Search Results (257)

Photosynthetic carbon assimilation under photorespiratory conditions requires tight coordination between chloroplast electron transport and mitochondrial redox metabolism, yet the contribution of mitochondrial alternative oxidase (AOX) remains unresolved. Using 1 mM salicylhydroxamic acid (SHAM) to inhibit the AOX pathway in Rumex K-1 leaves, we investigated how mitochondrial alternative respiration contributes to carbon assimilation. AOX inhibition imposed a non-stomatal limitation on CO₂ assimilation and reduced photosystem II (PSII) electron transport. However, low O₂ or elevated CO₂ alleviated the decline in CO₂ assimilation while PSII photochemistry remained depressed, and AOX inhibition reduced apparent V_cmax without significantly affecting J_max, indicating that the primary constraint lay downstream of PSII in photorespiratory carbon metabolism. Electron flux through PSII and the electron fluxes supporting the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles all decreased under SHAM treatment, indicating reduced PSII electron transport and electron use associated with carbon assimilation and photorespiration. AOX inhibition caused glycine accumulation and increased the Gly/Ser ratio under illumination but not in darkness, indicating restricted mitochondrial glycine-to-serine conversion during photorespiration. Together, these responses suggest that AOX-dependent ubiquinol oxidation helps sustain mitochondrial NADH reoxidation and NAD⁺ regeneration, thereby supporting glycine-to-serine conversion and photorespiratory carbon recycling. Full article

Yield losses due to water-deficit (WD) conditions, especially during the reproductive stages of plant development, pose a significant threat to global canola (Brassica napus L.) production. Therefore, it is critical to investigate traits contributing to improved productivity under increased WD conditions. Here we present phenotypic, physiological and transcriptomic changes in response to WD across contrasting canola accessions exhibiting variation in drought resistance-related traits. WD significantly reduced shoot biomass, plant height, harvest index, leaf water content, photosynthetic CO₂ assimilation rate, intrinsic water-use efficiency and carbon isotope discrimination. WD caused 49 to 100% of the seed yield reduction: the minimum seed yield reduction (49.66%) was observed in a doubled-haploid (DH) line, 06-5101.137, while the maximum yield reduction (94.1 to 100%) occurred in the late-flowering DH lines (06.5101.088 and 06-5101.306). Seed yield showed a positive correlation (r = 0.29 to 0.95) with shoot biomass and harvest index, leaf water content, photosynthetic CO₂ assimilation rate, intrinsic water use efficiency and carbon isotope discrimination. However, it showed negative correlations with days to flower, leaf specific weight, root length, root biomass (r = −0.04 to −0.79) across water treatments. The specific leaf transcriptome analysis of the two parental lines of DH population that exhibit variation for effective water use under well-watered and water-deficient conditions revealed different categories of differentially expressed genes (DEGs): WD-responsive DEGs in BC1329 parental line (1116) and BC9102 (1205) with 754 and 853 DEGs unique to BC1329 and BC9102, respectively, WD-responsive DEGs (906), genotype-dependent DEGs (8465) and genotype × treatment interaction DEGs (353). DEG annotations revealed that the WD-treatment-affected genes were involved in stress responses and growth and development. We further located 235 DEGs within the QTL regions underlying agronomic and physiological performance. Our study provides a conceptual framework for the morphological, physiological and molecular determinants involved in water-use efficiency. Seedlings’ traits with high heritability values, such as shoot biomass, leaf weight, leaf water content and Δ¹³C, serve as proxies for trait-based selection for improved seed yield under both water-limited and non-water-limited conditions. Full article

Light is a key environmental factor regulating plant photosynthesis, yet the coordinated effects of photoperiod and light intensity on photosynthetic dynamics in non-heading Chinese cabbage remain unclear. Using experimental data, we developed a circadian clock-controlled photosynthesis model integrating photoperiod and light-intensity inputs. The model was calibrated and evaluated against experimental observations and was then used to analyze circadian gene expression, diurnal net photosynthetic rate ($Pn$), light-period net CO₂ assimilation, and the marginal carbon benefit of increasing daily light integral (DLI). Under a constant DLI of 9.216 mol·m⁻²·d⁻¹, extending the photoperiod from 8 to 20 h while reducing light intensity from 320 to 128 µmol·m⁻²·s⁻¹ lowered and delayed the instantaneous $Pn$ peak but progressively increased light-period net CO₂ assimilation. Among the treatments examined, 20L:4D produced the highest net CO₂ assimilation. Moreover, across the simulated DLI range of 5–19 mol·m⁻²·d⁻¹, the 20-h photoperiod consistently produced the highest net assimilation, whereas the marginal carbon benefit of additional light declined by approximately 62%. The results suggest that distributing a fixed daily light input over a longer photoperiod at lower instantaneous light intensity can enhance daily carbon gain within the tested range, whereas increasing DLI produces progressively diminishing photosynthetic returns. This study provides a modeling framework for evaluating photoperiod–light intensity coordination and provides a quantitative basis for optimizing light–environment management in controlled-environment agriculture. Full article

Rising atmospheric CO₂ is altering carbon–nitrogen interactions in C₃ crops, with tomato (Solanum lycopersicum L.) showing enhanced carbon assimilation but frequently reduced nitrogen acquisition and assimilation. Nitrate reductase (NR), the rate-limiting enzyme in nitrate reduction, plays a central role by integrating nitrate assimilation with carbon metabolism and nitric oxide (NO) signaling. This review summarizes current knowledge of NR regulation in tomato under elevated CO₂ (eCO₂), focusing on post-translational mechanisms and their contribution to photosynthetic acclimation. Elevated CO₂ modulates NR activity through interconnected changes in photorespiration, carbohydrate-mediated feedback, redox regulation, source–sink dynamics, and nitrogen availability. While eCO₂ generally suppresses leaf nitrate assimilation by reducing photorespiratory support, root-zone CO₂ enrichment can transiently stimulate root NR activity, highlighting tissue-specific regulation. Multi-omics studies further demonstrate extensive metabolic and molecular reprogramming affecting carbon skeleton supply, amino acid biosynthesis, and nitrogen assimilation. In addition, NR-dependent NO production links nitrogen metabolism with stomatal regulation through ABA-independent H₂O₂–NO signaling. Despite these advances, the roles of NR phosphorylation, 14-3-3 protein interactions, and redox-mediated regulation under eCO₂ remain poorly understood. Overall, NR functions as a key metabolic and signaling hub coordinating carbon and nitrogen metabolism under future climate conditions. Understanding these regulatory mechanisms will facilitate strategies to improve nitrogen-use efficiency, sustain photosynthesis, and enhance tomato productivity under elevated atmospheric CO₂ while identifying priorities for future physiological, molecular, and multi-omics research. Full article

Plant-derived methane (CH₄) has already been reported, but the factors that regulate its production are not fully documented. Few studies have considered the effects of blue light on plant-derived CH₄, but the role of salicylic acid in the process has not been studied. We examined the effects of two blue light levels (0 and 4 mW cm⁻²) and two salicylic acid concentrations (0 and 100 μL of 1 mM solution every other day) on canola (Brassica napus) growth and CH₄ emissions by growing plants under the experimental conditions for 21 days. Blue light raised CH₄ emission by 184% and increased stem height, leaf area ratio, shoot–root mass ratio, nitrogen balance index, leaf water potential, soil water potential, and leaf water content, but decreased stem diameter, plant biomass, specific leaf mass, net CO₂ assimilation, photochemical quenching, photosynthetic pigments, flavonoids, and anthocyanins. Salicylic acid did not have a significant effect on plant traits. Methane had both positive and negative relationships with plant traits; for example, CH₄ was negatively correlated with plant dry mass (r = −0.776, p = 0.003), protective compounds (r = −0.914, p = 0.000) and stomatal density (r = −0.677, p = 0.016), but positively correlated with nitrogen balance index (r = 0.621, p = 0.031). Our findings suggest that blue light negatively affects canola growth but increases CH₄ emissions, whereas the application of salicylic acid, as described in this study, was insufficient for mitigating stress in plants. Full article

Trehalose-6-phosphate (T6P) is a key signalling metabolite that integrates carbon availability with development and stress responses in plants. T6P levels are controlled by trehalose phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) enzymes; however, while TPS enzymes have been studied extensively, the physiological functions of individual TPPs remain incompletely understood. Here, we investigated the role of TPPI in Arabidopsis using loss-of-function tppi mutants, a complemented line (tppi+35S::TPPI), and TPPI-overexpressing (TPPI-OEX) plants. The tppi mutant exhibited delayed flowering accompanied by reduced expression of CO, FT, and SPL3, while complementation restored wild-type (WT) flowering time. TPPI-OEX plants displayed an intermediate flowering phenotype with moderate reductions in CO and FT expression. Under nitrogen starvation, tppi plants showed enhanced anthocyanin accumulation, altered nitrate reductase regulation, characterised by lower total enzyme activity but a higher activation state, and enhanced expression of nitrate assimilation and uptake genes (NIA1, NIA2, NRT1.1, and NRT2.1). TPPI deficiency also altered photosynthetic performance, with enhanced photosystem I (PSI) acceptor-side limitation, increased non-photochemical quenching (NPQ), and a tendency toward reduced photosystem II (PSII) electron transport, indicating altered photosynthetic electron transport and energy dissipation. Taken together, these results indicate that TPPI contributes to the regulation of flowering time, nitrogen responses, and photosynthetic performance, suggesting broader effects of TPPI on plant developmental and physiological processes. Full article

Soil salinity is an increasing constraint to crop production, yet little is known about the responses of culantro (Eryngium foetidum), a medicinal and culinary species of high economic value, to saline conditions. This study evaluated the effects of NaCl-induced salinity (0, 40, and 80 mM) on the growth, photosynthetic performance, pigment content, and vascular anatomy of E. foetidum cultivated in vitro. After 45 days, salinity significantly reduced shoot and root length, leaf number, chlorophyll fluorescence, net CO₂ assimilation, stomatal conductance, transpiration, carboxylation efficiency, and the contents of chlorophylls a and b, and carotenoids, with the strongest effects observed at 80 mM NaCl. In contrast, leaf area, biomass accumulation, specific leaf area, and intrinsic water-use efficiency were not significantly affected. Qualitative anatomical observations indicated apparent modifications in vascular organization under saline conditions, including narrower xylem vessels and phloem disorganization. Collectively, these findings demonstrate that salinity primarily impairs photosynthetic performance and vegetative growth while inducing morphological, physiological, and apparent anatomical responses in E. foetidum cultivated in vitro. This study provides the first integrated characterization of the responses of E. foetidum to in vitro salt stress, establishing a foundation for future investigations into the physiological mechanisms underlying salinity responses in this species. Full article

Leaf senescence progressively remodels the photosynthetic apparatus, leading to impaired electron transport and declining carbon assimilation. Here, we investigated how dark-induced senescence (DIS) and exogenous 6-benzyladenine (BA) affect photosystem function, cyclic electron flow (CEF), photosynthetic protein remodeling and CO₂ assimilation in two barley (Hordeum vulgare L.) cultivars differing in their senescence characteristics, Carina (spring) and Lomerit (winter). DIS markedly reduced the chlorophyll content, PSI and PSII photochemistry, electron transport and CO₂ assimilation in both cultivars, although the underlying mechanisms differed. Carina maintained higher CEF despite stronger PSII inhibition, whereas Lomerit exhibited a greater decline in CEF accompanied by stronger donor- and acceptor-side limitations of PSI. These physiological responses coincided with the selective remodeling of proteins forming the PSI-associated electron transport network, including coordinated changes in cytochrome f, PGRL1, NdhS, FNR and photosystem antenna proteins, indicating the functional reorganization of photosynthetic electron transport rather than uniform chloroplast protein degradation. BA delayed senescence by preserving chlorophyll, maintaining PSI and PSII activity, sustaining CEF and partially alleviating the decline in CO₂ assimilation. The protective effects of BA were more pronounced in Carina and coincided with the more effective preservation of proteins associated with PSI-dependent electron transport. Collectively, our findings identify the selective stabilization of the PSI-associated electron transport network as a central mechanism underlying cytokinin-mediated delay of leaf senescence in barley and demonstrate that cultivar-dependent regulation of this network determines the effectiveness of cytokinin-mediated protection of photosynthesis. Full article

Microalgal growth-promoting bacteria (MGPBs) represent a promising strategy to enhance biomass productivity, yet the mechanistic basis of these mutualistic interactions remains poorly understood. Here, we isolated a new MGPB, Cupriavidus oxalaticus MEYA8, and characterized its mutualistic interaction with the model microalga Chlamydomonas reinhardtii. Co-cultivation at an optimal MEYA8: Chlamydomonas ratio greatly enhanced microalgal cell density and chlorophyll content, which reached 2.1-fold and 1.6-fold those of the control, respectively, with markedly improved photosynthetic efficiency across both photosystems. Transwell assays confirmed that this promotion is mediated by diffusible metabolites rather than direct cell contact. Metabolites and multi-omics analyses revealed that MEYA8 can produce compounds similar to indole-3-acetic acid (IAA) and is adapted to the microalgal phycosphere by preferentially utilizing organic acids and amino acid derivatives. In response, Chlamydomonas upregulated proteins involved in photosynthetic electron transport, energy metabolism, and nitrogen assimilation, consistent with the observed enhancement in photosynthetic performance. These findings suggest a metabolically reciprocal interaction model: MEYA8 supplies diffusible growth-promoting factors such as IAA-like compounds to enhance Chlamydomonas photosynthesis and growth, while Chlamydomonas provides organic substrates that sustain bacterial proliferation. Our work provides new insights into algal–bacterial mutualism and may provide a new microbial resource for engineering microalgal and beneficial bacterial consortia. Full article

The assimilation capacity of the biosphere and the sustainability of the living resources are enhanced by the efficient and continued contribution of the vegetation from all ecoregions of the Earth. The urban greenery fulfills many regulatory ecosystem services (RES) as well. In this regard, the importance of urban green spaces (UGS) in helping to reduce the adverse impacts of overcrowding and changing climate is of pertinence. Lack of quantitative information from urban settings in different climatic regions seriously constrains the recognition of the important role UGS play in carbon storage and sequestration. To assess how the UGS is aiding the retention of carbon, which is photosynthetically assimilated into biomass and/or sequestered, relevant field parameters were collected from 4010 trees belonging to 34 different species, different hedge plants, and groundcover grasses spread in 24,991 m² area in three parks of Panaji city, India. Standard methods were followed to derive carbon stock and sequestration rates by trees, hedge plants, and groundcover. Notwithstanding wide differences between tree species, the weighted mean of CO₂ sequestered per tree averaged 55 kg y⁻¹ (ca. 78.82 tons ha⁻¹) in Panaji city. Accordingly, the CO₂ sequestration potential of trees, in the UGS of Panaji (by 76,751 trees) and Tumkur (with an estimated 38,152 trees) cities, respectively, was 4221.31 tons y⁻¹ ha⁻¹ and 2098 tons ha⁻¹ y⁻¹ @ 55 kg tree⁻¹ y⁻¹. It is apparent from this first-time study that calculated tree carbon biomass and species-wise yearly carbon sequestration rates (CSRs) of 78.82 tons ha⁻¹ y⁻¹ and that of carbon production rates of 31.77 tons ha⁻¹ y⁻¹ are far higher than the previously reported CSR estimates variously from 1 to 8 tons ha⁻¹ y⁻¹ and carbon production rates 3.23 to 6.55 tons ha⁻¹ y⁻¹. The hedge row carbon biomass averaged 13.18 tons ha⁻¹ and sequestration of 48.38 tons ha⁻¹ y⁻¹ CO₂. Similarly, occupying over 42% of the UGS, the groundcover carbon biomass averaged 14.69 tons ha⁻¹ with sequestration of 53.92 tons CO₂ ha⁻¹ y⁻¹. Combined CSP of existing trees, groundcover, and hedge plants in Panaji and Tumkur city UGS apparently neutralize carbon footprint of over 4550 and 2200 Indians at an annual per capita emission of 1.94-ton. It is thus undeniable that in our global fight against climate change, the addition of inputs and data from studies like these can aid in planning mitigation measure as well as in fulfilling local/regional sustainability plans and needs. Full article

Most Citrus spp. trees in China are cultivated in acidic soils with low soil organic matter and high Al³⁺. The mechanisms of humic acid (HA) to alleviate Al³⁺ stress in plants remain unclear. ‘Sour pummelo’ (Citrus grandis (L.) Osbeck) seedlings were exposed to 0.5 (HA0.5), 0.1 (HA0.1), or 0 (HA0) mM sodium humate and 1.2 (Al1.2) or 0 (Al0) mM AlCl₃·6H₂O for 128 days. Thereafter, the research examined biomass; Al and mineral nutrients; leaf photosynthetic performance; and leaf and root nonstructural carbohydrates, reactive oxygen species metabolism, and related physiological parameters. Al1.2 significantly reduced whole plant dry weight (DW), root DW, leaf CO₂ assimilation (A_CO2), and chlorophyll a + b concentration by 61%, 45%, 61%, and 35%, respectively, at HA0, but only 48%, 17%, 44%, and 11%, respectively, at HA0.5. Further analysis suggested that the addition of HA endowed Citrus with Al resilience by the following several aspects: (a) lessened tissue (leaf, stem, and root) concentrations of Al and enhanced capacity to maintain macronutrient (S, K, Mg, Ca, N, and P) homeostasis at Al1.2; (b) improved capacity to combat oxidative stress at Al1.2; and (c) enhanced A_CO2 and growth at Al1.2. Further analysis indicated that HA-mediated alleviation of growth decline caused by Al1.2 involved (a) reduced ability to absorb Al and less root-to-shoot Al transport and (b) increased ability to maintain macronutrient homeostasis and to combat oxidative stress; and that HA-mediated alleviation of leaf chlorophyll and A_CO2 decline and photosynthetic electron transport chain impairment involved less leaf Al concentration and improved leaf macronutrient homeostasis. To conclude, the addition of HA lowered roots’ ability to absorb Al and tissue Al concentration and subsequently mitigated Al-toxic impairment to root growth and function, thereby enhancing the ability of plants to maintain macronutrient homeostasis, and hence alleviating Al1.2-stimulated oxidative damage and inhibition of A_CO2 and growth. Full article

The frequency and magnitude of droughts are increasing concurrently with atmospheric CO₂ concentration, with profound consequences for plant carbon assimilation. However, the interactions and the underlying physiological mechanism are still not fully understood. To fill the knowledge gap, we exposed Chinese fir (Cunninghamia lanceolata) saplings to two CO₂ concentrations (400 and 800 ppm, representing ambient and elevated CO₂) and two soil water regimes (70% and 40% field capacity; well-watered and drought-stressed conditions) in a factorial design. Net photosynthetic rate (A_n), chlorophyll fluorescence, photosynthetic pigments, oxidative stress indicators, and antioxidant enzyme activities were measured four times over a 45-day treatment period. Under well-watered conditions, elevated CO₂ significantly increased A_n by 61.5%. However, drought stress substantially reduced A_n by 75.0% under ambient CO₂ and by 75.6% under elevated CO₂, whereas no statistically significant CO₂-induced increase was detected under drought conditions. Furthermore, drought stress caused marked reductions in stomatal conductance, transpiration, chlorophyll content, and photosystem II (PSII)-related parameters, together with increased malondialdehyde, proline, and antioxidant enzyme activities. Variance partitioning analysis suggested that stomatal regulation (SR), photosynthetic capacity (PC), and stress response (STR) jointly explained 71% of the variation in A_n. Structural equation modeling further suggested that drought stress restricted the photosynthetic benefits of elevated CO₂ primarily through stomatal closure, concurrently associated with stress-related declines in pigment stability and photochemical performance. These findings suggest that the carbon sink potential of Chinese fir plantations under future CO₂-enriched climates may be strongly constrained by water deficits. Full article

Water scarcity caused by irregular rainfall and high evapotranspiration rates in the Brazilian semi-arid region is one of the main factors limiting watermelon cultivation, underscoring the need for irrigation strategies capable of mitigating the adverse effects of water deficit. This study aimed to evaluate the effects of foliar salicylic acid application on the induction of water-deficit tolerance in watermelon plants subjected to water restriction at different phenological stages under semi-arid conditions. The experiment was conducted using a randomized block design in a split-plot arrangement, with five irrigation management strategies based on crop evapotranspiration (ETc) and four salicylic acid (SA) concentrations, with three replications and three plants per plot. Water deficit adversely affected the morphophysiological traits of the plants and the physical and chemical attributes of ‘Crimson Sweet’ watermelon fruits, with water restriction during the vegetative and flowering stages causing the most severe effects. Foliar application of salicylic acid at concentrations ranging from 1.2 to 2.6 mM increased relative water content by 9.4%, reduced electrolyte leakage by 11.60%, and enhanced CO₂ assimilation by 18.82%, instantaneous water-use efficiency in 128.10%, and instantaneous carboxylation efficiency by 46.92%. Salicylic acid concentrations within this range also improved plant water status, gas exchange, photosynthetic pigment content, growth, and the physical and chemical attributes of the fruits. In contrast, concentrations above 2.6 mM reduced gas exchange, photosynthetic pigment accumulation, chlorophyll a fluorescence, and the physical and chemical quality of ‘Crimson Sweet’ watermelon fruits. Thus, salicylic acid may be an alternative to modulate the tolerance of watermelon plants under water deficit during phenological phases. Full article

The aim of study was to investigate the effects of foliar application of salicylic acid on cellular damage, physiological indices, and growth of dwarf cashew cultivated under salt stress. A 5 × 4 factorial scheme, resulting from the combination of five ECiw levels (0.4, 1.2, 2.0, 2.8, and 3.6 dS m⁻¹) and four salicylic acid concentrations (control—0, 1, 2, and 3 mM), with three replications. Irrigation water salinity of 3.6 dS m⁻¹ inhibited the synthesis of photosynthetic pigments, gas exchange, chlorophyll a fluorescence, and the growth of dwarf cashew plants. Foliar application of salicylic acid at concentrations ranging from 0.1 to 2.5 mM mitigated the effects of salt stress on relative water content, stomatal conductance, internal CO₂ concentration, CO₂ assimilation rate, instantaneous carboxylation efficiency, variable fluorescence, quantum efficiency of photosystem II, stem diameter at the grafting point, and plant height, while also reducing electrolyte leakage and initial fluorescence in dwarf cashew plants at 180 days after transplanting. Salicylic acid (SA), when applied at appropriate concentrations, alleviates the deleterious effects of salt stress on the growth and physiological performance of dwarf cashew plants. Full article

Usnic acid (UA) is a secondary metabolite produced by lichens that has attracted interest because of its antimicrobial, photoprotective, and antioxidant properties, suggesting its potential use as a biostimulant in agriculture. However, its evaluation in agricultural crops is limited. In the present study, we evaluated the effect of applying (+) UA on enzymatic and non-enzymatic antioxidant systems, photosynthetic pigments, photosynthetic enzyme activity, and markers of oxidative stress in “Albion” strawberry plants. The plants were grown in a peat moss:perlite substrate (1:1, v/v) and cultivated under tunnel greenhouse conditions using a nutrient solution applied via fertigation. (+) UA was applied at 400 µg/mL via three routes (foliar, drench, and a combination of foliar and drench) on three occasions. Leaf tissue was collected 117 days after transplantation, and the biochemical parameters were quantified. (+) UA increased the activity of glutathione peroxidase (GPX) (53% via foliar-drench) and catalase (CAT) by 73.5% (via drench), and reduced glutathione (GSH) content by 58% (via foliar). β-carbonic anhydrase (βCA) activity increased by 415% and 384% (foliar and foliar-drench, respectively). Likewise, Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) activity increased by 58.23% (drench) and phosphoenolpyruvate carboxylase (PEPC) by 25% and 46% (foliar and drench), suggesting positive effects on the processes associated with CO₂ assimilation and transport. In contrast, no significant changes were observed in the levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), or proline, indicating the absence of oxidative stress. These findings suggest that (+) UA modulates the enzymatic antioxidant system, promoting favorable physilogical responses without inducing oxidative stress. The use of (+) UA has been proposed as a potential promoter of metabolism in agricultural crops. In addition, new avenues of research are being explored to investigate the role in modulating antioxidant responses under biotic and abiotic stress conditions. Full article