to NO and Spm alone treatments. Thus, co-exposure of NO and Spm may be utilised to boost rice tolerance under Cr stress conditions. Chromium (Cr) is a major constraint effecting the growth, yield and quality of rice (Oryza sativa L.). Priming with nitric oxide (NO) and Spermine (Spm) alleviates the negative effects of the Cr on the rice growth and development. Hence, the exogenous supply of NO and Spm possess great potential for the stress tolerance, and can be effectively used to prevent losses in crop plants under heavy metal stress. [ABSTRACT FROM AUTHOR]

In Qinghai-Tibet Plateau, crops are commonly subjected to freeze–thaw and salt stress factors simultaneously, and allelopathy is common, which affects the growth of highland barley (Hordeum vulgare L.), the largest food crop in Tibet. In order to explore the effects of artemisinin, salt and freeze–thaw (FAS) stress on physiological characteristics of highland barley seedlings, hydroponic experiment was carried out with the addition of 20 mg/L artemisinin and 150 mM NaCl as well as the simulation of freeze–thaw environment. The results suggested that under combined stress, the soluble protein content in combined stresses of artemisinin, FAS increased by 97.8%, the variation of relative conductivity in FAS group was lower than that in combined salt and freeze–thaw stress (FS), the relative water content decreased significantly (P < 0.05), the malondialdehyde (MDA), H2O2 and soluble sugar content in FAS group accumulated but less than those in FS group, and the superoxide dismutase (SOD) activity in combined artemisinin and freeze–thaw stress (FA) and FAS groups decreased. In addition, after freeze–thaw treatment, photosynthesis was weakened, and internal CO2 conentration (C i) in FAS group significantly decreased (P < 0.05). This study proved that appropriate amount of artemisinin can alleviate the damage of salt and freeze–thaw stress on barley seedlings. Freeze–thaw and NaCl stress limit plant growth. We focus on the effect of combined stress on seedlings of highland barley (Hordeum vulgare L.). Appropriate concentration of artemisinin can enhance the resistance to adverse environment. [ABSTRACT FROM AUTHOR]

Highland barley (Hordeum vulgare L.), as the dominant crop on the Qinghai-Tibetan Plateau, is a typical representative of plants adapted to extreme environmental conditions. However, the harsh environment, severe salinisation and frequent freezing and thawing in the Qinghai-Tibetan Plateau are main limiting factor for crop growth in this region. The physiological response of highland barley to salinisation and freeze–thaw stresses was studied in this paper. Under the combined stresses of 60 mmol/L NaCl·60 mmol/L NaHCO3 and freeze–thaw cycles (10, −5, and 10°C), the changes in the relative moisture content, relative electrical conductivity, soluble protein, malondialdehyde (MDA) and photosynthetic indices Pn and E in seedling leaves of eight groups of treatments (CK, S, A, S-A, CK (FT), S (FT), A (FT), and S-A (FT)) were analysed. Results showed that a single stress did not cause a change in the MDA content. All of the combined stresses in S-A, CK (FT), S (FT), A (FT), and S-A (FT) treatments increased the MDA content of barley seedlings, and the MDA content of S-A (FT) reached 28.438 at T2 (−5°C) μmol/g. During the freeze–thaw cycle, the cell membrane of seedlings was damaged more seriously by alkali stress, which showed a significant increase in relative conductivity. The relative moisture content value of seedlings was more than 100% because the seedlings could absorb more moisture due to mechanical injury. The protein content of osmoregulatory substances in highland barley seedlings increased with increasing stress, indicating resistance to stress. Moreover, the effect of freeze–thaw stress on photosynthesis was more significant. The changes in indices proved that an appropriate amount of salt stress could improve the resistance of the plant cell membrane. Alkali stress had a significant effect on the growth of highland barley seedlings. Freezing and thawing can aggravate the damage of saline–alkali stress to highland barley seedlings, resulting in changes in the biological membrane permeability and photosynthesis of seedlings. The fluctuation of osmoregulation substance content confirmed that highland barley seedlings had a certain degree of stress resistance. Freeze–thaw cycles will aggravate the damage of land salinisation to highland barley seedlings. To better reduce the impact and loss of land salinisation and freeze–thaw disasters on agriculture in the Qinghai-Tibetan Plateau, priority should be given to solving freeze–thaw stress in the process of grain production. Highland barley (Hordeum vulgare L.) is one of the important food crops for Tibetans. However, the environment in the Qinghai-Tibet Plateau is challenging for plant growth with combined stresses of saline–alkali and freeze–thaw affecting grain yield and quality. Research shows that the freeze–thaw cycle aggravate the damage of saline–alkali stress to highland barley seedlings, affecting biofilm permeability, osmotic adjustment and seedling photosynthesis. The results of this study will provide guidance and suggestions for improving crop production. [ABSTRACT FROM AUTHOR]

Low temperature is one of the major environmental stresses that limit crop growth and grain yield in wheat (Triticum aestivum L.). Drought priming at the vegetative stage could enhance wheat tolerance to later cold stress; however, the transgenerational effects of drought priming on wheat offspring's cold stress tolerance remains unclear. Here, the low temperature responses of offspring were tested after the parental drought priming treatment at grain filling stage. The offspring plants from parental drought priming treatment had a higher abscisic acid (ABA) level and lower osmotic potential (Ψo) than the control plants under cold conditions. Moreover, parental drought priming increased the antioxidant enzyme activities and decreased hydrogen peroxide (H2O2) accumulation in offspring. In comparison to control plants, parental drought priming plants had a higher ATP concentration and higher activities of ATPase and the enzymes involved in sucrose biosynthesis and starch metabolism. The results indicated that parental drought priming induced low temperature tolerance in offspring by regulating endogenous ABA levels and maintaining the redox homeostasis and the balance of carbohydrate metabolism, which provided a potential approach for cold resistant cultivation in wheat. Parental drought priming induced low temperature tolerance in wheat (Triticum aestivum L.) offspring. Offspring from parental drought priming had a better redox homeostasis under low temperature. Parental drought priming promoted carbohydrate metabolism of offspring. [ABSTRACT FROM AUTHOR]

The Arabidopsis thaliana L. photoreceptor genes homologues in tomato (Solanum lycopersicum L.) genome were analysed using bioinformatic tools. The expression pattern of these genes under cold stress was also evaluated. Transcriptome analysis of the tomato sequence revealed that the photoreceptor gene family is involved in abiotic stress tolerance. They participate in various pathways and controlling multiple metabolic processes. They are structurally related to PAS, LIGHT-OXYGEN-VOLTAGE-SENSING (LOV), DNA photolyase, 5,10-methenyl tetrahydrofolate (MTHF), flavin-binding kelch F-box, GAF, PHY, Seven-bladed β-propeller and C27 domains. They also interact with flavin adenine dinucleotide (FAD), (5S)-5-methyl-2-(methylsulfanyl)-5-phenyl-3-(phenylamino)-3,5-dihydro-4H-imidazol-4-one (FNM) and Phytochromobilin (PΦB) ligands. These interactions help to create a cascade of protein phosphorylation involving in cell defence transcription or stress-regulated genes. They localisation of these gene families on tomato chromosomes appeared to be uneven. Phylogenetic tree of tomato and Arabidopsis photoreceptor gene family were classified into eight subgroups, indicating gene expression diversity. Morphological and physiological assessment revealed no dead plant after 4 h of cold treatment. All the plants were found to be alive, but there were some variations in the data across different parameters. Cold stress significantly reduced the rate of photosynthesis from 10.06 to 3.16 µmol m-2 s-1, transpiration from 4.6 to 1.3 mmol m-2 s-1, and stomatal conductance from 94.6 to 25.6 mmol m-2 s-1. The cold stressed plants also had reduced height, root/shoot length, and fresh/dry biomass weight than the control plants. Relative expression analysis under cold stress revealed that after 4 h, light stimulates the transcript level of Cry2 from 1.9 to 5.7 and PhyB from 0.98 to 6.9 compared to other photoreceptor genes. [ABSTRACT FROM AUTHOR]

Natural variability of stress tolerance in halophytic plants is of significance both ecologically and in view of identifying molecular traits for salt tolerance in plants. Using ecophysiological and proteomic analyses, we address these phenomena in two Tunisian accessions of the oilseed halophyte, Cakile maritima Scop., thriving on arid and semi-arid Mediterranean bioclimatic stages (Djerba and Raoued, respectively), with a special emphasis on the leaves. Changes in biomass, photosynthetic gas exchange and pigment concentrations in C. maritima plants treated with three salinity levels (0, 100 and 300 mM NaCl) were monitored for 1 month. Comparative two-dimensional gel electrophoresis (2-DE) revealed 94 and 56 proteins of differential abundance in Raoued and Djerba accessions, respectively. These salinity-responsive proteins were mainly related to photosynthesis and oxidative phosphorylation (OXPHOS). Although Djerba accession showed a lower biomass productivity, it showed a slightly higher CO2 assimilation rate than Raoued accession when salt-treated. Photosynthesis impairment in both accessions under salinity was also suggested by the lower abundance of proteins involved in Calvin cycle and electron transfer. A significant increase of protein spots involved in the OXPHOS system was found in Djerba accession, suggesting an increase in mitochondrial respiration for increased ATP production under saline conditions, whereas a lesser pronounced trend was observed for Raoued accession. The latter showed in addition higher abundance of proteins involved in photorespiration. Salt-challenged plants of Djerba also likely developed mechanisms for scavenging ROS in leaves as shown by the increase in superoxide dismutase and thioredoxin, while an opposite trend was found in Raoued. [ABSTRACT FROM AUTHOR]

Quantum dots are versatile fluorescent semiconductor nanocrystals with unique photophysical properties. They have been used in various research fields of biotechnology effectively for almost three decades including cell imaging, protein tracking, energy transfer, etc. With their great potential as energy donors or acceptors, quantum dots have also been used in many studies about altering growth rate and photosynthetic activity of photosynthetic organisms by manipulating their light harvesting capacity. In this review, effect of quantum dots on growth rate of photosynthetic organisms and light harvesting capacity of photosynthetic organisms were discussed in details together with toxic effects of cadmium-based and carbon-based quantum dots on photosynthetic organisms. In short, as one of the promising materials of nanotechnology, quantum dots have become one of the essential research topics in photosynthesis research area and will help researchers to manipulate natural photosynthesis in future. [ABSTRACT FROM AUTHOR]

R is one of the most commonly used analytical tools in the plant sciences. To identify key trends in general reported R use and patterns in photosynthesis research, we explored the frequency of R use in 2966 articles published in the 377 journals with 'photosynthesis' in the title from 2010 to 2019 using the Web of Science search. Solutions provided by each R package cited in the articles or online sources was recorded and classified. The percentage of research articles reporting R use increased linearly from 3.6% in 2010 to 12.5% in 2019. The three main categories of R package solutions were 'general statistical calculations and graph packages' (G); 'photosynthesis special-purpose packages' (S); and 'genetic and evolutionary packages' (E). The top five R packages cited were nlme (G), lme4 (G), multcomp (G), plantecophys (S), and ape (E). The increasing popularity of R use in photosynthesis research is due to its user-friendly and abundant open-source codes online for handling specific issues, particularly in fitting photosynthesis models. These findings are limited by the number of articles and online sources, but they reveal a significant increase in usage in photosynthesis research over the past decade and have a bright prospect in the future. [ABSTRACT FROM AUTHOR]

This study documents the first validation of the suitability of the most common parameters and protocols used in marine ecophysiology to characterise photosynthesis by means of chlorophyll a fluorescence tools. We demonstrate that the effective yield of PSII (ΔF/Fm') is significantly underestimated when using short inductions times (≤1 min) following the rapid light curve protocol (RLC). The consequent electron transport rates (ETR) underestimations are species-specific and highly variable with irradiance and the photoacclimatory condition of the sample. Our analysis also questions the use of relative descriptors (relETR), as they not only overestimate photosynthesis, but overlook one of the fundamental components of the photosynthetic response: light absorption regulation. Absorptance determinations were fundamental to characterise the ETR response of low-pigmented seagrass leaves, and also uncovered relevant differences between two coral species and the accclimatory response of a cultured dinoflagellate to temperature. ETR and oxygen evolution determinations showed close correlations for all organisms tested with the expected slope of 4 e- per O2 molecule evolved, when correct photosynthesis inductions and light absorption determinations were applied. However, ETR curves cannot be equated to conventional photosynthetic response to irradiance (P vs E ) curves, and caution is needed when using ETR to characterise photosynthesis rates above photosynthesis saturation (Ek). This validation strongly supports the utility of fluorescence tools, underlining the need to correct two decades of propagation of erroneous concepts, protocols and parameters in marine eco-physiology. We aim also to emphasise the importance of optical descriptions for understanding photosynthesis, and for interpreting fluorescence measurements. In combination with conventional gross photosynthesis (GPS) approaches, optical characterisations open an extraordinary opportunity to determine two central parameters of photosynthesis performance: the quantum yield (φmax) of the process and its minimum quantum requirements (1/φmax). The combination of both approaches potentiates the possibilities of chlorophyll a fluorescence tools to characterise marine photosynthesis biodiversity. [ABSTRACT FROM AUTHOR]

In contrast to oxygenic photosynthesis, true anoxygenic photosynthesis is not associated with O2 evolution originated from water photolysis but still converts light energy to that of the phosphoanhydride bonds of ATP. In a narrow sense, anoxygenic photosynthesis is mainly known as to be related to the purple and green sulfur bacteria, but in a broad sense, it also occurs in the vascular plants. The portion of photosynthetic water photolysis that is compensated by the processes of O2 uptake (respiration, photorespiration, Mehler cycle, etc.) may be referred to as 'quasi' anoxygenic photosynthesis. Photoacoustic method allows for the separate detection of photolytic O2 at frequencies of measuring light about 20-40 Hz, whereas at 250-400 Hz, it detects the photochemical energy storage. We have developed a fast-Fourier transform photoacoustic method enabling measurements of both these signals simultaneously in one sample. This method allows to calculate oxygenic coefficients, which reflect the part of photochemically stored light energy that is used for the water photolysis. We show that the true anoxygenic photosynthesis in Ailanthus altissima Mill. leaves reached very high levels under low light, under moderate light at the beginning of the 1-h period, and at the end of the 40-min period under saturating light. [ABSTRACT FROM AUTHOR]

Photosynthesis occurs mainly in plant leaves and is a fundamental process in the global carbon cycle and in crop production. The exploitation of natural genetic variation in leaf photosynthetic capacity is a promising strategy to meet the increasing demand for crops. The present study reports the newly developed photosynthesis measurement system 'MIC-100,' with a higher throughput for measuring instantaneous photosynthetic rate in the field. MIC-100 is established based on the closed system and directly detects the CO2 absorption in the leaf chamber. The reproducibility, accuracy, and measurement throughput of MIC-100 were tested using soybean (Glycine max L. (Merr.)) and rice (Oryza sativa L.) grown under field conditions. In most cases, the coefficient of variance (CV) for repeatedmeasurements of the same leaf was less than 0.1. The photosynthetic rates measured with the MIC-100 model showed a significant correlation (R² = 0.93-0.95) with rates measured by a widely used gas-exchange system. The measurement throughput of the MIC-100 is significantly greater than that of conventional open gas-exchange systems under field conditions. Although MIC-100 solely detects the instantaneous photosynthetic rate under a given environment, this study demonstrated that the MIC-100 enables the rough evaluation of leaf photosynthesis within the large-scale plant populations grown in the field. [ABSTRACT FROM AUTHOR]

Wah Soon (Fred) Chow has been a major contributor to photosynthesis research since the late 20th century. Fred, a quiet, gentle, smart and prolific writer, has contributed to our understanding of thylakoid structure, cyclic electron flow and the development of novel methods for phenotyping plants. However, a third of his productivity centres on the understanding of photoinhibition and photoprotection, which we honour herein. We give a brief biographical account of his academic trajectory, followed by a chronological and conceptual summary of his contributions to the field of photodamage and photoprotection. We thereby hope to introduce the work of Fred to young readers and non-experts in the field of photoinhibition. [ABSTRACT FROM AUTHOR]

Severe water stress is responsible for reducing plant growth and reproduction. This study aimed to evaluate the physiological and biochemical mechanisms associated with the tolerance of two genotipes of bahiagrass (Paspalum notatum Flügge) with different ploidy level to water deficit and flooding at the reproductive stage. Photosynthetic performance of diploid and tetraploid plants was not affected by flooding. In contrast, the water deficit decreased stomatal conductance, increased leaf temperature, and resulted in a decrease in the assimilation rate of the two genotypes. Despite the greater activities of antioxidant enzymes, flooded roots accumulated hydrogen peroxide and malondialdehyde. Roots of plants exposed to water deficit maintained an accumulation of biomass similar to that of control plants; however, with higher levels of total phenol content, total soluble sugars and proline. Diploid plants subjected to flooding had more inflorescences, however, the drought reduced the total number of filled florets per plant. Less starch degradation allows the maintenance and recovery of biomass in the tetraploid genotype, which allows it to maintain its reproductive performance even under drought conditions. Overall, the synthesis of osmoprotectants and activation of antioxidant machinery are important strategies in the tolerance of bahiagrass to water stress at the reproductive stage. [ABSTRACT FROM AUTHOR]

Harvesting fruit from horticultural species causes a down-regulation of photosynthesis but some species can recover after harvest. The objective of this study was to assess the hypothesis that the impact of fruit removal on the photosynthetic performance of Shiraz grapevines, in relation to CO2 concentration and leaf temperature, would contribute to a depreciation in photosynthetic assimilation. To assess this hypothesis, vines that were continuously vegetative were compared with vines that were harvested when fruit were ripe. These fruiting vines had higher rates of CO2-limited photosynthesis at all leaf temperatures compared to vegetative vines before harvest but after, photosynthetic rates were highest in vegetative vines. There were few treatment differences in CO2-saturated photosynthesis before harvest but after, below about 30°C, the harvested vines had higher photosynthesis than the vegetative vines. Maximum rates of ribulose 1,5 bisphosphate (RuBP) carboxylation and regeneration and responses to temperature were unaffected by differences in sink demand but after harvest, maximum rates increased, but markedly more in the vegetative vines, especially at higher temperatures. This conformed to higher photosynthetic rates in the vegetative vines. There were no sink demand effects on chlorophyll a fluorescence, consistent with the evidence that the fruit sink removal probably affected Rubisco activity and performance. The conclusion that sink removal caused a depreciation in photosynthesis was sustained but the temperature had a strong modulating effect through both stomatal and non-stomatal limitations driving the depreciation in assimilation. What was less clear was why assimilation of continuously vegetative vines increased during the harvest time when there were no apparent changes in sink demand. The hypothesis that fruit removal affected photosynthetic performance of Shiraz grapevines was undertaken by comparing recently harvested and continuously vegetative vines. Fruiting vines had higher rates of CO2-limited photosynthesis compared to vegetative vines before harvest but after, photosynthetic rates were highest in vegetative vines. Sink removal caused a sustained depreciation in photosynthesis. Why assimilation of continuously vegetative vines increased during the harvest time when there were no apparent changes in sink demand was not resolved. [ABSTRACT FROM AUTHOR]

Photosynthesis in wheat (Triticum aestivum L.) pericarps may contribute appreciably to wheat grain yield. Consequently, we investigated the temporal variation of traits related to photosynthesis and sucrose metabolism in the pericarps and flag leaves of three wheat genotypes, Huandoy, Amurskaja 75 and Greece 25, which are reported to differ in expression of genes related to the C4 pathway in wheat grain. Significant site-specific, genotypic and temporal variation in the maximum carboxylation rate (Vc max) and maximum rates of electron transport (J max) (biological capacity of carbon assimilation) were observed early in ontogeny that dissipated by late grain filling. Although the transcript abundance of rbcS and rbcL in flag leaves was significantly higher than in the pericarps, in line with their photosynthetic prominence, both organ types displayed similar expression patterns among growth stages. The higher N concentrations in the pericarps during grain enlargement suggest increased Rubisco; however, expression of rbcS and rbcL indicated the contrary. From heading to 14 days post-anthesis, wheat pericarps exhibited a strong, positive correlation between biological capacity for carbon assimilation and expression of key genes related to sucrose metabolism (SPS1 , SUS1 and SPP1). The strong correlation between spike dry weight and the biological capacity for carbon assimilation along with other findings of this study suggest that metabolic processes in wheat spikes may play a major role in grain filling, total yield and quality. Recent findings raise the possibility of having differences of photosynthetic pathways at different organs within the same plant. Wheat (Triticum aestivum L.) leaves play a dominant role in photosynthesis at early grain filling. However, spike photosynthesis overtakes leaves during late grain filling and photosynthesis in wheat spikes may contribute appreciably to grain yield and quality. Hence, Investigation of site-specific and temporal variation of photosynthesis in critical food crops is important to increase the crop productivity. [ABSTRACT FROM AUTHOR]

To examine the interactive effect of temperature and photon flux density (PFD) on growth dynamics and gas exchange of young Vitis vinifera L. cv. Shiraz vines, a controlled environment study was conducted by exposing vines to two different temperatures combined with either high or low PFD. Shoot growth was accelerated and the phyllochron of Shiraz leaves was hastened in the low temperature (25/12°C) × low PFD condition (350 μmol m−2 s−1). In early emerging leaves, leaf area was responsive to temperature whereas in later emerging leaves it was dependent on light intensity. The high temperature (32/20°C) × high PFD (700 μmol m−2 s−1) treatment delayed internode extension of early emerging internodes. However, low temperature × high PFD increased leaf gas exchange across the different growth stages. The net shoot carbon balance was greater for the low temperature × high PFD treatment. Dry matter accumulation was also greater in early emerging internodes irrespective of treatment. These results on young Shiraz vines indicate that 25°C is favourable to 32°C, and some growth characteristics are accelerated at low PFD while others favour higher PFD. This study describes the effects of temperature and light combination on young Vitis vinifera L. cv. Shiraz vines. The low temperature and low or high light conditions are favourable for growth characters of young vegetative Shiraz vines. However, high temperature and high light conditions are detrimental. [ABSTRACT FROM AUTHOR]

This study investigated: (1) the effects of various concentrations of melatonin (MT) and Ca2+; and (2) the impact of crosstalk between these signal molecules on photosynthesis and salt tolerance of Dracocephalum kotschyi Boiss. Results indicated that 5 mM CaCl2, as well as 100 μM MT were the best concentrations for increasing shoot dry weight, leaf area, SPAD index, maximum quantum efficiency of photosystem II (F v/ F m), and decreasing malondialdehyde content under salinity stress. The impact of MT on growth and photosynthesis was closely linked to its effect on enhancing antioxidant enzyme activities in leaves. Application of p-chlorophenylalanine, as an inhibitor of MT biosynthesis, negated the impacts of MT on the aforementioned attributes. Salinity and MT boosted cytosolic Ca2+ concentration. Exogenous MT, as well as Ca2+, enhanced tolerance index, membrane stability, leaf area, the content of chlorophyll (Chl) a , Chl b , and carotenoids (Car), F v/ F m, and stomatal conductance under salinity stress. These impacts of MT were eliminated by applying a calmodulin antagonist, a Ca2+ chelator and a Ca2+ channel blocker. These novel findings indicate that the MT-induced effects on photosynthetic parameters and salt-evoked oxidative stress were mediated through calcium/calmodulin (Ca2+/CaM) signalling. Melatonin and calcium are highly conserved signals involved in salt tolerance. Impact of individual application both signal molecules on photosynthesis has been well proven, but detail of interplay of between them on regulating photosynthesis under salt stress has been not studied. Thus, it was investigated in this research. Results showed that impact of melatonin on photosynthesis and reducing oxidative stress mediated through Ca/CAM signalling pathway. [ABSTRACT FROM AUTHOR]

Drought is one of the major environmental constraints threatening viticulture worldwide. Therefore, it is critical to reveal the molecular mechanisms underlying grapevine (Vitis vinifera L.) drought stress tolerance useful to select new species with higher tolerance/resilience potentials. Drought-tolerant Tunisian local grapevine cultivar Razegui was exposed to water deficit for 16 days. Subsequent proteomic analysis revealed 49 differentially accumulated proteins in leaves harvested on the drought-stressed vines. These proteins were mainly involved in photosynthesis, stress defence, energy and carbohydrate metabolism, protein synthesis/turnover and amino acid metabolism. Physiological analysis revealed that reduction of photosynthesis under drought stress was attributed to the downregulation of the light-dependent reactions, Calvin cycle and key enzymes of the photorespiration pathway. The accumulation of proteins involved in energy and carbohydrate metabolism indicate enhanced need of energy during active stress acclimation. Accumulation of protein amino acids seems to play a protective role under drought stress due to their osmoprotectant and ROS scavenging potential. Reduced protein synthesis and turnover help plants preserving energy to fight drought stress. Proteins related to stress defence might scavenge ROS and transmit the ROS signal as an oxidative signal transducer in drought-stress signalling. All of these original results represent valuable information towards improving drought tolerance of grapevine and promoting sustainable viticulture under climate change conditions. Drought is a major abiotic constraints that will have a strong negative impact on Mediterranean viticulture. Proteomic analysis of drought-tolerant Tunisian local grapevine (Vitis vinifera L.) cultivar Razegui revealed that water deficit affected many proteins, particularly those involved in photosynthesis, stress defence, energy and carbohydrate metabolism, protein synthesis/turnover and amino acid metabolism. The results have expanded our knowledge of the mechanisms by which grapevines respond to drought and may assist in designing and developing more drought-tolerant grapevines in the future. [ABSTRACT FROM AUTHOR]

Delayed canopy senescence or 'stay-green' (SG) trait in maize (Zea mays L.) could improve drought tolerance. Two field trials comparing four to six maize hybrids with different senescence rate were carried out at Buenos Aires, Argentina, varying water availability during the reproductive period. Green leaf area at maturity was related to kernel weight (r²= 0.94***) but its relationship with yield was weaker (r² = 0.51--53*) and post-silking dry matter remobilisation was negatively related with the SG trait (r²= 0.84**). Two additional experiments were carried out in 63 L pots by withholding irrigation in half of the pots after silking. The SG hybrid achieved lower root biomass at silking, a shallower root distribution and larger root growth in the post-silking period. Under drought conditions, stomatal conductance was lower in the SG hybrid but photosynthetic electron transport rate was higher. Higher post-silking dry matter assimilation in the SG hybrid was compensated for by higher dry matter remobilisation in the non-SG. Higher kernel number per plant in the non-SG hybrid with no ability to compensate for by higher kernel weight in the SG, resulted in slightly higher yields in the non-SG under drought. A water conservation strategy associated with a shallower root system could be linked to the SG trait, promoting faster water depletion at upper soil levels and reduced stomatal conductance at the leaf level but with no conclusive yield advantage. [ABSTRACT FROM AUTHOR]

Excessive UVB reaching the earth is a cause for concern. To decipher the mechanism concerning UVB resistance of plants, we studied the effects of UVB radiation on photosynthesis and metabolic profiling of Rhododendron chrysanthum Pall. by applying 2.3 W m-2 of UVB radiation for 2 days. Results showed that maximum quantum yield of PSII (Fv/Fm) and effective quantum yield of PSII (φPSII) decreased by 7.95% and 8.36%, respectively, following UVB exposure. Twenty five known metabolites were identified as most important by two different methods, including univariate and multivariate statistical analyses. Treatment of R. chrysanthum with UVB increased the abundance of flavonoids, organic acids, and amino acids by 62%, 22%, and 5%, respectively. UVB irradiation also induced about 1.18-fold increase in 11 top-ranked metabolites identified: five organic acids (D-2,3-dihydroxypropanoic acid, maleic acid, glyceric acid, fumaric acid and suberic acid), four amino acids (L-norleucine, 3-oxoalanine, L-serine and glycine), and two fatty acids (pelargonic acid and myristoleic acid). In addition, UVB irradiation increased the intermediate products of arginine biosynthesis and the TCA cycle. Taken together, the accumulation of flavonoids, organic acids, amino acids and fatty acids, accompanied by enhancement of TCA cycle and arginine biosynthesis, may protect R. chrysanthum plants against UVB deleterious effects. [ABSTRACT FROM AUTHOR]

The present study explored the effectiveness of SiO2 nanoparticles (NPs) as seed priming agent (15 mg L-1) to improve drought tolerance in the wheat cultivar HI 1544. Seed germination studies showed significant enhancement in the rate of seed germination, seedling growth and vigour, seed water uptake, and amylase activity in nanoprimed (NP) seeds compared with unprimed (UP) seeds. Pot experiments using wheat plants subjected to drought stress showed that SiO2 nanopriming enhanced the ability of wheat plants to withstand water deficit conditions by balancing the production of reactive oxygen species and the activity of enzymatic antioxidants like peroxidase, catalase, and superoxide dismutase. Investigations of photosynthetic parameters showed that under drought conditions, nanoprimed plants had a higher number of active reaction centres, high absorbance, trapping, and electron transport rates compared with unprimed plants. These results suggest the effects of silicon nanopriming in enhancing drought tolerance in wheat by alleviating drought induced inhibition of plant photosynthetic machinery and maintaining biochemical balance, ultimately resulting in an increase in biomass production. Results revealed the use of silicon oxide nanopriming to be a good option to increase drought tolerance in wheat plants. [ABSTRACT FROM AUTHOR]

Solar-induced chlorophyll (chl) fluorescence (SIF) has been shown to be positively correlated with vegetation photosynthesis, suggesting that it is a useful signal for understanding of environmental responses and spatial heterogeneity of photosynthetic activity at various scales from leaf to the globe. Photosynthesis is often inhibited in stressful environments (photoinhibition), but how photoinhibition influences the relationship between photosynthesis and chl fluorescence remains unclear. Here, I studied light energy allocation among photosynthesis, chl fluorescence and heat dissipation in photoinhibited leaves and tested whether photosynthesis in photoinhibited leaves can be evaluated from chl fluorescence and reflectance spectra in remote sensing. Chl fluorescence and reflection spectra were examined with the pulse amplified modulation (PAM) system and spectroradiometer, respectively. Photoinhibited leaves had lower photosynthetic rates and quantum yields of photochemistry (ΦP) and higher chl fluorescence yields. Consequently, photosynthesis was negatively correlated with chl fluorescence, which contrasts the positive relationships between photosynthesis and SIF observed in past remote sensing studies. This suggests that vegetation photosynthesis evaluated solely from chl fluorescence may be overestimated if the vegetation is dominated by severely photoinhibited leaves. When a model of energy allocation was applied, ΦP estimated from chl fluorescence and photochemical reflectance index (PRI) significantly correlated with the observed ΦP, suggesting that the model is useful to evaluate photosynthetic activities of photoinhibited leaves by remote sensing. [ABSTRACT FROM AUTHOR]

Pilea peperomioides Diels (Urticaceae) is a semi-succulent herbaceous species native to south-western China that has become popular in cultivation as an ornamental plant. To investigate whether this species possesses the capacity for CAM photosynthesis, measurements were made of CO2 gas exchange and titratable acidity in plants under both well-watered and water-deficit conditions. Plants were found to assimilate CO2 almost exclusively in the light via C3 photosynthesis. However, distinct transient reductions in the rate of net nocturnal CO2 release were consistently observed during the course of the dark period, and under water-deficit conditions one plant exhibited a brief period of net nocturnal CO2 uptake, providing unequivocal evidence of CAM activity. Furthermore, nocturnal increases in titratable acidity in both leaf laminas and petioles were observed in all plants exposed to wet–dry–wet cycles. This is the first report of CAM in the family Urticaceae. The results are discussed in relation to the phylogenetic position of Pilea and the partially shaded montane habitats in which this species is typically found. An updated list of all plant families currently known to contain species with CAM is presented. Measurements of CO2 gas exchange and titratable acidity revealed features of low-level CAM photosynthesis in Pilea peperomioides. This is the first report of CAM in the family Urticaceae. [ABSTRACT FROM AUTHOR]

Leaves in different positions respond differently to dynamic fluctuations in light availability, temperature and to multiple environmental stresses. The current hypothesis states that elevated atmospheric CO2 (e[CO2]) can compensate for the negative effects of water scarcity regarding leaf gas exchanges and coffee bean quality traits over the canopy vertical profile, in interactions with light and temperature microclimate during the two final stages of berry development. Responses of Coffea arabica L. were observed in the 5th year of a free air CO2 enrichment experiment (FACE) under water-limited rainfed conditions. The light dependent leaf photosynthesis curves (A /PAR) were modelled for leaves sampled from vertical profile divided into four 50-cm thick layers. e[CO2] significantly increased gross photosynthesis (A maxGross), the apparent quantum yield efficiency, light compensation point, light saturation point (LSP) and dark respiration rate (R d). As a specific stage response, considering berry ripening, all parameters calculated from A /PAR were insensitive to leaf position over the vertical profile. Lack of a progressive increase in A maxGross and LSP was observed over the whole canopy profile in both stages, especially in the two lowest layers, indicating leaf plasticity to light. Negative correlation of R d to leaf temperature (TL) was observed under e[CO2] in both stages. Under e[CO2], stomatal conductance was also negatively correlated with TL, reducing leaf transpiration and R d even with increasing TL. This indicated coffee leaf acclimation to elevated temperatures under e[CO2] and water restriction. The e[CO2] attenuation occurred under water restriction, especially in A and water use efficiency, in both stages, with the exception of the lowest two layers. Under e[CO2], coffee produced berries in moderate- and high light level layers, with homogeneous distribution among them, contrasted to the heterogeneous distribution under actual CO2. e[CO2] led to increased caffeine content in the highest layer, with reduction of chlorogenic acid and lipids under moderate light and to raised levels of sugar in the shaded low layer. The ability of coffee to respond to e[CO2] under limited soil water was expressed through the integrated individual leaf capacities to use the available light and water, resulting in final plant investments in new reproductive structures in moderate and high light level layers. In climate change scenarios, plants are exposed to drought, changing temperatures and elevated [CO2]. The raising levels of CO2 can partially mitigate the impact of drought and elevated temperature at the coffee leaf scale. Coffee plants integrate the individual leaf capacities to efficiently use light and water under climate stress. [ABSTRACT FROM AUTHOR]

Recent studies have suggested that predawn stomatal opening may enhance early-morning photosynthesis (A) and improve the relative growth rate of trees. However, the causality between night-time stomatal conductance, A , and tree growth is disputable because stomatal opening in darkness can be mediated by previous day photosynthate loads and might be a consequence of growth-related processes like dark respiration (R). To identify linkages between night-time leaf conductance (g l_night), A , R , and tree growth, we conducted an experiment in hybrid aspen saplings grown under different air relative humidity (RH) conditions and previous day irradiance level (IR_pday). Predawn leaf conductance (g l_predawn) depended on RH, IR_pday and R (P < 0.05), whereas early-morning gross A (A gross_PAR500) depended on IR_pday and g l_predawn (P < 0.001). Daytime net A was positively related to A gross_PAR500 and leaf [N] (P < 0.05). Tree diameter and height increment correlated positively with g l at the beginning and middle of the night (P < 0.05) but not before dawn. Although our results demonstrate that g l_night was related to tree growth, the relationship was not determined by R. The linkage between g l_predawn and A gross_PAR500 was modified by IR_pday, indicating that daily CO2 assimilation probably provides feedback for stomatal opening before dawn. Although recent studies have proposed that high predawn stomatal conductance may enhance photosynthesis and growth of plants, the causality of this linkage is disputable. Our results suggest that night-time processes strongly depend on previous day light availability and the relationship between night-time stomatal conductance and tree growth characteristics are not directly related to predawn stomatal opening. Our findings indicate that daily CO2 assimilation probably provides feedback for stomatal opening before dawn. [ABSTRACT FROM AUTHOR]

Photosynthesis acclimation to high temperature differs among and within species. Grapevine intra-specific variation in photosynthetic acclimation to elevated temperature has been scarcely assessed. Our objectives were to (i) evaluate the mechanisms underlying long-term acclimation of photosynthesis to elevated temperature in grapevine, and (ii) determine whether these responses are similar among two varieties. A warming experiment with well irrigated Grenache and Syrah field-grown plants was performed during two growing seasons comparing plants exposed at ambient temperature (control) with plants in open-top chambers (heating) that increased mean air temperature between 1.5 and 3.6°C. Photosynthetic acclimation was assessed through the response of net assimilation (An), Rubisco carboxylation rate (Vcmax) and electron transport rate (Jmax), at leaf temperatures from 20 to 40°C. Our results evidenced different mechanisms for photosynthetic acclimation to elevated temperature. Compared with control, Grenache heated increased An, maintaining higher Vcmax and Jmax at temperatures above 35°C. By contrast, Syrah heated and control presented similar values of An, Vcmax and Jmax, evidencing an adjustment of photosynthesis without increasing C assimilation. Both varieties increased the optimum temperature for An, but to a lesser extent when growth temperature was higher. Our study provides evidence that grapevine varieties present different acclimation mechanisms to expected warming. [ABSTRACT FROM AUTHOR]

Rice undergoes leaf senescence accompanied with grain filling when the plants reach the end of their temporal niche, and a delay in leaf senescence ultimately improves the yield and quality of grain. To estimate the decline in photosynthesis during leaf senescence and to find an efficient and useful tool to identify rice genotypes with a longer duration of active photosynthesis, we examined PSII photosynthetic activity in the flag leaves of japonica rice Shennong265 (SN265) and Beigeng3 (BG3) during leaf senescence using chlorophyll a fluorescence kinetics. The results show that inhibition occurred in the electron transport chains, but the energetic connectivity of PSII units was not affected as dramatically during leaf senescence. PSII reaction centres (RCs) were transformed into 'silent RCs,' and the chlorophyll content decreased during leaf senescence. However the size of the 'economic' antennae increased. Further, the percentage of variation of the specific energy flux parameters can rationally be used to indicate leaf senescence from the perspective of energy balance. Although the performance indices were more sensitive than other functional and structural JIP-test parameters, they still did not serve as an indicator of crop yield. Natural senescence companied with grain filling influence rice yield, a longer active photosynthetic duration ultimately improving grain yield. In this work, we found an efficient and useful tool for estimate leaf senescence linked to active photosynthetic duration. This information will be of value for further rice breeding for enhanced yield. [ABSTRACT FROM AUTHOR]