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Leaf gas-exchange measurements are useful in assessing plant environmental responses. However, uncertainties in the leaf gas-exchange model potentially limit its application. The main challenge in the model-dependent calculations is to detect violations of assumptions. Here, we developed a system that integrates into one instrument the direct measurement of leaf intercellular CO2 concentration and the standard open-flow (OF) and novel open-diffusion (OD) systems for flux measurement. In the OD system, a gas-permeable membrane between the leaf ambient air and outside air creates CO2 and H2O differentials, rather than the air flow in the OF chamber. We measured hypostomatous and amphistomatous leaves of several species with different photosynthetic capacities [sunflower (Helianthus annuus), grape (Vitis vinifera), lemon (Citrus limon), and cherry (Prunus avium)]. The CO2 and H2O differentials in the OD system strictly depend on the flux measured by the OF system. The lower permeability of the membrane resulted in a larger differential per flux, indicating that the OD system can increase the resolution for a small flux. An analysis of the conductance model along with observations suggested that cuticle and leaf intercellular conductances and the unsaturation of leaf humidity contributed to discrepancies between the direct measurement and standard calculation. The combined system developed here provides an opportunity to address these overlooked concepts in leaf gas exchange. [ABSTRACT FROM AUTHOR]

The net CO2 assimilation (A) response to intercellular CO2 concentration (C i) is a fundamental measurement in photosynthesis and plant physiology research. The conventional A / C i protocols rely on steady-state measurements and take 15–40 min per measurement, limiting data resolution or biological replication. Additionally, there are several CO2 protocols employed across the literature, without clear consensus as to the optimal protocol or systematic biases in their estimations. We compared the non-steady-state Dynamic Assimilation Technique (DAT) protocol and the three most used CO2 protocols in steady-state measurements, and tested whether different CO2 protocols lead to systematic differences in estimations of the biochemical limitations to photosynthesis. The DAT protocol reduced the measurement time by almost half without compromising estimation accuracy or precision. The monotonic protocol was the fastest steady-state method. Estimations of biochemical limitations to photosynthesis were very consistent across all CO2 protocols, with slight differences in Rubisco carboxylation limitation. The A / C i curves were not affected by the direction of the change of CO2 concentration but rather the time spent under triose phosphate utilization (TPU)-limited conditions. Our results suggest that the maximum rate of Rubisco carboxylation (V c max), linear electron flow for NADPH supply (J), and TPU measured using different protocols within the literature are comparable, or at least not systematically different based on the measurement protocol used. [ABSTRACT FROM AUTHOR]

Concepts regarding the operation of the ascorbate–glutathione cycle and the associated water/water cycle in the processing of metabolically generated hydrogen peroxide and other forms of reactive oxygen species (ROS) are well established in the literature. However, our knowledge of the functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signalling pathways that regulate plant growth, development, and defence. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have 'moonlighting' functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signalling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate–glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways. [ABSTRACT FROM AUTHOR]

Legumes account for a significant proportion of plants in the terrestrial ecosystems. Nitrogen (N)-fixing capability of certain legumes is a pivotal trait that contributes to their ecological dominance. Yet, the functional traits and trait relationships between N-fixer and non-N-fixer legumes are poorly understood. Here, we investigated 27 functional traits associated with morphology, nutrients, hydraulic conductance and photosynthesis in 42 woody legumes (19 N-fixers and 23 non-N-fixers) in a common garden. Our results showed that N-fixers had higher specific leaf area, photosynthetic phosphorus (P)-use efficiency, leaf N, and iron concentrations on both area and mass basis, N/P ratio, and carbon (C) to P ratio, but lower wood density, area-based maximum photosynthetic rate (A a), photosynthetic N-use efficiency, leaf mass- and area-based P and molybdenum and area-based boron concentrations, and C/N ratio, compared with non-N-fixers. The mass-based maximum photosynthetic rate (A m), stomatal conductance (g s), intrinsic water-use efficiency (WUEi), mass- and area-based leaf potassium and mass-based boron concentrations, leaf hydraulic conductance (K leaf), and whole-shoot hydraulic conductance (K shoot) showed no difference between N-fixers and non-N-fixers. Significant positive associations between all hydraulic and photosynthetic trait pairs were found in N-fixers, but only one pair (K shoot– A a) in non-N-fixers, suggesting that hydraulic conductance plays a more important role in mediating photosynthetic capacity in N-fixers compared with non-N-fixers. Higher mass-based leaf N was linked to lower time-integrated g s and higher WUEi among non-N-fixer legumes or all legumes pooled after phylogeny was considered. Moreover, mass-based P concentration was positively related to A m and g s in N-fixers, but not in non-N-fixers, indicating that the photosynthetic capacity and stomatal conductance in N-fixers were more dependent on leaf P status than in non-N-fixers. These findings expand our understanding of the trait-based ecology within and across N-fixer and non-N-fixer legumes in tropics. [ABSTRACT FROM AUTHOR]

In the Mediterranean region, a reduction of annual precipitation and a longer and drier summer season are expected with climate change by the end of the century, eventually endangering forest survival. To cope with such rapid changes, trees may modulate their morpho-anatomical and physiological traits. In the present study, we focused on the variation in leaf gas exchange and different leaf morpho-anatomical functional traits of Quercus pubescens Willd. in summer using a long-term drought experiment in natura consisting of a dynamic rainfall exclusion system where trees have been submitted to amplified drought (AD) (~−30% of annual precipitation) since April 2012 and compared them with trees under natural drought (ND) in a Mediterranean forest. During the study, we analyzed net CO2 assimilation (An), stomatal conductance (gs), transpiration (E), water-use efficiency (WUE), stomatal size and density, density of glandular trichomes and non-glandular trichomes, thickness of the different leaf tissues, specific leaf area and leaf surface. Under AD, tree functioning was slightly impacted, since only An exhibited a 49% drop, while gs , E and WUE remained stable. The decrease in An under AD was regulated by concomitant lower stomatal density and reduced leaf thickness. Trees under AD also featured leaves with a higher non-glandular trichome density and a lower glandular trichome density compared with ND, which simultaneously limits transpiration and production costs. This study points out that Q. pubescens exhibits adjustments of leaf morpho-anatomical traits which can help trees to acclimate to AD scenarios as those expected in the future in the Mediterranean region. [ABSTRACT FROM AUTHOR]

This study aimed to reveal the mechanism and significance of wet canopy photosynthesis during and after rainfall in temperate coniferous ecosystems by evaluating the influence of abaxial leaf interception on wet canopy photosynthesis. We used the eddy covariance method in conjunction with an enclosed-path gas analyser to conduct continuous ecosystem CO2 flux observations in a Japanese cypress forest within the temperate Asian monsoon area over 3 years. The observation shows that wet-canopy CO2 uptake predominantly occurred during the post-rainfall canopy-wet period rather than the during-rainfall period. Then, the measured canopy-wet net ecosystem exchange was compared with the soil–vegetation–atmosphere transfer multilayer model simulations under different parameter settings of the abaxial (lower) leaf surface wet area ratio. The multilayer model predicted net ecosystem exchange most accurately when it assumed the wet area ratio of the abaxial surface was 50% both during and after rainfall. For the wet canopy both during and after rainfall, the model overestimated CO2 uptake when it assumed no abaxial interception in the simulation, but underestimated CO2 uptake when it assumed that the entire abaxial leaf surface was wet. These results suggest that the abaxial surface of the Japanese cypress leaf is only partly wet to maintain stomatal openness and a low level of photosynthesis. These results allow for an evaluation of the effect of rainfall on forest carbon circulation under a changing climate, facilitating an improvement of ecosystem carbon exchange models. [ABSTRACT FROM AUTHOR]

A circadian clock is an essential system that drives the 24-h expression rhythms for adaptation to day–night cycles. The molecular mechanism of the circadian clock has been extensively studied in cyanobacteria harboring the KaiC-based timing system. Nevertheless, our understanding of the physiological significance of the cyanobacterial circadian clock is still limited. In this study, we cultured wild-type Synechococcus elongatus PCC 7942 and circadian clock mutants in day–night cycles at different light qualities and found that the growth of the circadian clock mutants was specifically impaired during 12-h blue light/12-h dark (BD) cycles for the first time. The arrhythmic mutant kaiCAA was further analyzed by photosynthetic measurements. Compared with the wild type, the mutant exhibited decreases in the chlorophyll content, the ratio of photosystem I to II, net O2 evolution rate and efficiency of photosystem II photochemistry during BD cycles. These results indicate that the circadian clock is necessary for the growth and the maintenance of the optimum function of the photosynthetic apparatus in cyanobacteria under blue photoperiodic conditions. [ABSTRACT FROM AUTHOR]

The proton motive force (pmf) generated across the thylakoid membrane rotates the Fo-ring of ATP synthase in chloroplasts. The pmf comprises two components: membrane potential (∆Ψ) and proton concentration gradient (∆pH). Acidification of the thylakoid lumen resulting from ∆pH downregulates electron transport in the cytochrome b 6 f complex. This process, known as photosynthetic control, is crucial for protecting photosystem I (PSI) from photodamage in response to fluctuating light. To optimize the balance between efficient photosynthesis and photoprotection, it is necessary to regulate pmf. Cyclic electron transport around PSI and pseudo-cyclic electron transport involving flavodiiron proteins contribute to the modulation of pmf magnitude. By manipulating the ratio between the two components of pmf, it is possible to modify the extent of photosynthetic control without affecting the pmf size. This adjustment can be achieved by regulating the movement of ions (such as K+ and Cl−) across the thylakoid membrane. Since ATP synthase is the primary consumer of pmf in chloroplasts, its activity must be precisely regulated to accommodate other mechanisms involved in pmf optimization. Although fragments of information about each regulatory process have been accumulated, a comprehensive understanding of their interactions is lacking. Here, I summarize current knowledge of the network for pmf regulation, mainly based on genetic studies. [ABSTRACT FROM AUTHOR]

The highly phosphorylated nucleotide, guanosine tetraphosphate (ppGpp), functions as a secondary messenger in bacteria and chloroplasts. The accumulation of ppGpp alters plastidial gene expression and metabolism, which are required for proper photosynthetic regulation and robust plant growth. However, because four plastid-localized ppGpp synthases/hydrolases function redundantly, the impact of the loss of ppGpp-dependent stringent response on plant physiology remains unclear. We used CRISPR/Cas9 technology to generate an Arabidopsis thaliana mutant lacking all four ppGpp synthases/hydrolases and characterized its phenotype. The mutant showed over 20-fold less ppGpp levels than the wild type under normal growth conditions and exhibited leaf chlorosis and increased expression of defense-related genes as well as salicylic acid and jasmonate levels upon transition to nitrogen-starvation conditions. These results demonstrate that proper levels of ppGpp in plastids are required for controlling not only plastid metabolism but also phytohormone signaling, which is essential for plant defense. [ABSTRACT FROM AUTHOR]

Winterberry holly (Ilex verticillata [L.] A. Gray), a deciduous shrub producing glossy bright red berries, is a valuable ornamental and medicinal plant with good market prospects. However, the growth and development of I. verticillata are significantly affected by various stresses, and environmentally hazardous agrochemicals are often used to mitigate them. Trichoderma spp. ubiquitous soil-borne eco-friendly plant growth-promoting fungi, are potent biostimulants and biofertilizers and viable alternatives to agrochemicals for healthy and sustainable agriculture. In this study, the temporal efficacy of different dosages of the filamentous fungus Trichoderma guizhouense NJAU4742 in promoting morphophysiological responses of I. verticillata and the physicochemical properties and enzymatic activities of the substrate were investigated. Different concentrations of the strain T. guizhouense NJAU4742 spore suspension (C [0%], T1 [5%, v/m], T2 [10%, v/m] and T3 [15%, v/m]) were injected in the substrate contained in a pot in which 1-year-old I. verticillata was planted for temporal treatment (15, 45 and 75 days) under open-air conditions. The beneficial effects of T2 and/or T3 treatment for a long duration (75 days) were evident on the different root, aerial and photosynthetic traits; total contents of nitrogen (N), phosphorus (P) and potassium (K) in different tissues and the physicochemical properties of the substrate and its enzymatic activities (urease and invertase). Overall, the study revealed the potency of strain T. guizhouense NJAU4742 as a sustainable solution to improve the growth and development and ornamental value of I. verticillata. [ABSTRACT FROM AUTHOR]

Duckweeds span 36 species of free-floating aquatic organisms with body sizes ranging from 2 mm to 10 mm, where each plant body plan is reduced to a largely leaf-like structure. As an emerging crop, their fast growth rates offer potential for cultivation in closed systems. We describe a novel UK collection derived from low light (dLL) or high light (dHL) habitats, profiled for growth, photosynthesis, and photoprotection (non-photochemical quenching, NPQ) responses. Twenty-three accessions of three Lemna species and one Spirodela polyrhiza were grown under relatively low light (LL: 100 μmol m–2 s–1) and high light (HL: 350 μmol m–2 s–1) intensities. We observed broad within- and between-species level variation in photosynthesis acclimation. Duckweeds grown under HL exhibited a lower growth rate, biomass, chlorophyll, and quantum yield of photosynthesis. In HL compared with LL, carotenoid de-epoxidation state and NPQ were higher, whilst PSII efficiency (φPSII) and Chl a : b ratios were unchanged. The dLL plants showed relatively stronger acclimation to HL compared with dHL plants, especially Lemna japonica accessions. These achieved faster growth in HL with concurrent higher carotenoid levels and NPQ, and less degradation of chlorophyll. We conclude that these data support local adaptation to the light environment in duckweed affecting acclimation in controlled conditions. [ABSTRACT FROM AUTHOR]

Co-occurring heat and drought stresses challenge crop performance. Stomata open to promote evaporative cooling during heat stress, but close to retain water during drought stress, which resulted in complex stomatal regulation under combined heat and drought. We aimed to investigate stomatal regulation in leaves and flowers of perennial, indeterminate cultivars of tomatoes subjected to individual and combined heat and drought stress followed by a recovery period, measuring morphological, physiological, and biochemical factors involved in stomatal regulation. Under stress, stomata of leaves were predominantly affected by drought, with lower stomatal density and stomatal closing, resulting in significantly decreased photosynthesis and higher leaf temperature. Conversely, stomata in sepals seemed affected mainly by heat during stress. The differential patterns in stomatal regulation in leaves and flowers persisted into the recovery phase as contrasting patterns in stomatal density. We show that flower transpiration is regulated by temperature, but leaf transpiration is regulated by soil water availability during stress. Organ-specific patterns of stomatal development and abscisic acid metabolism mediated this phenomenon. Our results throw light on the dual role of stomata in heat and drought tolerance of vegetative and generative organs, and demonstrate the importance of considering flower surfaces in the phenotyping of stomatal reactions to stress. [ABSTRACT FROM AUTHOR]

One of the well-documented effects of regional warming in Antarctica is the impact on flora. Warmer conditions modify several leaf anatomical traits of Antarctic vascular plants, increasing photosynthesis and growth. Given that CO2 and water vapor partially share their diffusion pathways through the leaf, changes in leaf anatomy could also affect the hydraulic traits of Antarctic plants. We evaluated the effects of growth temperature on several anatomical and hydraulic parameters of Antarctic plants and assessed the trait co-variation between these parameters and photosynthetic performance. Warmer conditions promoted an increase in leaf and whole plant hydraulic conductivity, correlating with adjustments in carbon assimilation. These adjustments were consistent with changes in leaf vasculature, where Antarctic species displayed different strategies. At higher temperature, Colobanthus quitensis decreased the number of leaf xylem vessels, but increased their diameter. In contrast, in Deschampsia antarctica the diameter did not change, but the number of vessels increased. Despite this contrasting behavior, some traits such as a small leaf diameter of vessels and a high cell wall rigidity were maintained in both species, suggesting a water-conservation response associated with the ability of Antarctic plants to cope with harsh environments. [ABSTRACT FROM AUTHOR]

Photosynthesis plays a vital role in acclimating to and mitigating climate change, providing food and energy security for a population that is constantly growing, and achieving an economy with zero carbon emissions. A thorough comprehension of the dynamics of photosynthesis, including its molecular regulatory network and limitations, is essential for utilizing it as a tool to boost plant growth, enhance crop yields, and support the production of plant biomass for carbon storage. Photorespiration constrains photosynthetic efficiency and contributes significantly to carbon loss. Therefore, modulating or circumventing photorespiration presents opportunities to enhance photosynthetic efficiency. Over the past eight decades, substantial progress has been made in elucidating the molecular basis of photosynthesis, photorespiration, and the key regulatory mechanisms involved, beginning with the discovery of the canonical Calvin–Benson–Bassham cycle. Advanced chromatographic and mass spectrometric technologies have allowed a comprehensive analysis of the metabolite patterns associated with photosynthesis, contributing to a deeper understanding of its regulation. In this review, we summarize the results of metabolomics studies that shed light on the molecular intricacies of photosynthetic metabolism. We also discuss the methodological requirements essential for effective analysis of photosynthetic metabolism, highlighting the value of this technology in supporting strategies aimed at enhancing photosynthesis. [ABSTRACT FROM AUTHOR]

As climate change exacerbates drought stress in many parts of the world, understanding plant physiological mechanisms for drought survival is critical to predicting ecosystem responses. Stem net photosynthesis, which is common in arid environments, may be a drought survival trait, but whether the additional carbon fixed by stems contributes to plant hydraulic function and drought survival in arid land plants is untested. We conducted a stem light-exclusion experiment on saplings of a widespread North American desert tree species, Parkinsonia florida L. and after shading acclimation, we then subjected half of the plants to a drought treatment to test the interaction between light exclusion and water limitation on growth, leaf and stem photosynthetic gas exchange, xylem embolism assessed with micro-computed tomography and gravimetric techniques, and survival. Growth, stem photosynthetic gas exchange, hydraulic function and survival all showed expected reductions in response to light exclusion. However, stem photosynthesis mitigated the drought-induced reductions in gas exchange, xylem embolism (percent loss of conductivity, PLC) and mortality. The highest mortality was in the combined light exclusion and drought treatment, and was related to stem PLC and native sapwood-specific hydraulic conductivity. This research highlights the integration of carbon economy and water transport. Our results show that additional carbon income by photosynthetic stems has an important role in the growth and survival of a widespread desert tree species during drought. This shift in function under conditions of increasing stress underscores the importance of considering stem photosynthesis for predicting drought-induced mortality not only for the additional supply of carbon, but also for its extended benefits for hydraulic function. [ABSTRACT FROM AUTHOR]

Evergreen needleleaf forests (ENFs) play a sizable role in the global carbon cycle, but the biological and physical controls on ENF carbon cycle feedback loops are poorly understood and difficult to measure. To address this challenge, a growing appreciation for the stress physiology of photosynthesis has inspired emerging techniques designed to detect ENF photosynthetic activity with optical signals. This Overview summarizes how fundamental plant biological and biophysical processes control the fate of photons from leaf to globe, ultimately enabling remote estimates of ENF photosynthesis. We demonstrate this using data across four ENF sites spanning a broad range of environmental conditions and link leaf- and stand-scale observations of photosynthesis (i.e. needle biochemistry and flux towers) with tower- and satellite-based remote sensing. The multidisciplinary nature of this work can serve as a model for the coordination and integration of observations made at multiple scales. [ABSTRACT FROM AUTHOR]

Increasing evidence supports a major role for abiotic stress response in the success of plant polyploids, which usually thrive in harsh environments. However, understanding the ecophysiology of polyploids is challenging due to interactions between genome doubling and natural selection. Here, we investigated physiological responses, gene expression, and the epiphenotype of two related Dianthus broteri cytotypes—with different genome duplications (4× and 12×) and evolutionary trajectories—to short extreme temperature events (42/28 °C and 9/5 °C). The 12× cytotype showed higher expression of stress-responsive genes (SWEET1 , PP2C16 , AI5L3 , and ATHB7) and enhanced gas exchange compared with 4×. Under heat stress, both ploidies had greatly impaired physiological performance and altered gene expression, with reduced cytosine methylation. However, the 12× cytotype exhibited remarkable physiological tolerance (maintaining gas exchange and water status via greater photochemical integrity and probably enhanced water storage) while down-regulating PP2C16 expression. Conversely, 4× D. broteri was susceptible to thermal stress despite prioritizing water conservation, showing signs of non-stomatal photosynthetic limitations and irreversible photochemical damage. This cytotype also presented gene-specific expression patterns under heat, up-regulating ATHB7. These findings provide insights into divergent stress response strategies and physiological resistance resulting from polyploidy, highlighting its widespread influence on plant function. [ABSTRACT FROM AUTHOR]

The 13C isotope composition (δ13C) of leaf dry matter is a useful tool for physiological and ecological studies. However, how post-photosynthetic fractionation associated with respiration and carbon export influences δ13C remains uncertain. We investigated the effects of post-photosynthetic fractionation on δ13C of mature leaves of Cleistogenes squarrosa , a perennial C4 grass, in controlled experiments with different levels of vapour pressure deficit and nitrogen supply. With increasing leaf age class, the 12C/13C fractionation of leaf organic matter relative to the δ13C of atmosphere CO2 (ΔDM) increased while that of cellulose (Δcel) was almost constant. The divergence between ΔDM and Δcel increased with leaf age class, with a maximum value of 1.6‰, indicating the accumulation of post-photosynthetic fractionation. Applying a new mass balance model that accounts for respiration and export of photosynthates, we found an apparent 12C/13C fractionation associated with carbon export of –0.5‰ to –1.0‰. Different ΔDM among leaves, pseudostems, daughter tillers, and roots indicate that post-photosynthetic fractionation happens at the whole-plant level. Compared with ΔDM of old leaves, ΔDM of young leaves and Δcel are more reliable proxies for predicting physiological parameters due to the lower sensitivity to post-photosynthetic fractionation and the similar sensitivity in responses to environmental changes. [ABSTRACT FROM AUTHOR]

This article discusses the importance of phenotyping photosynthesis for crop improvement and breeding programs. The authors highlight the challenges of studying photosynthesis in natural conditions and the need for higher throughput tools to overcome these barriers. They discuss the use of controlled-environment systems and remote sensing methods, such as solar-induced fluorescence and laser/light-induced fluorescence transient, for phenotyping photosynthesis. The authors also mention the use of hand-held MultispeQ PAM fluorometers as affordable tools for field phenotyping. The article concludes by emphasizing the potential of photosynthetic phenotyping for driving yield improvement in crop breeding programs. [Extracted from the article]

We examined photosynthetic traits of pre-existing and newly developed flag leaves of four wheat genotypes grown in controlled-environment experiments. In newly developed leaves, acclimation of the maximum rate of net CO2 assimilation (A n) to warm nights (i.e. increased A n) was associated with increased capacity of Rubisco carboxylation and photosynthetic electron transport, with Rubisco activation state probably contributing to increased Rubisco activity. Metabolite profiling linked acclimation of A n to greater accumulation of monosaccharides and saturated fatty acids in leaves; these changes suggest roles for osmotic adjustment of leaf turgor pressure and maintenance of cell membrane integrity. By contrast, where A n decreased under warm nights, the decline was related to lower stomatal conductance and rates of photosynthetic electron transport. Decreases in A n occurred despite higher basal PSII thermal stability in all genotypes exposed to warm nights: T crit of 45–46.5 °C in non-acclimated versus 43.8–45 °C in acclimated leaves. Pre-existing leaves showed no change in A n–temperature response curves, except for an elite heat-tolerant genotype. These findings illustrate the impact of night-time warming on the ability of wheat plants to photosynthesize during the day, thereby contributing to explain the impact of global warming on crop productivity. [ABSTRACT FROM AUTHOR]

The production of ATP and NADPH by the light reactions of photosynthesis and their consumption by the Calvin–Benson–Bassham (CBB) cycle and other downstream metabolic reactions requires careful regulation. Environmental shifts perturb this balance, leading to photo-oxidative stress and losses in CO2 assimilation. Imbalances in the production and consumption of ATP and NADPH manifest themselves as transient instability in the chlorophyll fluorescence, P700, electrochromic shift, and CO2 uptake signals recorded on leaves. These oscillations can be induced in wild-type plants by sudden shifts in CO2 concentration or light intensity; however, mutants exhibiting increased oscillatory behaviour have yet to be reported. This has precluded an understanding of the regulatory mechanisms employed by plants to suppress oscillations. Here we show that the Arabidopsis pgr5 mutant, which is deficient in Proton Gradient Regulation 5 (PGR5)-dependent cyclic electron transfer (CET), exhibits increased oscillatory behaviour. In contrast, mutants lacking the NADH-dehydrogenase-like-dependent CET are largely unaffected. The absence of oscillations in the hope2 mutant which, like pgr5 , lacks photosynthetic control and exhibits high ATP synthase conductivity, ruled out loss of these photoprotective mechanisms as causes. Instead, we observed slower formation of the proton motive force and, by inference, ATP synthesis in pgr5 following environmental perturbation, leading to the transient reduction of the electron transfer chain and photosynthetic oscillations. PGR5-dependent CET therefore plays a major role in damping the effect of environmental perturbations on photosynthesis to avoid losses in CO2 fixation. [ABSTRACT FROM AUTHOR]

Photosynthesis drives plant physiology, biomass accumulation, and yield. Photosynthetic efficiency, specifically the operating efficiency of PSII (F q'/ F m'), is highly responsive to actual growth conditions, especially to fluctuating photosynthetic photon fluence rate (PPFR). Under field conditions, plants constantly balance energy uptake to optimize growth. The dynamic regulation complicates the quantification of cumulative photochemical energy uptake based on the intercepted solar energy, its transduction into biomass, and the identification of efficient breeding lines. Here, we show significant effects on biomass related to genetic variation in photosynthetic efficiency of 178 climbing bean (Phaseolus vulgaris L.) lines. Under fluctuating conditions, the F q'/ F m' was monitored throughout the growing period using hand-held and automated chlorophyll fluorescence phenotyping. The seasonal response of F q'/ F m' to PPFR (ResponseG:PPFR) achieved significant correlations with biomass and yield, ranging from 0.33 to 0.35 and from 0.22 to 0.31 in two glasshouse and three field trials, respectively. Phenomic yield prediction outperformed genomic predictions for new environments in four trials under different growing conditions. Investigating genetic control over photosynthesis, one single nucleotide polymorphism (Chr09_37766289_13052) on chromosome 9 was significantly associated with ResponseG:PPFR in proximity to a candidate gene controlling chloroplast thylakoid formation. In conclusion, photosynthetic screening facilitates and accelerates selection for high yield potential. [ABSTRACT FROM AUTHOR]

Carbonic anhydrase (CA) catalyzes the reversible CO2 hydration reaction that produces bicarbonate for phosphoenolpyruvate carboxylase (PEPC). This is the initial step for transmitting the CO2 signal in C4 photosynthesis. However, it remains unknown whether the maize (Zea mays L.) CA gene, ZmCA4 , plays a role in the maize photosynthesis process. In our study, we found that ZmCA4 was relatively highly expressed in leaves and localized in the chloroplast and the plasma membrane of mesophyll protoplasts. Knock-out of ZmCA4 reduced CA activity, while overexpression of ZmCA4 increased rubisco activity, as well as the quantum yield and relative electron transport rate in photosystem II. Overexpression of ZmCA4 enhanced maize yield–related traits. Moreover, ZmCA4 interacted with aquaporin ZmPIP2;6 in bimolecular fluorescence complementation and co-immunoprecipitation experiments. The double-knock-out mutant for ZmPIP2;6 and ZmCA4 genes showed reductions in its growth, CA and PEPC activities, assimilation rate and photosystem activity. RNA-Seq analysis revealed that the expression of other ZmCAs, ZmPIPs , as well as CO2 signaling pathway homologous genes, and photosynthetic-related genes was all altered in the double-knock-out mutant compared with the wild type. Altogether, our study's findings point to a critical role of ZmCA4 in determining photosynthetic capacity and modulating CO2 signaling regulation via its interaction with ZmPIP2;6, thus providing insight into the potential genetic value of ZmCA4 for maize yield improvement. [ABSTRACT FROM AUTHOR]

Background and Aims HCO3– can be a major carbon resource for photosynthesis in underwater environments. Here we investigate the underlying mechanism of uptake and membrane transport of HCO3– in submerged leaves of Hygrophila difformis , a heterophyllous amphibious plant. To characterize these mechanisms, we evaluated the sensitivity of underwater photosynthesis to an external carbonic anhydrase (CA) inhibitor and an anion exchanger protein inhibitor, and we attempted to identify components of the mechanism of HCO3– utilization. Methods We evaluated the effects of the external CA inhibitor and anion exchanger protein inhibitor on the NaHCO3 response of photosynthetic O2 evolution in submerged leaves of H. difformis. Furthermore, we performed a comparative transcriptomic analysis between terrestrial and submerged leaves. Key Results Photosynthesis in the submerged leaves was decreased by both the external CA inhibitor and anion exchanger protein inhibitor, but no additive effect was observed. Among upregulated genes in submerged leaves, two α-CAs, Hd α -CA1 and Hd α -CA2 , and one β-carbonic anhydrase, Hd β -CA1 , were detected. Based on their putative amino acid sequences, the α-CAs are predicted to be localized in the apoplastic region. Recombinant Hdα-CA1 and Hdβ-CA1 showed dominant CO2 hydration activity over HCO3– dehydration activity. Conclusions We propose that the use of HCO3– for photosynthesis in submerged leaves of H. difformis is driven by the cooperation between an external CA, Hdα-CA1, and an unidentified HCO3– transporter. [ABSTRACT FROM AUTHOR]

Intercropping improves resource utilization. Under wide–narrow-row maize (Zea mays) intercropping, maize plants are subjected to weak unilateral illumination and exhibit high photosynthetic performance. However, the mechanism regulating photosynthesis under unilateral weak light remains unknown. We investigated the relationship between photosynthesis and sugar metabolism in maize under unilateral weak light. Our results showed that the net photosynthetic rate (P n) of unshaded leaves increased as the level of shade on the other side increased. On the contrary, the concentration of sucrose and starch and the number of starch granules in the unshaded leaves decreased with increased shading due to the transfer of abundant C into the grains. However, sink loss with ear removal reduced the P n of unshaded leaves. Intense unilateral shade (40% to 20% normal light), but not mild unilateral shade (60% normal light), reduced grain yield (37.6% to 54.4%, respectively). We further found that in unshaded leaves, Agpsl , Bmy , and Mexl-like expression significantly influenced sucrose and starch metabolism, while Sweet13a and Sut1 expression was crucial for sugar export. In shaded leaves, expression of Sps1 , Agpsl , and Sweet13c was crucial for sugar metabolism and export. This study confirmed that unshaded leaves transported photosynthates to the ear, leading to a decrease in sugar concentration. The improvement of photosynthetic performance was associated with altered sugar transport. We propose a narrow-row spacing of 40 cm, which provides appropriate unilateral shade and limits yield reduction. [ABSTRACT FROM AUTHOR]

The photosynthesis-induced accumulation of reactive oxygen species in chloroplasts can lead to oxidative stress, triggering changes in protein synthesis, degradation, and the assembly/disassembly of protein complexes. Using shot-gun proteomics, we identified methyl viologen-induced changes in protein abundance in wild-type Arabidopsis and oxidative stress-hypersensitive fsd1-1 and fsd1-2 knockout mutants, which are deficient in IRON SUPEROXIDE DISMUTASE 1 (FSD1). The levels of proteins that are localized in chloroplasts and the cytoplasm were modified in all lines treated with methyl viologen. Compared with the wild-type, fsd1 mutants showed significant changes in metabolic protein and chloroplast chaperone levels, together with increased ratio of cytoplasmic, peroxisomal, and mitochondrial proteins. Different responses in proteins involved in the disassembly of photosystem II–light harvesting chlorophyll a / b binding proteins were observed. Moreover, the abundance of PATELLIN 4, a phospholipid-binding protein enriched in stomatal lineage, was decreased in response to methyl viologen. Reverse genetic studies using patl4 knockout mutants and a PATELLIN 4 complemented line indicate that PATELLIN 4 affects plant responses to oxidative stress by effects on stomatal closure. [ABSTRACT FROM AUTHOR]

Solar-induced chlorophyll fluorescence (SIF) provides an opportunity to rapidly and non-destructively investigate how plants respond to stress. Here, we explored the potential of SIF to detect the effects of elevated O3 on soybean in the field where soybean was subjected to ambient and elevated O3 throughout the growing season in 2021. Exposure to elevated O3 resulted in a significant decrease in canopy SIF at 760 nm (SIF760), with a larger decrease in the late growing season (36%) compared with the middle growing season (13%). Elevated O3 significantly decreased the fraction of absorbed photosynthetically active radiation by 8–15% in the middle growing season and by 35% in the late growing stage. SIF760 escape ratio (f esc) was significantly increased under elevated O3 by 5–12% in the late growth stage due to a decrease of leaf chlorophyll content and leaf area index. Fluorescence yield of the canopy was reduced by 5–11% in the late growing season depending on the f esc estimation method, during which leaf maximum carboxylation rate and maximum electron transport were significantly reduced by 29% and 20% under elevated O3. These results demonstrated that SIF could capture the elevated O3 effect on canopy structure and acceleration of senescence in soybean and provide empirical support for using SIF for soybean stress detection and phenotyping. [ABSTRACT FROM AUTHOR]

Climate change has universally affected the whole ecosystem in a unified manner and is known to have improbable effects on agricultural productivity and food security. Carbon dioxide (CO2) and temperature are the major environmental factors that have been shown to increase sharply during the last century and are directly responsible for affecting plant growth and development. A number of previous investigations have deliberated the positive effects of elevated CO2 on plant growth and development of various C3 crops, while detrimental effects of enhanced temperature on different crop plants like rice, wheat, maize and legumes are generally observed. A combined effect of elevated CO2 and temperature has yet to be studied in great detail; therefore, this review attempts to delineate the interactive effects of enhanced CO2 and temperature on plant growth, development, physiological and molecular responses. Elevated CO2 maintains leaf photosynthesis rate, respiration, transpiration and stomatal conductance in the presence of elevated temperature and sustains plant growth and productivity in the presence of both these environmental factors. Concomitantly, their interaction also affects the nutritional quality of seeds and leads to alterations in the composition of secondary metabolites. Elevated CO2 and temperature modulate phytohormone concentration in plants, and due to this fact, both environmental factors have substantial effects on abiotic and biotic stresses. Elevated CO2 and temperature have been shown to have mitigating effects on plants in the presence of other abiotic stress agents like drought and salinity, while no such pattern has been observed in the presence of biotic stress agents. This review focuses on the interactive effects of enhanced CO2 and temperature on different plants and is the first of its kind to deliver their combined responses in such detail. [ABSTRACT FROM AUTHOR]

Stem respiration (RS) substantially contributes to the return of photo assimilated carbon to the atmosphere and, thus, to the tree and ecosystem carbon balance. Stem CO2 efflux (ECO2) is often used as a proxy for RS. However, this metric has often been challenged because of the uncertain origin of CO2 emitted from the stem due to post-respiratory processes. In this Insight , we (i) describe processes affecting the quantification of RS, (ii) review common methodological approaches to quantify and model RS and (iii) develop a research agenda to fill the most relevant knowledge gaps that we identified. Dissolution, transport and accumulation of respired CO2 away from its production site, reassimilation of respired CO2 via stem photosynthesis and the enzyme phosphoenolpyruvate carboxylase, axial CO2 diffusion in the gas phase, shifts in the respiratory substrate and non-respiratory oxygen (O2) consumption are the most relevant processes causing divergence between RS and measured stem gas exchange (ECO2 or O2 influx, IO2). Two common methodological approaches to estimate RS, namely the CO2 mass balance approach and the O2 consumption technique, circumvent some of these processes but have yielded inconsistent results regarding the fate of respired CO2. Stem respiration modelling has recently progressed at the organ and tree levels. However, its implementation in large-scale models, commonly operated from a source-driven perspective, is unlikely to reflect adequate mechanisms. Finally, we propose hypotheses and approaches to advance the knowledge of the stem carbon balance, the role of sap pH on RS, the reassimilation of respired CO2, RS upscaling procedures, large-scale RS modelling and shifts in respiratory metabolism during environmental stress. [ABSTRACT FROM AUTHOR]

How plants use the carbon they gain from photosynthesis remains a key area of study among plant ecologists. Although numerous theories have been presented throughout the years, the field lacks a clear null model. To fill this gap, I have developed the first null model, or neutral theory, of plant carbon allocation using probability theory, plant biochemistry and graph theory at the level of a leaf. Neutral theories have been used to establish a null hypothesis in molecular evolution and community assembly to describe how much of an ecological phenomenon can be described by chance alone. Here, the aim of a neutral theory of plant carbon allocation is to ask: how is carbon partitioned between sinks if one assumes plants do not prioritize certain sinks over others? Using the biochemical network of plant carbon metabolism, I show that, if allocation was strictly random, carbon is more likely to be allocated to storage, defense, respiration and finally growth. This 'neutral hierarchy' suggests that a sink's biochemical distance from photosynthesis plays an important role in carbon allocation patterns, highlighting the potentially adaptive role of this biochemical network for plant survival in variable environments. A brief simulation underscores that our ability to measure the carbon allocation from photosynthesis to a given sink is unreliable due to simple probabilistic rules. While neutral theory may not explain all patterns of carbon allocation, its utility is in the minimal assumptions and role as a null model against which future data should be tested. [ABSTRACT FROM AUTHOR]

Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3− influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress. [ABSTRACT FROM AUTHOR]

Root pruning hinders the absorption and utilization of nutrients and water by seedlings in the short term. Arbuscular mycorrhizal fungi (AMF) are an important source of nutrient and water for seedlings except for the root system. However, the mechanism by which AMF affect the physiological growth of seedlings after root pruning has rarely been studied. In this study, a pot experiment was conducted through a three-compartment partition system to clarify the effects of Funneliformis mosseae (F. mosseae) strain BGC XJ07A on the physiological growth of root-pruned Robinia pseudoacacia seedlings. Five root pruning treatments (zero, one-fifth, one-fourth, one-third and one-half of the taproot length were removed) were applied to noninoculated seedlings and those inoculated with F. mosseae. The results showed that the presence of F. mosseae significantly increased the shoot and root biomasses, leaf photosynthetic rate, stomatal conductance and transpiration rate. The root projected area, root surface area, average root diameter, root density, root volume and number of root tips of the inoculated seedlings were higher than those without inoculation in all root pruning treatments. The root cytokinin, gibberellins and indole-3-acetic acid concentrations, but root abscisic acid concentration, were higher than those measured in the absence of inoculation in all root pruning treatments. Moreover, the changes in the root endogenous hormone concentrations of the seedlings were closely related to the root morphological development and seedling biomass. The AMF increased the soil available nitrogen, soil available phosphorus, soil available potassium and soil organic matter concentrations compared with the noninoculated treatment. These results indicate that AMF can alleviate the adverse effects of root pruning on the physiological growth of R. pseudoacacia and soil properties, and can provide a basis for AMF application to forest cultivation and the sustainable development of forest ecosystems. [ABSTRACT FROM AUTHOR]

This document is a correction to an article titled "Temperature sensitivity of detrital photosynthesis" published in the Annals of Botany. The original version of the manuscript contained errors in the in-text figure references and equations. These errors have been corrected in the document. The publisher apologizes for the mistakes and clarifies that they were not the fault of the authors. [Extracted from the article]

Background and Aims Kelp forests are increasingly considered blue carbon habitats for ocean-based biological carbon dioxide removal, but knowledge gaps remain in our understanding of their carbon cycle. Of particular interest is the remineralization of detritus, which can remain photosynthetically active. Here, we study a widespread, thermotolerant kelp (Ecklonia radiata) to explore detrital photosynthesis as a mechanism underlying temperature and light as two key drivers of remineralization. Methods We used meta-analysis to constrain the thermal optimum (T opt) of E. radiata. Temperature and light were subsequently controlled over a 119-day ex situ decomposition experiment. Flow-through experimental tanks were kept in darkness at 15 °C or under a subcompensating maximal irradiance of 8 µmol photons m−2 s−1 at 15, 20 or 25 °C. Photosynthesis of laterals (analogues to leaves) was estimated using closed-chamber oxygen evolution in darkness and under a saturating irradiance of 420 µmol photons m−2 s−1. Key Results T opt of E. radiata is 18 °C across performance variables (photosynthesis, growth, abundance, size, mass and fertility), life stages (gametophyte and sporophyte) and populations. Our models predict that a temperature of >15 °C reduces the potential for E. radiata detritus to be photosynthetically viable, hence detrital T opt ≤ 15 °C. Detritus is viable under subcompensating irradiance, where it performs better than in darkness. Comparison of net and gross photosynthesis indicates that elevated temperature primarily decreases detrital photosynthesis, whereas darkness primarily increases detrital respiration compared with optimal experimental conditions, in which detrital photosynthesis can persist for ≥119 days. Conclusions T opt of kelp detritus is ≥3 °C colder than that of the intact plant. Given that E. radiata is one of the most temperature-tolerant kelps, this suggests that photosynthesis is generally more thermosensitive in the detrital phase, which partly explains the enhancing effect of temperature on remineralization. In contrast to darkness, even subcompensating irradiance maintains detrital viability, elucidating the accelerating effect of depth and its concomitant light reduction on remineralization to some extent. Detrital photosynthesis is a meaningful mechanism underlying at least two drivers of remineralization, even below the photoenvironment inhabited by the attached alga. [ABSTRACT FROM AUTHOR]

Nucleotide limitation and imbalance is a well-described phenomenon in animal research but understudied in the plant field. A peculiarity of pyrimidine de novo synthesis in plants is the complex subcellular organization. Here, we studied two organellar localized enzymes in the pathway, with chloroplast aspartate transcarbamoylase (ATC) and mitochondrial dihydroorotate dehydrogenase (DHODH). ATC knock-downs were most severely affected, exhibiting low levels of pyrimidine nucleotides, a low energy state, reduced photosynthetic capacity and accumulation of reactive oxygen species. Furthermore, altered leaf morphology and chloroplast ultrastructure were observed in ATC mutants. Although less affected, DHODH knock-down mutants showed impaired seed germination and altered mitochondrial ultrastructure. Thus, DHODH might not only be regulated by respiration but also exert a regulatory function on this process. Transcriptome analysis of an ATC-amiRNA line revealed massive alterations in gene expression with central metabolic pathways being downregulated and stress response and RNA-related pathways being upregulated. In addition, genes involved in central carbon metabolism, intracellular transport and respiration were markedly downregulated in ATC mutants, being most likely responsible for the observed impaired growth. We conclude that impairment of the first committed step in pyrimidine metabolism, catalyzed by ATC, leads to nucleotide limitation and by this has far-reaching consequences on metabolism and gene expression. DHODH might closely interact with mitochondrial respiration, as seen in delayed germination, which is the reason for its localization in this organelle. [ABSTRACT FROM AUTHOR]

Water stored in trunk sapwood is vital for the canopy to maintain its physiological function under high transpiration demands. Little is known regarding the anatomical properties that contribute to the hydraulic capacitance of tree trunks and whether trunk capacitance is correlated with the hydraulic and gas exchange traits of canopy branches. We examined sapwood capacitance, xylem anatomical characteristics of tree trunks, embolism resistance, the minimal xylem water potential of canopy branches, leaf photosynthesis and stomatal conductance in 22 species from a tropical seasonal rainforest and savanna. The results showed that the mean trunk sapwood capacitance did not differ between the two biomes. Capacitance was closely related to the fiber lumen fraction and fiber wall reinforcement and not to the axial and ray parenchyma fractions. Additionally, it was positively correlated with the theoretical hydraulic conductivity of a trunk and the specific hydraulic conductivity of branches, and showed a trade-off with branch embolism resistance. Species with a high trunk sapwood capacitance maintained less negative canopy water potentials in the dry season, but higher leaf photosynthetic rates and stomatal conductance in the wet season. This study provides a functional link among trunk sapwood capacitance, xylem anatomy, canopy hydraulics and photosynthesis in tropical trees. [ABSTRACT FROM AUTHOR]

This article examines the efficiency and diversity of photorespiration, a metabolic pathway in plants that has traditionally been seen as wasteful. The authors focus on the Brassicaceae family, which includes important crop species, and investigate the presence of C3-C4 intermediates, plants that use a photorespiratory shuttle to concentrate carbon. They find that C3-C4 intermediacy is rare but present in some members of the Brassicaceae family, and they analyze the metabolic variation within this family compared to their closest C4 relative. The study provides insights into the evolution and optimization of photosynthetic pathways in different plant species. Additionally, the article discusses the potential of C3-C4 intermediates to enhance climate resilience in the face of climate change. The authors conducted a study on 28 species of Brassicaceae, a plant family without C4 relatives, and discovered significant diversity in their photosynthetic characteristics. They found that C3-C4 intermediates can efficiently reclaim CO2 and improve water use efficiency in low CO2 conditions, making them more adaptable to climate variability and abiotic stress compared to other photosynthetic types. The authors propose that these findings could be utilized to ensure food production and enhance agricultural sustainability in the future. [Extracted from the article]

Green leaf volatiles (GLVs), volatile organic compounds released by plants upon tissue damage, are key signaling molecules in plant immunity. The ability of exogenous GLV application to trigger an induced resistance (IR) phenotype against arthropod pests has been widely reported, but its effectiveness against plant pathogens is less well understood. In this study, we combined mRNA sequencing-based transcriptomics and phytohormone measurements with multispectral imaging-based precision phenotyping to gain insights into the molecular basis of Z -3-hexenyl acetate-induced resistance (Z-3-HAC-IR) in rice. Furthermore, we evaluated the efficacy of Z -3-HAC-IR against a panel of economically significant rice pathogens: Pyricularia oryzae , Rhizoctonia solani , Xanthomonas oryzae pv. oryzae , Cochliobolus miyabeanus , and Meloidogyne graminicola. Our data revealed rapid induction of jasmonate metabolism and systemic induction of plant immune responses upon Z -3-HAC exposure, as well as a transient allocation cost due to accelerated chlorophyll degradation and nutrient remobilization. Z -3-HAC-IR proved effective against all tested pathogens except for C. miyabeanus , including against the (hemi)biotrophs M. graminicola, X. oryzae pv. oryzae , and P. oryzae. The Z -3-HAC-IR phenotype was lost in the jasmonate (JA)-deficient hebiba mutant, which confirms the causal role of JA in Z -3-HAC-IR. Together, our results show that GLV exposure in rice induces broad-spectrum, JA-mediated disease resistance with limited allocation costs, and may thus be a promising alternative crop protection approach. [ABSTRACT FROM AUTHOR]

Photosynthesis is increasingly becoming a recognized target for crop improvement. Phenotyping photosynthesis-related traits on field-grown material is a key bottleneck to progress here due to logistical barriers and short measurement days. Many studies attempt to overcome these challenges by phenotyping excised leaf material in the laboratory. To date there are no demonstrated examples of the representative nature of photosynthesis measurements performed on excised leaves relative to attached leaves in crops. Here, we tested whether standardized leaf excision on the day prior to phenotyping affected a range of common photosynthesis-related traits across crop functional types using tomato (C3 dicot), barley (C3 monocot), and maize (C4 monocot). Potentially constraining aspects of leaf physiology that could be predicted to impair photosynthesis in excised leaves, namely leaf water potential and abscisic acid accumulation, were not different between attached and excised leaves. We also observed non-significant differences in spectral reflectance and chlorophyll fluorescence traits between the treatments across the three species. However, we did observe some significant differences between traits associated with gas exchange and photosynthetic capacity across all three species. This study represents a useful reference for those who perform measurements of this nature and the differences reported should be considered in associated experimental design and statistical analyses. [ABSTRACT FROM AUTHOR]

Carbon-concentrating mechanisms enhance the carboxylase efficiency of Rubisco by providing supra-atmospheric concentrations of CO2 in its surroundings. Beside the C4 photosynthesis pathway, carbon concentration can also be achieved by the photorespiratory glycine shuttle which requires fewer and less complex modifications. Plants displaying CO2 compensation points between 10 ppm and 40 ppm are often considered to utilize such a photorespiratory shuttle and are termed 'C3–C4 intermediates'. In the present study, we perform a physiological, biochemical, and anatomical survey of a large number of Brassicaceae species to better understand the C3–C4 intermediate phenotype, including its basic components and its plasticity. Our phylogenetic analysis suggested that C3–C4 metabolism evolved up to five times independently in the Brassicaceae. The efficiency of the pathway showed considerable variation. Centripetal accumulation of organelles in the bundle sheath was consistently observed in all C3–C4-classified taxa, indicating a crucial role for anatomical features in CO2-concentrating pathways. Leaf metabolite patterns were strongly influenced by the individual species, but accumulation of photorespiratory shuttle metabolites glycine and serine was generally observed. Analysis of phospho enol pyruvate carboxylase activities suggested that C4-like shuttles have not evolved in the investigated Brassicaceae. Convergent evolution of the photorespiratory shuttle indicates that it represents a distinct photosynthesis type that is beneficial in some environments. [ABSTRACT FROM AUTHOR]

The β-cyclocitric acid (β-CCA) is a bioactive apocarotenoid previously shown to improve drought tolerance in annual plants. However, the underlying molecular mechanism of this process remains largely elusive. Moreover, the question about the activity of β-CCA in perennial fruit crops is still open. Here, we found that treatment of β-CCA enhances drought tolerance in peach seedlings. The application of β-CCA significantly increased the relative water content and root activity and reduced the electrolyte leakage of peach seedlings under drought stress. Moreover, treatment with β-CCA under drought stress increased chlorophyll fluorescence, indicating a positive effect on photosynthesis, while also enhancing superoxide dismutase and peroxidase activity and reducing reactive oxygen species (ROS) levels. Consistent with these alterations, transcriptome analysis revealed an up-regulation of photosynthesis and antioxidant-related genes upon the application of β-CCA under drought stress. We also detected an induction in genes related to detoxification, environmental adaptation, primary metabolism, phytohormone, phenylpropanoid and the biosynthesis of cutin, suberine and wax, which might contribute to the induction of drought resistance. Altogether, our study reveals that β-CCA positively modulates peach drought tolerance, which is mainly mediated by enhancing photosynthesis and reducing ROS, indicating the potential of utilizing β-CCA for drought control in peach and perhaps other fruit crops. [ABSTRACT FROM AUTHOR]

Background and Aims Plasticity of leaf growth and photosynthesis is an important strategy of plants to adapt to shading stress; however, their strategy of leaf development to achieve a simultaneous increase in leaf area and photosynthesis under shading remains unknown. Methods In the present study, a pot experiment was conducted using three rapeseed genotypes of Huayouza 50 (HYZ50), Zhongshuang 11 (ZS11) and Huayouza 62 (HYZ62), and the responses of plant growth, leaf morphoanatomical traits, cell wall composition and photosynthesis to shading were investigated. Key Results Shading significantly increased leaf area per plant (LA plant) in all genotypes, but the increase in HYZ62 was greater than that in HYZ50 and ZS11. The greater increment of LA plant in HYZ62 was related to the larger decrease in leaf mass per area (LMA) and leaf density (LD), which were in turn related to less densely packed mesophyll cells and thinner cell walls (T cw). Moreover, shading significantly increased photosynthesis in HYZ62 but significantly decreased it in HYZ50. The enhanced photosynthesis in HYZ62 was related to increased mesophyll conductance (g m) due primarily to thinner cell walls. Conclusions The data presented indicate that the different plasticity of mesophyll cell density, cell wall thickness and cell wall composition in response to shading can dramatically affect leaf growth and photosynthesis. [ABSTRACT FROM AUTHOR]

Photosynthetic energy conversion for high-energy chemicals generation is one of the most viable solutions in the quest for sustainable energy towards carbon neutrality. Microalgae are fascinating photosynthetic organisms, which can directly convert solar energy into chemical energy and electrical energy. However, microalgal photosynthetic energy has not yet been applied on a large scale due to the limitation of their own characteristics. Researchers have been inspired to couple microalgae with synthetic materials via biomimetic assembly and the resulting microalgae–material hybrids have become more robust and even perform new functions. In the past decade, great progress has been made in microalgae–material hybrids, such as photosynthetic carbon dioxide fixation, photosynthetic hydrogen production, photoelectrochemical energy conversion and even biochemical energy conversion for biomedical therapy. The microalgae–material hybrid offers opportunities to promote artificially enhanced photosynthesis research and synchronously inspires investigation of biotic–abiotic interface manipulation. This review summarizes current construction methods of microalgae–material hybrids and highlights their implication in energy and health. Moreover, we discuss the current problems and future challenges for microalgae–material hybrids and the outlook for their development and applications. This review will provide inspiration for the rational design of the microalgae-based semi-natural biohybrid and further promote the disciplinary fusion of material science and biological science. [ABSTRACT FROM AUTHOR]

In plastids, conversion of light energy into ATP relies on cytochrome f, a key electron carrier with a heme covalently attached to a CXXCH motif. Covalent heme attachment requires reduction of the disulfide-bonded CXXCH by CCS5 and CCS4. CCS5 receives electrons from the oxidoreductase CCDA, while CCS4 is a protein of unknown function. In Chlamydomonas reinhardtii, loss of CCS4 or CCS5 yields a partial cytochrome f assembly defect. Here, we report that the ccs4ccs5 double mutant displays a synthetic photosynthetic defect characterized by a complete loss of holocytochrome f assembly. This defect is chemically corrected by reducing agents, confirming the placement of CCS4 and CCS5 in a reducing pathway. CCS4-like proteins occur in the green lineage, and we show that HCF153, a distant ortholog from Arabidopsis thaliana, can substitute for Chlamydomonas CCS4. Dominant suppressor mutations mapping to the CCS4 gene were identified in photosynthetic revertants of the ccs4ccs5 mutants. The suppressor mutations yield changes in the stroma-facing domain of CCS4 that restore holocytochrome f assembly above the residual levels detected in ccs5. Because the CCDA protein accumulation is decreased specifically in the ccs4 mutant, we hypothesize the suppressor mutations enhance the supply of reducing power through CCDA in the absence of CCS5. We discuss the operation of a CCS5-dependent and a CCS5-independent pathway controlling the redox status of the heme-binding cysteines of apocytochrome f. Reduction of a disulfide formed between the heme-linking cysteines of apoforms of c-type cytochromes in the thylakoid lumen requires the provision of reducing power from stroma to apocytochrome c via thiol-disulfide exchange. Reducing power is supplied through two different pathways, pathways 1 and 2, with CCDA and CCS4 being common components to both pathways. In pathway 1, CCS5 directly reduces the disulfide-bonded heme-binding site. In pathway 2, one or several yet-to-be identified protein(s) (X) reduce(s) the disulfide. CCS4 functions in stabilizing CCDA. In the absence of CCS5, gain-offunction mutations altering the C terminus of CCS4 enhance the delivery of reducing power via CCDA to the unknown reductase(s) (X), underscoring the functional importance of the soluble domain in CCS4 (indicated by a yellow star). This domain might act by recruiting the stromal reductant to CCDA or control the reactivity of the redox-active cysteines in CCDA by providing an ideal chemical microenvironment for efficient thiol-disulfide exchange. [ABSTRACT FROM AUTHOR]

Background and Aims CAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis. Results Where CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (<450 ppm) values. In turn, 21 of 25 clades containing CAM species (but where CAM origins are less certain) also arose in the past 30 million years. In these clades, CAM is probably younger than the clade origin. We found evidence for repeated weak CAM evolution during the higher CO2 conditions before 30 million years ago, and possible strong CAM origins in the Crassulaceae during the Cretaceous period prior to atmospheric CO2 decline. Most CAM-specific clades arose in the past 15 million years, in a similar pattern observed for origins of C4 clades. Conclusions The evidence indicates strong CAM repeatedly evolved in reduced CO2 conditions of the past 30 million years. Weaker CAM can pre-date low CO2 and, in the Crassulaceae, strong CAM may also have arisen in water-limited microsites under relatively high CO2. Experimental evidence from extant CAM species demonstrates that elevated CO2 reduces the importance of nocturnal CO2 fixation by increasing the contribution of C3 photosynthesis to daily carbon gain. Thus, the advantage of strong CAM would be reduced in high CO2, such that its evolution appears less likely and restricted to more extreme environments than possible in low CO2. [ABSTRACT FROM AUTHOR]

Background and Aims Bulnesia retama is a drought-deciduous, xerophytic shrub from arid landscapes of South America. In a survey of carbon isotope ratios (δ13C) in specimens from the field, B. retama exhibited less negative values, indicative of CAM or C4 photosynthesis. Here, we investigate whether B. retama is a C4 or CAM plant. Methods Gas-exchange responses to intercellular CO2, diurnal gas-exchange profiles, δ13C and dawn vs. afternoon titratable acidity were measured on leaves and stems of watered and droughted B. retama plants. Leaf and stem cross-sections were imaged to determine whether the tissues exhibited succulent CAM or C4 Kranz anatomy. Key Results Field-collected stems and fruits of B. retama exhibited δ13C between −16 and −19 ‰. Plants grown in a glasshouse from field-collected seeds had leaf δ13C values near −31 ‰ and stem δ13C values near −28 ‰. The CO2 response of photosynthesis showed that leaves and stems used C3 photosynthesis during the day, while curvature in the nocturnal response of net CO2 assimilation rate (A) in all stems, coupled with slightly positive rates of A at night, indicated modest CAM function. C4 photosynthesis was absent. Succulence was absent in all tissues, although stems exhibited tight packing of the cortical chlorenchyma in a CAM-like manner. Tissue titratable acidity increased at night in droughted stems. Conclusions Bulnesia retama is a weak to modest C3 + CAM plant. This is the first report of CAM in the Zygophyllaceae and the first showing that non-succulent, xerophytic shrubs use CAM. CAM alone in B. retama was too limited to explain less negative δ13C in field-collected plants, but combined with effects of low stomatal and mesophyll conductance it could raise δ13C to observed values between −16 and −19 ‰. Modest CAM activity, particularly during severe drought, could enable B. retama to persist in arid habitats of South America. [ABSTRACT FROM AUTHOR]

Background and Aims The relative contributions of C3 photosynthesis and crassulacean acid metabolism (CAM) during the earliest stages of development were investigated to assess how much each might contribute to cactus pear (Opuntia ficus-indica) productivity. Methods The developmental progression of C3 photosynthesis and CAM was assessed in seedlings and daughter cladodes of mature plants by titratable acidity, δ13C isotopic values and diel gas exchange measurements. Key Results Nocturnal acidification was observed in seedling cladodes and cotyledons at the earliest stages of development and became highly significant by 75 days of development. Seedling cotyledons showed mean δ13C values of −21.4 and −17.1 ‰ at 30 and 100 days of age, respectively. Seedling cladodes showed mean δ13C values of −19.4 and −14.5 ‰ at 30 and 100 days of age, respectively. These values are typical of CAM plants. Net CO2 assimilation was negative, then occurred in both the day and the night, with nighttime fixation becoming predominant once the primary cladode reached 5 cm in size. Emergent daughter cladodes growing on mature plants showed nocturnal titratable acidity at the earliest stages of development, which became significant when daughter cladodes were >2.5–5 cm in height. Emergent daughter cladodes showed mean δ13C values of −14.5 to −15.6 ‰, typical of CAM plants. CO2 assimilation studies revealed that net CO2 uptake was negative in daughter cladodes <12 cm in length, but then exhibited net positive CO2 assimilation in both the day and the night, with net nocturnal CO2 assimilation predominating once the daughter cladode grew larger. Conclusions Developing O. ficus-indica primary and daughter cladodes begin as respiring sink tissues that transition directly to performing CAM once net positive CO2 fixation is observed. Overall, these results demonstrate that CAM is the primary form of photosynthetic carbon assimilation for O. ficus-indica even at the earliest stages of seedling or daughter cladode development. [ABSTRACT FROM AUTHOR]

Crassulacean acid metabolism – or CAM photosynthesis – was described in the early to mid-20th century, and our understanding of this metabolic pathway was later expanded upon through detailed biochemical analyses of carbon balance. Soon after, scientists began to study the ecophysiological implications of CAM, and a large part of this early work was conducted in the genus Agave , in the subfamily Agavoideae of the family Asparagaceae. Today, the Agavoideae continues to be important for the study of CAM photosynthesis, from the ecophysiology of CAM species, to the evolution of the CAM phenotype and to the genomics underlying CAM traits. Here we review past and current work on CAM in the Agavoideae, in particular highlighting the work of Park Nobel in Agave , and focusing on the powerful comparative system the Agavoideae has become for studying the origins of CAM. We also highlight new genomics research and the potential for studying intraspecific variation within species of the Agavoideae, particularly species in the genus Yucca. The Agavoideae has served as an important model clade for CAM research for decades, and undoubtedly will continue to help push our understanding of CAM biology and evolution in the future. [ABSTRACT FROM AUTHOR]

Background and aims The introduction of crassulacean acid metabolism (CAM) into C3 crops has been considered as a means of improving water-use efficiency. In this study, we investigated photosynthetic and leaf structural traits in F 1 hybrids between Cymbidium ensifolium (female C3 parent) and C. bicolor subsp. pubescens (male CAM parent) of the Orchidaceae. Methods Seven F 1 hybrids produced through artificial pollination and in vitro culture were grown in a greenhouse with the parent plants. Structural, biochemical and physiological traits involved in CAM in their leaves were investigated. Key results Cymbidium ensifolium accumulated very low levels of malate without diel fluctuation, whereas C. bicolor subsp. pubescens showed nocturnal accumulation and diurnal consumption of malate. The F 1s also accumulated malate at night, but much less than C. bicolor subsp. pubescens. This feature was consistent with low nocturnal fixation of atmospheric CO2 in the F 1s. The δ13C values of the F 1s were intermediate between those of the parents. Leaf thickness was thicker in C. bicolor subsp. pubescens than in C. ensifolium , and those of the F 1s were more similar to that of C. ensifolium. This was due to the difference in mesophyll cell size. The chloroplast coverage of mesophyll cell perimeter adjacent to intercellular air spaces of C. bicolor subsp. pubescens was lower than that of C. ensifolium , and that of the F 1s was intermediate between them. Interestingly, one F 1 had structural and physiological traits more similar to those of C. bicolor subsp. pubescens than the other F 1s. Nevertheless, all F 1s contained intermediate levels of phosphoenolpyruvate carboxylase but as much pyruvate, Pi dikinase as C. bicolor subsp. pubescens. Conclusions CAM traits were intricately inherited in the F 1 hybrids, the level of CAM expression varied widely among F 1 plants, and the CAM traits examined were not necessarily co-ordinately transmitted to the F 1s. [ABSTRACT FROM AUTHOR]

Rising temperatures and extreme heat events threaten rice production. Half of the global population relies on rice for basic nutrition, and therefore developing heat-tolerant rice is essential. During vegetative development, reduced photosynthetic rates can limit growth and the capacity to store soluble carbohydrates. The photosystem II (PSII) complex is a particularly heat-labile component of photosynthesis. We have developed a high-throughput chlorophyll fluorescence-based screen for photosynthetic heat tolerance capable of screening hundreds of plants daily. Through measuring the response of maximum PSII efficiency to increasing temperature, this platform generates data for modelling the PSII–temperature relationship in large populations in a small amount of time. Coefficients from these models (photosynthetic heat tolerance traits) demonstrated high heritabilities across African (Oryza glaberrima) and Asian (Oryza sativa , Bengal Assam Aus Panel) rice diversity sets, highlighting valuable genetic variation accessible for breeding. Genome-wide association studies were performed across both species for these traits, representing the first documented attempt to characterize the genetic basis of photosynthetic heat tolerance in any species to date. A total of 133 candidate genes were highlighted. These were significantly enriched with genes whose predicted roles suggested influence on PSII activity and the response to stress. We discuss the most promising candidates for improving photosynthetic heat tolerance in rice. [ABSTRACT FROM AUTHOR]