Regulation Of Photosynthesis Research Articles

Characterization of Low-Temperature Sensitivity and Chlorophyll Fluorescence in Yellow Leaf Mutants of Tomato

Leaf color mutants serve as valuable models for studying the regulation of plant photosynthesis, alternations in chloroplast structure and function, and the analysis of associated gene functions. A yellow leaf mutant, ylm, was separated from the wild tomato M82, with its yellowing intensity influenced by low temperature. To assess the low-temperature sensitivity of this mutant, the photosynthetic and chlorophyll fluorescence responses of ylm and M82 were examined under different temperature conditions. In this study, the ylm mutant and its wild type, M82, were exposed to three temperature levels, 16, 25, and 30 °C, for 48 h. The impact of these temperature treatments on leaf color change, chlorophyll content, photosynthetic performance, and chlorophyll fluorescence characteristics of mutant ylm was investigated. The results revealed the following: (1) After exposure to 16 °C, the ylm mutant exhibited significant yellowing, a marked reduction in chlorophyll content, and a notable increase in carotenoid content. At 25 °C, the differences were less pronounced, and at 30 °C, the differences between ylm and M82 were minimal. (2) The photosynthetic rate of the ylm mutant was lower than that of M82 at 16 °C, with the gap narrowing as temperature increased, eventually converging at higher temperatures. (3) The fluorescence transient curve (OJIP) of the ylm mutant differed significantly from that of M82 at 16 °C, with higher fluorescence intensity at the O point and lower intensity at the J, I, and P points. This difference was decreased at 25 °C and nearly disappeared at 30 °C. Additionally, the Fv/Fm, Fv/Fo, PIabs, PItotal, ABS/CSm, TRo/CSm, and ETo/CSm values of ylm were lower than those of M82 at 16 °C, while the ABS/RC and DIo/RC values were higher, with no significant differences observed at 30 °C. These findings suggest that the ylm mutant is highly sensitive to low temperature, with pronounced yellowing, reduced light energy absorption and capture efficiency, and impaired electron transport at lower temperature.

The transcription factor RppA regulates chlorophyll and carotenoid biosynthesis to improve photoprotection in cyanobacteria.

Chlorophyll is an essential photosynthetic pigment but also a strong photosensitizer. Excessive free chlorophyll and its precursors can cause oxidative damage to photosynthetic organisms. Cyanobacteria are the oldest oxygenic photosynthetic organisms and the ancestors of the chloroplast. Owing to their complex habitats, cyanobacteria require precise regulation of chlorophyll synthesis to respond to environmental factors, especially changes in light. Chlorophyll synthase, encoded by chlG, is the enzyme catalyzing the final step of chlorophyll biosynthesis, which is closely related to photosynthesis biogenesis. However, the transcriptional regulation on chlG remains unclear. Here, the transcription factor, regulator of photosynthesis and photopigment-related gene expression A (RppA) was identified to bind to the chlG promoter by screening a yeast one-hybrid library in the cyanobacterium Synechocystis sp. PCC 6803. The rppA knock-out mutant showed a phenotype of slow growth and severe oxidative damage under dark-light transition conditions. The up-regulated transcriptional expression of chlG was significantly higher and more chlorophyll and its precursors accumulated in the rppA knock-out mutant than those in the wild-type strain during the transition from darkness to light, indicating RppA represses the expression of chlG in Synechocystis. Meanwhile, RppA could synchronously promote the transcription of carotenoids biosynthesis-related genes to enhance carotenoids synthesis during the dark-light transition. These results reveal synergistic regulation of chlorophyll and carotenoids biosynthesis in cyanobacteria in response to frequent dark-light transitions, which slows down chlorophyll biosynthesis while promoting carotenoids biosynthesis to avoid oxidative damage caused by excessive reactive oxygen species accumulation.

Comparative Analysis of Phytohormone Biosynthesis Genes Responses to Long-Term High Light in Tolerant and Sensitive Wheat Cultivars.

Phytohormones are vital for developmental processes, from organ initiation to senescence, and are key regulators of growth, development, and photosynthesis. In natural environments, plants often experience high light (HL) intensities coupled with elevated temperatures, which pose significant threats to agricultural production. However, the response of phytohormone-related genes to long-term HL exposure remains unclear. Here, we examined the expression levels of genes involved in the biosynthesis of ten phytohormones, including gibberellins, cytokinins, salicylic acid, jasmonic acid, abscisic acid, brassinosteroids, indole-3-acetic acid, strigolactones, nitric oxide, and ethylene, in two winter wheat cultivars, Xiaoyan 54 (XY54, HL tolerant) and Jing 411 (J411, HL sensitive), when transferred from low light to HL for 2-8 days. Under HL, most genes were markedly inhibited, while a few, such as TaGA2ox, TaAAO3, TaLOG1, and TaPAL2, were induced in both varieties. Interestingly, TaGA2ox2 and TaAAO3 expression positively correlated with sugar content but negatively with chlorophyll content and TaAGP expression. In addition, we observed that both varieties experienced a sharp decline in chlorophyll content and photosynthesis performance after prolonged HL exposure, with J411 showing significantly more sensitivity than XY54. Hierarchical clustering analysis classified the phytohormone genes into the following three groups: Group 1 included six genes highly expressed in J411; Group 2 contained 25 genes drastically suppressed by HL in both varieties; and Group 3 contained three genes highly expressed in XY54. Notably, abscisic acid (ABA), and jasmonic acid (JA) biosynthesis genes and their content were significantly higher, while gibberellins (GA) content was lower in XY54 than J411. Together, these results suggest that the differential expression and content of GA, ABA, and JA play crucial roles in the contrasting responses of tolerant and sensitive wheat cultivars to leaf senescence induced by long-term HL. This study enhances our understanding of the mechanisms underlying HL tolerance in wheat and can guide the development of more resilient wheat varieties.

Triacontanol Reverses Abscisic Acid Effects on Stomatal Regulation in Solanum lycopersicum L. under Drought Stress Conditions

When applied under abiotic stress conditions, triacontanol (TRIA) is effective in regulating the physicochemical processes in plants through mechanisms of defence such as abscisic acid (ABA) signalling. However, TRIA’s role in relation to ABA and stomatal opening is unclear. Therefore, the objective of this study was to evaluate the effects of TRIA and ABA and their combinations on different variables related to stomatal regulation in Solanum lycopersicum, which is subjected to drought stress, and on the leaf epidermis. The negative effects of stress and responses triggered by ABA were reversed in plants treated with TRIA. TRIA increased stomatal conductance and photosynthetic activity in the early hours, and it was determined that TRIA produced larger stomata than did the other treatments. Moreover, the chloroplasts of plants treated with TRIA were significantly smaller and more numerous than those of the control, which could improve CO2 diffusion efficiency and may be related to the regulation of stomatal opening and photosynthesis. Finally, the abaxial epidermis tests reaffirmed the inhibitory effects of TRIA on ABA on stomatal opening. These results confirm the important role of TRIA in regulating various processes in plants and processes triggered by ABA, such as those related to stomatal regulation.

Participation of the stress-responsive CDSP32 thioredoxin in the modulation of chloroplast ATP-synthase activity in Solanum tuberosum.

Plant thioredoxins (TRXs) are involved in numerous metabolic and signalling pathways, such as light-dependent regulation of photosynthesis. The atypical TRX CDSP32, chloroplastic drought-induced stress protein of 32 kDa, includes two TRX-fold domains and participates in responses to oxidative stress as an electron donor to other thiol reductases. Here, we further characterised potato lines modified for CDSP32 expression to clarify the physiological roles of the TRX. Upon high salt treatments, modified lines displayed changes in the abundance and redox status of CDSP32 antioxidant partners, and exhibited sensitivity to combined saline-alkaline stress. In non-stressed plants overexpressing CDSP32, a lower abundance of photosystem II subunits and ATP-synthase γ subunit was noticed. The CDSP32 co-suppressed line showed altered chlorophyll a fluorescence induction and impaired regulation of the transthylakoid membrane potential during dark/light and light/dark transitions. These data, in agreement with the previously reported interaction between CDSP32 and ATP-synthase γ subunit, suggest that CDSP32 affects the redox regulation of ATP-synthase activity. Consistently, modelling of protein complex 3-D structure indicates that CDSP32 could constitute a suitable partner of ATP-synthase γ subunit. We discuss the roles of the TRX in the regulation of both photosynthetic activity and enzymatic antioxidant network in relation with environmental conditions.

Caught between two states: The compromise in acclimation of photosynthesis, transpiration and mesophyll conductance to different amplitudes of fluctuating irradiance.

While dynamic regulation of photosynthesis in fluctuating light is increasingly recognized as an important driver of carbon uptake, acclimation to realistic irradiance fluctuations is still largely unexplored. We subjected Arabidopsis thaliana (L.) wild-type and jac1 mutants to irradiance fluctuations with distinct amplitudes and average irradiance. We examined how irradiance fluctuations affected leaf structure, pigments and physiology. A wider amplitude of fluctuations produced a stronger acclimation response. Large reductions of leaf mass per area under fluctuating irradiance framed our interpretation of changes in photosynthetic capacity and mesophyll conductance as measured by three separate methods, in that photosynthetic investment increased markedly on a mass basis, but only a little on an area basis. Moreover, thermal imagery showed that leaf transpiration was four times higher under fluctuating irradiance. Leaves growing under fluctuating irradiance, although thinner, maintained their photosynthetic capacity, as measured through light- and CO2-response curves; suggesting their photosynthesis may be more cost-efficient than those under steady light, but overall may incur increased maintenance costs. This is especially relevant for plant performance globally because naturally fluctuating irradiance creates conflicting acclimation cues for photosynthesis and transpiration that may hinder progress towards ensuring food security under climate-related extremes of water stress.

Interference of skeleton photoperiod in circadian clock and photosynthetic efficiency of tea plant: in-depth analysis of mathematical model.

The circadian system of plants is a complex physiological mechanism, a biological process in which plants can adjust themselves according to the day and night cycle. To understand the effects of different photoperiods on the biological clock of tea plants, we analyzed the expression levels of core clock genes (CCA1, PRR9, TOC1, ELF4) and photosynthesis-related genes (Lhcb, RbcS, atpA) under normal light (light/dark = 12h/12h, 12L12D) and took the cost function defined by cycle and phase errors as the basic model parameter. In the continuous light environment (24h light, 24L), the peak activity and cycle of key genes that control the biological clock and photosynthesis were delayed by 1-2h. Under a skeleton photoperiod (6L6D, 3L3D), the expression profiles of clock genes and photosynthesis-related genes in tea plants were changed and stomatal opening showed a circadian rhythm. These observations suggest that a skeleton photoperiod may have an effect on the circadian rhythm, photosynthetic efficiency and stomatal regulation of tea plants. Our study and model analyzed the components of circadian rhythms under different photoperiodic pathways, and also revealed the underlying mechanisms of circadian regulation of photosynthesis in tea plants.

The yellow-cotyledon gene (ATYCO) is a crucial factor for thylakoid formation and photosynthesis regulation in Arabidopsis

Chloroplast development underpins plant growth, by facilitating not only photosynthesis but also other essential biochemical processes. Nonetheless, the regulatory mechanisms and functional components of chloroplast development remain largely uncharacterized due to their complexity. In our study, we identified a plastid-targeted gene, ATYCO/RP8/CDB1, as a critical factor in early chloroplast development in Arabidopsis thaliana. YCO knock-out mutant (yco) exhibited a seedling-lethal, albino phenotype, resulting from dysfunctional chloroplasts lacking thylakoid membranes. Conversely, YCO knock-down mutants produced a chlorophyll-deficient cotyledon and normal leaves when supplemented with sucrose. Transcription analysis also revealed that YCO deficiency could be partially compensated by sucrose supplementation, and that YCO played different roles in the cotyledons and the true leaves. In YCO knock-down mutants, the transcript levels of plastid-encoded RNA polymerase (PEP)-dependent genes and nuclear-encoded photosynthetic genes, as well as the accumulation of photosynthetic proteins, were significantly reduced in the cotyledons. Moreover, the chlorophyll-deficient phenotype in YCO knock-down line can be effectively suppressed by inhibition of PSI cyclic electron transport activity, implying an interaction between YCO and PSI cyclic electron transport. Taken together, our findings de underscore the vital role of YCO in early chloroplast development and photosynthesis.

Integrated metabolome and transcriptome analysis revealed color formation in purple leaf mustard (Brassica juncea)

Purple leaf mustard has garnered attention owing to its abundant anthocyanin content. This study investigated the phenolic metabolome and transcriptome of purple variety ZC-Red and green variety ZC-2. Each of the two varieties had three biological replicates, and each replicate consisted of ten leaves from five plants. Phenolic metabolome was analyzed using an ultra-high performance liquid chromatography system and tandem mass spectrometry, and the transcriptome sequencing platform was the Illumina NovaSeq 6000 platform. The green variety ZC-2 was used as the control for differential analysis. All differential metabolites and genes were significant. Findings revealed the accumulation of anthocyanins in ZC-Red, whereas ZC-2 exhibited higher levels of phenolic acids and flavonoids, excluding anthocyanins. This could be attributed to the directional preference of the phenylpropanoid metabolic flow. Transcriptome analysis highlighted the pivotal roles of phenylpropanoid metabolism and photosynthesis in color formation. In ZC-Red, nearly all anthocyanin biosynthesis genes exhibited up-regulation, with multiple genes in late biosynthesis showing increases thousands of times greater than ZC-2. Conversely, the expression of genes associated with photosystem subunits and light-harvesting complexes was down-regulated. Key candidate transcription factors, including MYB113, TT8, WRKY44, and MYB30, were identified as regulators of anthocyanin and photosynthesis. Findings contribute valuable insights into the molecular mechanisms underlying anthocyanin accumulation. Core differential metabolites such as anthocyanins and phenolic acids are of great significance to the utilization of diversified functional compounds and targeted breeding of leaf mustard.

Proteomic analysis of unicellular cyanobacterium Crocosphaera subtropica ATCC 51142 under extended light or dark growth.

The daily light-dark cycle is a recurrent and predictable environmental phenomenon to which many organisms, including cyanobacteria, have evolved to adapt. Understanding how cyanobacteria alter their metabolic attributes in response to subjective light or dark growth may provide key features for developing strains with improved photosynthetic efficiency and applications in enhanced carbon sequestration and renewable energy. Here, we undertook a label-free proteomic approach to investigate the effect of extended light (LL) or extended dark (DD) conditions on the unicellular cyanobacterium Crocosphaera subtropica ATCC 51142. We quantified 2287 proteins, of which 603 proteins were significantly different between the two growth conditions. These proteins represent several biological processes, including photosynthetic electron transport, carbon fixation, stress responses, translation, and protein degradation. One significant observation is the regulation of over two dozen proteases, including ATP dependent Clp-proteases (endopeptidases) and metalloproteases, the majority of which were upregulated in LL compared to DD. This suggests that proteases play a crucial role in the regulation and maintenance of photosynthesis, especially the PSI and PSII components. The higher protease activity in LL indicates a need for more frequent degradation and repair of certain photosynthetic components, highlighting the dynamic nature of protein turnover and quality control mechanisms in response to prolonged light exposure. The results enhance our understanding of how Crocosphaera subtropica ATCC51142 adjusts its molecular machinery in response to extended light or dark growth conditions.

Selecting appropriate forage cover crops to improve growth, yield, and fruit quality of wolfberry by regulation of photosynthesis and biotic stress resistance

Forage cover crops have the potential to improve soil quality and orchard productivity, but their effects on wolfberry (Lycium barbarum L.) plants are still unclear. In this study, we conducted field and greenhouse experiments between 2019 and 2021, with 10 forage species as cover crops. We observed the growth, yield, fruit quality, and photosynthetic characteristics of wolfberry plants, as well as the occurrence of plant diseases and pests. Based on averaged data for all forage species, cover cropping facilitated plant growth, maintained fruit yield, and promoted leaf photosynthesis in wolfberry compared to monocropping. This was exemplified by a notable increase in the branch number of wolfberry plants under ryegrass treatment, with marginal increase in branch length under evergreen grass (lvyuan 5) and mangold treatments. Cover cropping additionally improved wolfberry quality through increasing carotenoid, flavonoid, and ascorbic acid contents by 21%, 53%, and 127%, respectively (P< 0.05). The presence of mangold, alfalfa, sweet sorghum, ryegrass, and feather grass reduced powdery mildew-induced leaf damage in wolfberry plants by 69% (P< 0.05). When alfalfa, feather grass, and ryegrass were used, the risk of aphid infestation was lowered by 67% (P< 0.05). Collectively, the results indicated that mangold, ryegrass, and alfalfa were the optimal cover crops for sustainable wolfberry production in the study area. The use of appropriate forage cover crops enhanced plant growth and fruit quality of wolfberry by stimulating photosynthetic capacity and biotic stress resistance.

The Use of Thioxopyrimidine Derivatives as New Regulators of Growth and Photosynthesis of Barley

New synthetic compounds - thioxopyrimidine derivatives as regulators of vegetative growth and photosynthesis of spring barley (Hordeum vulgare L.) variety Acordine were studied. The growth-regulatory effect of new synthetic compounds, thioxopyrimidine derivatives, used in a concentration of 10-6M, was compared with the growth-regulatory effect of a plant hormone auxin IAA (1H-indol-3-yl)acetic acid) or synthetic plant growth regulators, derivatives of sodium and potassium salts of 6-methyl-2-mercapto-4-hydroxypyrimidine (Methyur, Kamethur), N-oxide-2,6-dimethylpyridine (Ivin), used in a similar concentration of 10-6M. The conducted study showed the similarity of the growth-regulatory effects of synthetic compounds, thioxopyrimidine derivatives, the plant hormone auxin IAA, and synthetic plant growth regulators Methyur, Kamethur, and Ivin. Morphometric parameters (average length of shoots (mm), average length of roots (mm), and average biomass of 10 plants (g)) and biochemical parameters (content of photosynthetic pigments chlorophylls a, b, a+b and carotenoids (µg/ml)) of barley plants treated with the plant hormone auxin IAA or synthetic plant growth regulators Methyur, Kamethur, Ivin or thioxopyrimidine derivatives were increased after 4 weeks compared to control plants. The dependence of the growth-regulatory effect of synthetic compounds, thioxopyrimidine derivatives on their chemical structure was analyzed. The use of the synthetic plant growth regulators, derivatives of sodium salt of 6-methyl-2-mercapto-4-hydroxypyrimidine (Methyur), potassium salt of 6-methyl-2-mercapto-4-hydroxypyrimidine (Kamethur), N-oxide-2,6-dimethylpyridine (Ivin) and selected most active synthetic compounds, thioxopyrimidine derivatives for regulating the growth and photosynthesis of spring barley (Hordeum vulgare L.) variety Acordine is proposed.

Regulation of stomatal development by epidermal, subepidermal and long-distance signals.

Plant leaves consist of three layers, including epidermis, mesophyll and vascular tissues. Their development is meticulously orchestrated. Stomata are the specified structures on the epidermis for uptake of carbon dioxide (CO2) while release of water vapour and oxygen (O2), and thus play essential roles in regulation of plant photosynthesis and water use efficiency. To function efficiently, stomatal formation must coordinate with the development of other epidermal cell types, such as pavement cell and trichome, and tissues of other layers, such as mesophyll and leaf vein. This review summarizes the regulation of stomatal development in three dimensions (3D). In the epidermis, specific stomatal transcription factors determine cell fate transitions and also activate a ligand-receptor- MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) signaling for ensuring proper stomatal density and patterning. This forms the core regulation network of stomatal development, which integrates various environmental cues and phytohormone signals to modulate stomatal production. Under the epidermis, mesophyll, endodermis of hypocotyl and inflorescence stem, and veins in grasses secrete mobile signals to influence stomatal formation in the epidermis. In addition, long-distance signals which may include phytohormones, RNAs, peptides and proteins originated from other plant organs modulate stomatal development, enabling plants to systematically adapt to the ever changing environment.

Full-length transcriptome sequencing of Arabidopsis plants provided new insights into the autophagic regulation of photosynthesis

Autophagy is a highly conserved eukaryotic pathway and plays a crucial role in cell survival under stress conditions. Here, we applied a full-length transcriptome approach to study an Arabidopsis autophagy mutant (atg5-1) subjected to nitrogen-starvation, using Oxford Nanopore Technologies. A total of 39,033 transcripts were identified, including 11,356 new transcripts. In addition, alternative splicing (AS) events and lncRNAs were also detected between Col-0 (WT) and atg5-1. Differentially expressed transcript enrichment showed that autophagy upregulates the expression of many stress-responsive genes and inhibits the transcription of photosynthesis-associated genes. The qRT-PCR results showed that the expression patterns of photosynthesis-related genes in the atg5-1 differed under the conditions of nitrogen starvation and carbon starvation. Under nitrogen starvation treatment, many genes related to photosynthesis also exhibited AS. Chlorophyll fluorescence images revealed that the Fv/Fm and ΦPSII of old atg5-1 leaves were significantly reduced after nitrogen starvation treatment, but the Y(NPQ) indices were significantly increased compared to those of the WT plants. The results of qRT-PCR suggest that autophagy appears to be involved in the degradation of genes related to photodamage repair in PSII. Taken together, the full-length transcriptiome sequencing provide new insights into how new transcripts, lncRNAs and alternative splicing (AS) are involved in plant autophagy through full-length transcriptome sequencing and suggest a new potential link between autophagy and photosynthesis.

The regulation of photosynthesis and growth of rapeseed seedling by the interaction of red and yellow lights with blue light

The interactive regulation among different lights on plant life-activities has not yet been fully understood. In the study, we investigated the interaction of red light (R) and yellow light (Y) with blue light (B) on growth and photosynthesis of rapeseed seedlings. The results showed Y and R as well as their combination of RY were not beneficial for plant photosynthesis and growth, but a quarter addition of B (RB, YB and RBY) obviously reversed these negative effects, improving stomatal behavior, leaf and root developments, photosynthetic traits, as well as synthesis and transport of photosynthetic products. Available light energy and B intervention together decreased the ratio of chlorophyll b (Chl b) to carotenoid (Car), while the opposite effect was observed in the absence of B treatments. Among the various lights, RY and Y significantly upregulated the majority of genes associated with chlorophyll metabolism, while RB predominantly upregulated genes related to the two photosystems (PS). Conversely, B and YB treatments generally suppressed the expression of these genes. Despite these differences in gene expression, the ratios of PSI/PSII to Chl b/Car were consistently maintained around 0.56 in the RB, YB, and RBY treatments. In contrast, this ratio was higher at 0.64 in the B treatment and lower, at less than 0.44, in the R, Y, and RY treatments. These ratios reflect the balance between light supply and utilization in plants under different lights, where plants under RB, YB, and RBY might achieve optimal light environments, while plants under B and under R, Y, and RY experienced high and low light stress, respectively. In conclusion, all combinations of B with R, Y or RY can be used for rapeseed cultivation, and the ratio of Chl b/Car to PSI/PSII might be an important reference index to select optimal light combinations for crop production.

Transcriptome analysis reveals the molecular mechanism of differences in growth between photoautotrophy and heterotrophy in Chlamydomonas reinhardtii.

The green alga Chlamydomonas reinhardtii can grow photoautotrophically utilizing light and CO2, and heterotrophically utilizing acetate. The physiological and biochemical responses of autotrophy and heterotrophy are different in C. reinhardtii. However, there is no complete understanding of the molecular physiology between autotrophy and heterotrophy. Therefore, we performed biochemical, molecular and transcriptome analysis of C. reinhardtii between autotrophy and heterotrophy. The cell growth characterization demonstrated that heterotrophic cell had enhanced growth rates, and autotrophic cell accumulated more chlorophyll. The transcriptome data showed that a total of 2,970 differentially expressed genes (DEGs) were identified from photoautotrophy 12h (P12h) to heterotrophy 12h (H12h). The DEGs were involved in photosynthesis, the tricarboxylic acid cycle (TCA), pyruvate and oxidative phosphorylation metabolisms. Moreover, the results of qRT-PCR revealed that the relative expression levels of malate dehydrogenase (MDH), succinate dehydrogenase (SDH), ATP synthase (ATPase), and starch synthase (SSS) were increased significantly from P12h and H12h. The protein activity of NAD-malate dehydrogenase (NAD-MDH) and succinate dehydrogenase (SDH) were significantly higher in the H12h group. The above results indicated that the high growth rate observed in heterotrophic cell may be the effects of environmental or genetic regulation of photosynthesis. Therefore, the identification of novel candidate genes in heterotrophy will contribute to the development of microalga strains with higher growth capacity and better performance for biomass production.

Nitric oxide signal is required for glutathione-induced enhancement of photosynthesis in salt-stressed Solanum lycopersicum L.

Reduced glutathione (γ-glutamyl-cysteinyl-glycine, GSH), the primary non-protein sulfhydryl group in organisms, plays a pivotal role in the plant salt stress response. This study aimed to explore the impact of GSH on the photosynthetic apparatus, and carbon assimilation in tomato plants under salt stress, and then investigate the role of nitric oxide (NO) in this process. The investigation involved foliar application of 5 mM GSH, 0.1% (w/v) hemoglobin (Hb, a nitric oxide scavenger), and GSH+Hb on the endogenous NO levels, rapid chlorophyll fluorescence, enzyme activities, and gene expression related to the Calvin cycle in tomato seedlings (Solanum lycopersicum L. cv. 'Zhongshu No. 4') subjected short-term salt stress (100 mM NaCl) for 24, 48 and 72 hours. GSH treatment notably boosted nitrate reductase (NR) and NO synthase (NOS) activities, elevating endogenous NO signaling in salt-stressed tomato seedling leaves. It also mitigated chlorophyll fluorescence (OJIP) curve distortion and damage to the oxygen-evolving complex (OEC) induced by salt stress. Furthermore, GSH improved photosystem II (PSII) electron transfer efficiency, reduced QA - accumulation, and countered salt stress effects on photosystem I (PSI) redox properties, enhancing the light energy absorption index (PIabs). Additionally, GSH enhanced key enzyme activities in the Calvin cycle and upregulated their genes. Exogenous GSH optimized PSII energy utilization via endogenous NO, safeguarded the photosynthetic reaction center, improved photochemical and energy efficiency, and boosted carbon assimilation, ultimately enhancing net photosynthetic efficiency (Pn) in salt-stressed tomato seedling leaves. Conversely, Hb hindered Pn reduction and NO signaling under salt stress and weakened the positive effects of GSH on NO levels, photosynthetic apparatus, and carbon assimilation in tomato plants. Thus, the positive regulation of photosynthesis in tomato seedlings under salt stress by GSH requires the involvement of NO.

Seasonal dynamics and punctuated carbon sink reduction suggest photosynthetic capacity of boreal silver birch is reduced by the accumulation of hexose.

The 'assimilates inhibition hypothesis' posits that accumulation of nonstructural carbohydrates (NSCs) in leaves reduces leaf net photosynthetic rate, thus internally regulating photosynthesis. Experimental work provides equivocal support mostly under controlled conditions without identifying a particular NSC as involved in the regulation. We combined 3-yr in situ leaf gas exchange observations (natural dynamics) in the upper crown of mature Betula pendula simultaneously with measurements of concentrations of sucrose, hexoses (glucose and fructose), and starch, and similar measurements during several one-day shoot girdling (perturbation dynamics). Leaf water potential and water and nitrogen content were measured to account for their possible contribution to photosynthesis regulation. Leaf photosynthetic capacity (A/Ci) was temporally negatively correlated with NSC accumulation under both natural and perturbation states. For developed leaves, leaf hexose concentration explained A/Ci variation better than environmental variables (temperature history and daylength); the opposite was observed for developing leaves. The weaker correlations between NSCs and A/Ci in developing leaves may reflect their strong internal sink strength for carbohydrates. By contrast, the strong decline in photosynthetic capacity with NSCs accumulation in mature leaves, observed most clearly with hexose, and even more tightly with its constituents, provides support for the role of assimilates in regulating photosynthesis under natural conditions.

Cyanobacterial α-carboxysome carbonic anhydrase is allosterically regulated by the Rubisco substrate RuBP.

Cyanobacterial CO2 concentrating mechanisms (CCMs) sequester a globally consequential proportion of carbon into the biosphere. Proteinaceous microcompartments, called carboxysomes, play a critical role in CCM function, housing two enzymes to enhance CO2 fixation: carbonic anhydrase (CA) and Rubisco. Despite its importance, our current understanding of the carboxysomal CAs found in α-cyanobacteria, CsoSCA, remains limited, particularly regarding the regulation of its activity. Here, we present a structural and biochemical study of CsoSCA from the cyanobacterium Cyanobium sp. PCC7001. Our results show that the Cyanobium CsoSCA is allosterically activated by the Rubisco substrate ribulose-1,5-bisphosphate and forms a hexameric trimer of dimers. Comprehensive phylogenetic and mutational analyses are consistent with this regulation appearing exclusively in cyanobacterial α-carboxysome CAs. These findings clarify the biologically relevant oligomeric state of α-carboxysomal CAs and advance our understanding of the regulation of photosynthesis in this globally dominant lineage.

Effects of electrical stimulation on carbon sequestration of photosynthetic bacteria: Response of the photosynthetic unit to electrical stimulation

Bioelectrochemical systems have been used to enhance the carbon sequestration of photosynthetic bacteria (PSB), but it is unclear whether the electrical stimulation affects the structure of membrane proteins involved in photochemical activity. In this study, the rate of CO2 fixation in the photosynthetic bacteria R. palustris increased with electrical stimulation, and the enhancement partly remained even after the power off. The CO2 fixation rate in electrical-stimulated PSB was 10% higher than in non-stimulated PSB, and the activity of the CO2 fixation enzyme Rubisco was 16% higher. This resulted from the improved light utilization efficiency of the photosynthetic units in R. palustris after electrical stimulation, particularly due to the enhancement of the primary reaction mediated by the light capture protein RC-LH1. The molar extinction coefficient of the light capture protein RC-LH1 increased from 3301 cm−1 mM−1 to 3733 cm−1 mM−1, and the maximum rate of the primary reaction increased from 6.88 × 10−3 e−RC−1s−1 to 8.66 × 10−3 e−RC−1s−1. Circular dichroism spectroscopy and Fourier transform infrared spectroscopy indicated that the electrical stimulation increased the dipole moment of the α-helix in RC-LH1 to facilitate the quinone transport in the primary reaction. Nuclear magnetic resonance spectroscopy revealed that the electrical stimulation increased the formation of hydrogen bonds in bacteriochlorophyll a for electron transition. This study investigated the response of photosynthetic bacteria to electrical stimulation, providing a distinct outlook on the electrochemical regulation of photosynthesis for carbon capture.