Reactive oxygen species, oxidative signaling and the regulation of photosynthesis

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

Potential role of tocopherol in protecting crop plants against abiotic stresses

The changing global climate have given rise to abiotic stresses that adversely affect the metabolic activities of plants, limit their growth, and agricultural output posing a serious threat to food production. The abiotic stresses commonly lead to production of reactive oxygen species (ROS) that results in cellular oxidation. Over the course of evolution, plants have devised efficient enzymatic and non-enzymatic anti-oxidative strategies to counteract harmful effects of ROS. Among the emerging non-enzymatic anti-oxidative technologies, the chloroplast lipophilic antioxidant vitamin A (Tocopherol) shows great promise. Working in coordination with the other cellular antioxidant machinery, it scavenges ROS, prevents lipid peroxidation, regulates stable cellular redox conditions, simulates signal cascades, improves membrane stability, confers photoprotection and enhances resistance against abiotic stresses. The amount of tocopherol production varies based on the severity of stress and its proposed mechanism of action involves arresting lipid peroxidation while quenching singlet oxygen species and lipid peroxyl radicals. Additionally, studies have demonstrated its coordination with other cellular antioxidants and phytohormones. Despite its significance, the precise mechanism of tocopherol action and signaling coordination are not yet fully understood. To bridge this knowledge gap, the present review aims to explore and understand the biosynthesis and antioxidant functions of Vitamin E, along with its signal transduction and stress regulation capacities and responses. Furthermore, the review delves into the light harvesting and photoprotection capabilities of tocopherol. By providing insights into these domains, this review offers new opportunities and avenues for using tocopherol in the management of abiotic stresses in agriculture.

Enzyme-based kinetic modelling of ASC-GSH cycle during tomato fruit development reveals the importance of reducing power and ROS availability

The ascorbate-glutathione (ASC-GSH) cycle is at the heart of redox metabolism, linking the major redox buffers with central metabolism through the processing of reactive oxygen species (ROS) and pyridine nucleotide metabolism. Tomato fruit development is underpinned by changes in redox buffer contents and their associated enzyme capacities, but interactions between them remain unclear. Based on quantitative data obtained for the core redox metabolism, we built an enzyme-based kinetic model to calculate redox metabolite concentrations with their corresponding fluxes and control coefficients. Dynamic and associated regulations of the ASC-GSH cycle throughout the whole fruit development were analysed and pointed to a sequential metabolic control of redox fluxes by ASC synthesis, NAD(P)H and ROS availability depending on the developmental phase. Furthermore, we highlighted that monodehydroascorbate reductase and the availability of reducing power were found to be the main regulators of the redox state of ASC and GSH during fruit growth under optimal conditions. Our kinetic modelling approach indicated that tomato fruit development displayed growth phase-dependent redox metabolism linked with central metabolism via pyridine nucleotides and H2 O2 availability, while providing a new tool to the scientific community to investigate redox metabolism in fruits.

Effectiveness of silver nitrate application on plant growth and bioactive compounds in Agastache rugosa (Fisch. & C.A.Mey.) kuntze

The objective of this study was to determine the optimal dose of silver nitrate (AgNO3) for plant growth and to increase the main bioactive compounds in A. rugosa cultivated in a hydroponic system. The application of soaked diniconazole (120 μmol mol-1) to all plants at 7 days after transplanting (DAT) for dwarfing plant height, optimizing cultivation space in the plant factory. Subsequently, plants were soaked with 50, 100, 200, and 400 μmol mol-1 AgNO3 for 10 min at 25 DAT and harvested at 39 DAT. The results indicated that 200 and 400 μmol mol-1 treatments tended to severely decrease plant growth parameters compared to treatments with lower concentrations. The net photosynthetic rate was significantly reduced by the 200 and 400 μmol mol-1 treatments compared to treatments with other concentrations. The 400 μmol mol-1 treatment led to the lowest concentrations of chlorophyll a, chlorophyll a/b, total carotenoid, chlorophyll b, and the total chlorophyll. However, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was considerably increased in 50, 100, 200, and 400 μmol mol-1 compared to that of the control plants. A higher rosmarinic acid (RA) concentration in the whole plant was noticed with the 400 μmol mol-1 treatment compared with that of the untreated plants. The 100 μmol mol-1 treatment exhibited the highest concentration and content of tilianin in the whole plant. Concentration of acacetin 1 significantly increased in the whole plant with 100 and 200 μmol mol-1 treatments compared with that of the untreated plants. Concentrations of acacetin 2 and 3 in the whole plant were the highest with 100 and 200 μmol mol-1 treatments, respectively. The results demonstrated that 100 μmol mol-1 treatments can be used to increase bioactive compounds without severely limiting the plant growth and reducing chlorophyll concentrations of A. rugosa. Implementing this optimal dose can enable growers and researchers to cultivate A. rugosa more efficiently, enhancing bioactive compound content and overall plant performance, thus harnessing the potential health benefits of this valuable plant species.

Evaluation of secondary sexual dimorphism of the dioecious Amaranthus palmeri under abiotic stress

The evolution of secondary sex-specific traits of dioecious species under abiotic stress conditions has received limited research, especially in the case of Amaranthus palmeri, a fast adapting and highly competing plant. Here, we have examined the interactive effects of abiotic stress on mineral accumulation, chlorophyll a and b content, and the operating capacity of Photosystem II (PSII) in both male and female A. palmeri plants grown under three different intensities of white light, and under N, K or P deficiency. Mineral profiling of the leaves and stems (with inflorescence) highlighted intra- and intersexual differences in their accumulation pattern and mineral associations. Chlorophyll a and chlorophyll b were different between the male and the female plants, being slightly lower in the latter, at high light intensity towards maturity, or under K or P deficiency. Further, slight, although statistically significant differences were recorded in the chlorophyll a/b ratio, which was lower at the higher light intensity in the female, over that in the male, plants towards maturity. Chlorophyll fluorescence parameters, i.e., steady state and maximum fluorescence increased under high light intensity, whereas the PSII operating efficiency decreased in the female plants, indicating reduced PSII capacity. Sex-specific differences in A. palmeri showed a differential response to stressful conditions because of differences in their ontogeny and physiology, and possibly due to the cost of reproduction. We suggest that the breeding system of dioecious species has weaknesses that can be used for the ecological management of dioecious weeds without relying on the use of herbicides.

Hydrogen peroxide signal photosynthetic acclimation of Solanum lycopersicum L. cv Micro-Tom under water deficit

The current climate change setting necessitates the development of methods to mitigate the effects of water scarcity to ensure the sustainability of agricultural activities.f Hydrogen peroxide (H2O2) is a plant signaling molecule that can trigger metabolic defense mechanisms in response to adverse environmental circumstances like as drought. The purpose of this study was to investigate if foliar application of H2O2 stimulates modifications in photosynthetic metabolism for adaptation of tomato plants to a period of water deficit and recovery. The study, which was carried out in a factorial scheme, tested plants subjected to two water conditions (well-watered plants and plants subjected to water deficit), as well as foliar application of 1 mM H2O2 (zero, one, or two applications, 24 h after the first), and was evaluated in two moments, during the deficit period and after recovery. Foliar application of 1 mM H2O2 resulted in a 69% increase in the maximum rate of RuBisCO carboxylation in well-watered plants, contributing to tomato photosynthetic adjustment. H2O2 treatment resulted in a 37% increase in dry mass in these plants. In plants subjected to water deficiency, 2× H2O2 increased stress tolerance by reducing the maximal rate of RuBisCO carboxylation by only 18%, but in plants that did not receive H2O2 treatment, the reduction was 86% in comparison to the wet plants. Plants exposed to a water shortage and given 2× H2O2 stored sucrose in the leaves and had a 17% higher relative water content than plants not given H2O2. Thus, H2O2 foliar treatment can be used in tomato management to induce drought tolerance or to boost photosynthetic activity and dry mass formation in well-watered plants.

Transcriptomic approach to uncover dynamic events in the development of mid-season sunburn in apple fruit

Apples grown in high heat, high light, and low humidity environments are at risk for sun injury disorders like sunburn and associated crop losses. Understanding the physiological and molecular mechanisms underlying sunburn will support improvement of mitigation strategies and breeding for more resilient varieties. Numerous studies have highlighted key biochemical processes involved in sun injury, such as the phenylpropanoid and reactive oxygen species (ROS) pathways, demonstrating both enzyme activities and expression of related genes in response to sunburn conditions. Most previous studies have focused on at-harvest activity of a small number of genes in response to heat stress. Thus, it remains unclear how stress events earlier in the season affect physiology and gene expression. Here, we applied heat stress to mid-season apples in the field and collected tissue along a time course-24, 48, and 72 h following a heat stimulus-to investigate dynamic gene expression changes using a transcriptomic lens. We found a relatively small number of differentially expressed genes (DEGs) and enriched functional terms in response to heat treatments. Only a few of these belonged to pathways previously described to be involved in sunburn, such as the AsA-GSH pathway, while most DEGs had not yet been implicated in sunburn or heat stress in pome fruit.

Early-Stage Detection of Biotic and Abiotic Stress on Plants by Chlorophyll Fluorescence Imaging Analysis

Most agricultural land, as a result of climate change, experiences severe stress that significantly reduces agricultural yields. Crop sensing by imaging techniques allows early-stage detection of biotic or abiotic stress to avoid damage and significant yield losses. Among the top certified imaging techniques for plant stress detection is chlorophyll a fluorescence imaging, which can evaluate spatiotemporal leaf changes, permitting the pre-symptomatic monitoring of plant physiological status long before any visible symptoms develop, allowing for high-throughput assessment. Here, we review different examples of how chlorophyll a fluorescence imaging analysis can be used to evaluate biotic and abiotic stress. Chlorophyll a is able to detect biotic stress as early as 15 min after Spodoptera exigua feeding, or 30 min after Botrytis cinerea application on tomato plants, or on the onset of water-deficit stress, and thus has potential for early stress detection. Chlorophyll fluorescence (ChlF) analysis is a rapid, non-invasive, easy to perform, low-cost, and highly sensitive method that can estimate photosynthetic performance and detect the influence of diverse stresses on plants. In terms of ChlF parameters, the fraction of open photosystem II (PSII) reaction centers (qp) can be used for early stress detection, since it has been found in many recent studies to be the most accurate and appropriate indicator for ChlF-based screening of the impact of environmental stress on plants.

Physiological and Agronomic Responses and Nutrient Uptake of Soybean Genotypes Cultivated Under Various Sowing Dates

Late or early sowing subjecting crop plants to stress conditions, this is simulating the climatic change effects. The global warming and climate change are critical issues in agriculture since progressive rise in temperature leads to exposure the crops to heat stress, hence low productivity. Since weather conditions are uncontrollable, it is impossible to modulate their negative impacts against crop growth and development. However, scientists should not be handcuffed about this serious problem. So, in open field conditions, the performance of some soybean genotypes was evaluated under different sowing dates. Along the two seasons of 2019 and 2020, field experiments were designed in a split-plot design using three replicates to evaluate the performance of four soybean genotypes (Giza-21, Giza-35, Giza-111, and Crawford) under four sowing dates (15th April, 30th April, 15th May, and 30th May). Various physiological and growth traits, yield attributes, seed nutrient contents, and oil and protein contents were estimated. Sowing Crawford (in both seasons) and Giza-35 (in the first season) on 15th April as well as Giza-111 either on 30th April or 15th May produced the highest catalase activity. In plots sown on 30th April, Crawford and Giza-21 (in the first season) and Giza-111 (in both seasons) exhibited the highest leaves area plant−1. Plots sown by Giza-111 on 30th April was the potent interaction for enhancing seed yield in both seasons. Under any sowing date in the second season and the sowing date of 30th April in the first season, Giza-111 was the effective genotype for recording the maximum seed oil content. For adopting a specific stress condition scenario, it is advisable to insert Giza-111 as an effective gene pool to improve soybean genotypes under unfavorable conditions, expressed in sowing dates.

The Splicing Factor SR45 Negatively Regulates Anthocyanin Accumulation under High-Light Stress in Arabidopsis thaliana

High-intensity light (HL) greatly induces the accumulation of anthocyanin, a fundamental compound in photoprotection and antioxidation. Many mechanisms regulating anthocyanin biosynthesis are well-characterized across developmental and environmental conditions; however, post-transcriptional regulation of its biosynthesis remains unclear. RNA splicing is one mechanism of post-transcriptional control and reprogramming in response to different developmental cues and stress conditions. The Arabidopsis splicing modulator SR45 regulates a number of developmental and environmental stress responses. Here, we investigated the role of SR45 and its isoforms in HL-induced anthocyanin accumulation. We found that the SR45 promoter contains light-responsive cis-elements, and that light stress significantly increases SR45 expression. Furthermore, we found that mutant plants lacking SR45 function (sr45) accumulate significantly more anthocyanin under HL. SR45 is alternatively spliced to produce two proteins, SR45.1 and SR45.2, which differ by seven amino acids. Intriguingly, these isoforms exhibited distinct functions, with only SR45.1 reversing anthocyanin accumulation in the sr45 plants. We also identified possible SR45 target genes that are involved in anthocyanin synthesis. Consistent with the antioxidant role of anthocyanin, we found that sr45 mutants and SR45.2 overexpression lines accumulate anthocyanin and better tolerate paraquat which induces oxidative stress. Collectively, our results reveal that the Arabidopsis splicing regulator SR45 inhibits anthocyanin accumulation under HL, which may negatively affect oxidative stress tolerance. This study illuminates splicing-level regulation of anthocyanin production in response to light stress and offers a possible target for genetic modification to increase plant stress tolerance.

RCD1 Promotes Salt Stress Tolerance in Arabidopsis by Repressing ANAC017 Activity

Plants have evolved diverse strategies to accommodate saline environments. More insights into the knowledge of salt stress regulatory pathways will benefit crop breeding. RADICAL-INDUCED CELL DEATH 1 (RCD1) was previously identified as an essential player in salt stress response. However, the underlying mechanism remains elusive. Here, we unraveled that Arabidopsis NAC domain-containing protein 17 (ANAC017) acts downstream of RCD1 in salt stress response, and its ER-to-nucleus transport is triggered by high salinity. Genetic and biochemical evidence showed that RCD1 interacts with transmembrane motif-truncated ANAC017 in the nucleus and represses its transcriptional activity. Transcriptome analysis revealed that genes associated with oxidation reduction process and response to salt stress are similarly dysregulated in loss-of-function rcd1 and gain-of-function anac017-2 mutants. In addition, we found that ANAC017 plays a negative role in salt stress response by impairing the superoxide dismutase (SOD) enzyme activity. Taken together, our study uncovered that RCD1 promotes salt stress response and maintains ROS homeostasis by inhibiting ANAC017 activity.

Insights into the binding mechanism of ascorbic acid and violaxanthin with violaxanthin de-epoxidase (VDE) and chlorophycean violaxanthin de-epoxidase (CVDE) enzymes

Photosynthetic organisms have evolved to work under low and high lights in photoprotection, acting as a scavenger of reactive oxygen species. The light-dependent xanthophyll cycle involved in this process is performed by a key enzyme (present in the thylakoid lumen), Violaxanthin De-Epoxidase (VDE), in the presence of violaxanthin (Vio) and ascorbic acid substrates. Phylogenetically, VDE is found to be connected with an ancestral enzyme Chlorophycean Violaxanthin De-Epoxidase (CVDE), present in the green algae on the stromal side of the thylakoid membrane. However, the structure and functions of CVDE were not known. In search of functional similarities involving this cycle, the structure, binding conformation, stability, and interaction mechanism of CVDE are explored with the two substrates compared to VDE. The structure of CVDE was determined by homology modeling and validated. In silico docking (of first-principles optimized substrates) revealed it has a larger catalytic domain than VDE. A thorough analysis of the binding affinity and stability of four enzyme-substrate complexes is performed by computing free energies and their decomposition, the root-mean-square deviation (RMSD) and fluctuation (RMSF), the radius of gyration, salt bridge, and hydrogen bonding interactions in molecular dynamics. Based on these, violaxanthin interacts with CVDE to a similar extent as that of VDE. Hence, its role is expected to be the same for both enzymes. On the contrary, ascorbic acid has a weaker interaction with CVDE than VDE. Given these interactions drive epoxidation or de-epoxidation in the xanthophyll cycle, it immediately discerns that either ascorbic acid does not participate in de-epoxidation or a different cofactor is necessary as CVDE has a weaker interaction with ascorbic acid than VDE.

Autophagy and multivesicular body pathways cooperate to protect sulfur assimilation and chloroplast functions

Autophagy and multivesicular bodies (MVBs) represent 2 closely related lysosomal/vacuolar degradation pathways. In Arabidopsis (Arabidopsis thaliana), autophagy is stress-induced, with deficiency in autophagy causing strong defects in stress responses but limited effects on growth. LYST-INTERACTING PROTEIN 5 (LIP5) is a key regulator of stress-induced MVB biogenesis, and mutation of LIP5 also strongly compromises stress responses with little effect on growth in Arabidopsis. To determine the functional interactions of these 2 pathways in Arabidopsis, we generated mutations in both the LIP5 and AUTOPHAGY-RELATED PROTEIN (ATG) genes. atg5/lip5 and atg7/lip5 double mutants displayed strong synergistic phenotypes in fitness characterized by stunted growth, early senescence, reduced survival, and greatly diminished seed production under normal growth conditions. Transcriptome and metabolite analysis revealed that chloroplast sulfate assimilation was specifically downregulated at early seedling stages in the atg7/lip5 double mutant prior to the onset of visible phenotypes. Overexpression of adenosine 5'-phosphosulfate reductase 1, a key enzyme in sulfate assimilation, substantially improved the growth and fitness of the atg7/lip5 double mutant. Comparative multi-omic analysis further revealed that the atg7/lip5 double mutant was strongly compromised in other chloroplast functions including photosynthesis and primary carbon metabolism. Premature senescence and reduced survival of atg/lip5 double mutants were associated with increased accumulation of reactive oxygen species and overactivation of stress-associated programs. Blocking PHYTOALEXIN DEFICIENT 4 and salicylic acid signaling prevented early senescence and death of the atg7/lip5 double mutant. Thus, stress-responsive autophagy and MVB pathways play an important cooperative role in protecting essential chloroplast functions including sulfur assimilation under normal growth conditions to suppress salicylic-acid-dependent premature cell-death and promote plant growth and fitness.

Chitosan oligomers (COS) trigger a coordinated biochemical response of lemongrass (Cymbopogon flexuosus) plants to palliate salinity-induced oxidative stress

Plant susceptibility to salt depends on several factors from its genetic makeup to modifiable physiological and biochemical status. We used lemongrass (Cymbopogon flexuosus) plants as a relevant medicinal and aromatic cash crop to assess the potential benefits of chitosan oligomers (COS) on plant growth and essential oil productivity during salinity stress (160 and 240 mM NaCl). Five foliar sprays of 120 mg L^-1 of COS were applied weekly. Several aspects of photosynthesis, gas exchange, cellular defence, and essential oil productivity of lemongrass were traced. The obtained data indicated that 120 mg L^-1 COS alleviated photosynthetic constraints and raised the enzymatic antioxidant defence including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities that minimised salt-induced oxidative damage. Further, stomatal conductance (g_s) and photosynthetic CO₂ assimilation (A) were improved to support overall plant development. The same treatment increased geraniol dehydrogenase (GeDH) activity and lemongrass essential oil production. COS-induced salt resilience suggests that COS could become a useful biotechnological tool in reclaiming saline soil for improved crop productivity, especially when such soil is unfit for leading food crops. Considering its additional economic value in the essential oil industry, we propose COS-treated lemongrass as an excellent alternative crop for saline lands.

Inoculation with Actinobacteria spp. Isolated from a Hyper-Arid Environment Enhances Tolerance to Salinity in Lettuce Plants (Lactuca sativa L.)

Irrigated agriculture is responsible for a third of global agricultural production, but the overuse of water resources and intensification of farming practices threaten its sustainability. The use of saline water in irrigation has become an alternative in areas subjected to frequent drought, but this practice affects plant growth due to osmotic impact and excess of ions. Plant-growth-promoting rhizobacteria (PGPR) can mitigate the negative impacts of salinity and other abiotic factors on crop yields. Actinobacteria from the hyper-arid Atacama Desert could increase the plant tolerance to salinity, allowing their use as biofertilizers for lettuce crops using waters with high salt contents. In this work, rhizosphere samples of halophytic Metharme lanata were obtained from Atacama Desert, and actinobacteria were isolated and identified by 16S gene sequencing. The PGPR activities of phosphate solubilization, nitrogen fixation, and the production of siderophore and auxin were assessed at increasing concentrations of NaCl, as well as the enhancement of salt tolerance in lettuce plants irrigated with 100 mM of NaCl. Photosynthesis activity and chlorophyll content, proline content, lipid peroxidation, cation and P concentration, and the identification and quantification of phenolic compounds were assessed. The strains S. niveoruber ATMLC132021 and S. lienomycini ATMLC122021 were positive for nitrogen fixation and P solubilization activities and produced auxin up to 200 mM NaCl. In lettuce plants, both strains were able to improve salt stress tolerance by increasing proline contents, carotenoids, chlorophyll, water use efficiency (WUE), stomatal conductance (gs), and net photosynthesis (A), concomitantly with the overproduction of the phenolic compound dicaffeoylquinic acid. All these traits were positively correlated with the biomass production under saltwater irrigation, suggesting its possible use as bioinoculants for the agriculture in areas where the water resources are scarce and usually with high salt concentrations.

Impact of Ascorbic Acid on Zero-Valent Iron Nanoparticle and UV-B Mediated Stress in the Cyanobacterium, Fremyella diplosiphon

Fremyella diplosiphon is an ideal third-generation biofuel source due to its ability to produce transesterified lipids. While nanofer 25s zero-valent iron nanoparticles (nZVIs) improve lipid production, an imbalance between reactive oxygen species (ROS) and cellular defense can be catastrophic to the organism. In the present study, the effect of ascorbic acid on nZVI and UV-induced stress in F. diplosiphon strain B481-SD was investigated, and lipid profiles in the combination regimen of nZVIs and ascorbic acid compared. Comparison of F. diplosiphon growth in BG11 media amended with 2, 4, 6, 8, and 10 mM ascorbic acid indicated 6 mM to be optimal for the growth of B481-SD. Further, growth in 6 mM ascorbic acid combined with 3.2 mg/L nZVIs was significantly higher when compared to the combination regimen of 12.8 and 51.2 mg/L of nZVIs and 6 mM ascorbic acid. The reversal effect of UV-B radiation for 30 min and 1 h indicated that ascorbic acid restored B481-SD growth. Transesterified lipids characterized by gas chromatography-mass spectrometry indicated C16 hexadecanoate to be the most abundant fatty acid methyl ester in the combination regimen of 6 mM ascorbic acid and 12.8 mg/L nZVI-treated F. diplosiphon. These findings were supported by microscopic observations in which cellular degradation was observed in B481-SD cells treated with 6 mM ascorbic acid and 12.8 mg/L nZVIs. Our results indicate that ascorbic acid counteracts the damaging effect of oxidative stress produced by nZVIs.

Light-Dependent Regulatory Interactions between the Redox System and miRNAs and Their Biochemical and Physiological Effects in Plants

Light intensity and spectrum play a major role in the regulation of the growth, development, and stress response of plants. Changes in the light conditions affect the formation of reactive oxygen species, the activity of the antioxidants, and, consequently, the redox environment in the plant tissues. Many metabolic processes, thus the biogenesis and function of miRNAs, are redox-responsive. The miRNAs, in turn, can modulate various components of the redox system, and this process is also associated with the alteration in the intensity and spectrum of the light. In this review, we would like to summarise the possible regulatory mechanisms by which the alterations in the light conditions can influence miRNAs in a redox-dependent manner. Daily and seasonal fluctuations in the intensity and spectral composition of the light can affect the expression of miRNAs, which can fine-tune the various physiological and biochemical processes due to their effect on their target genes. The interactions between the redox system and miRNAs may be modulated by light conditions, and the proposed function of this regulatory network and its effect on the various biochemical and physiological processes will be introduced in plants.

An intrinsically disordered region-containing protein mitigates the drought-growth trade-off to boost yields

Drought stress poses a serious threat to global agricultural productivity and food security. Plant resistance to drought is typically accompanied by a growth deficit and yield penalty. Herein, we report a previously uncharacterized, dicotyledon-specific gene, Stress and Growth Interconnector (SGI), that promotes growth during drought in the oil crop rapeseed (Brassica napus) and the model plant Arabidopsis (Arabidopsis thaliana). Overexpression of SGI conferred enhanced biomass and yield under water-deficient conditions, whereas corresponding CRISPR SGI mutants exhibited the opposite effects. These attributes were achieved by mediating reactive oxygen species (ROS) homeostasis while maintaining photosynthetic efficiency to increase plant fitness under water-limiting environments. Further spatial-temporal transcriptome profiling revealed dynamic reprogramming of pathways for photosynthesis and stress responses during drought and the subsequent recovery. Mechanistically, SGI represents an intrinsically disordered region-containing protein that interacts with itself, catalase isoforms, dehydrins, and other drought-responsive positive factors, restraining ROS generation. These multifaceted interactions stabilize catalases in response to drought and facilitate their ROS-scavenging activities. Taken altogether, these findings provide insights into currently underexplored mechanisms to circumvent trade-offs between plant growth and stress tolerance that will inform strategies to breed climate-resilient, higher yielding crops for sustainable agriculture.

Transcriptomic and physiological properties reveal the tolerance mechanism to difenoconazole toxicity in wheat (Triticum aestivum L.)

Difenoconazole (DFZ) is a broad-spectrum fungicide widely applied in wheat production. However, excessive accumulation is linked to phytotoxicity. The effects of DFZ on plants and the response mechanisms to DFZ toxicity are poorly understood. Herein, the uptake, accumulation, and translocation of DFZ and induced changes in the morphology, physiology, and gene expression were investigated under hydroculture of roots treated with 50, 100, and 200 mg/L DFZ concentrations. Compared with the control, DEZ treatment upregulated the expression of genes encoding 4-coumarate-CoA ligase (4CL) and peroxidase (POD) involved in the lignin biosynthesis pathway and enhanced lignin biosynthesis. DFZ accumulated more in older leaves (cotyledons and lower true leaves), with 0.49-5.71 and 0.09-2.14 folds higher than levels in new upper leaves and roots, respectively. The excessive accumulation of DFZ in tissues was rapidly degraded, with a 15.7-69.3% reduction of DFZ content in roots and leaves from 3 DAT to 6 DAT. The genes expression and activity of glutathione S-transferase (GST) were increased. Furthermore, DFZ treatments upregulated genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and anthocyanidin synthase (ANS) involved in the flavonoid biosynthesis pathway and increased the amount of flavonoid and anthocyanins in leaves. This study provides new insights into the self-protective behaviors exhibited by wheat plants under DFZ stress. The mechanisms included hindering DFZ penetration from roots by enhancing lignin biosynthesis, accumulating more in old leaves, degrading by GST, and alleviating oxidative damage by increasing the content of flavonoids and anthocyanins in leaves.

Oxidative and Glycation Damage to Mitochondrial DNA and Plastid DNA during Plant Development

Oxidative damage to plant proteins, lipids, and DNA caused by reactive oxygen species (ROS) has long been studied. The damaging effects of reactive carbonyl groups (glycation damage) to plant proteins and lipids have also been extensively studied, but only recently has glycation damage to the DNA in plant mitochondria and plastids been reported. Here, we review data on organellar DNA maintenance after damage from ROS and glycation. Our focus is maize, where tissues representing the entire range of leaf development are readily obtained, from slow-growing cells in the basal meristem, containing immature organelles with pristine DNA, to fast-growing leaf cells, containing mature organelles with highly-fragmented DNA. The relative contributions to DNA damage from oxidation and glycation are not known. However, the changing patterns of damage and damage-defense during leaf development indicate tight coordination of responses to oxidation and glycation events. Future efforts should be directed at the mechanism by which this coordination is achieved.

Cadmium-induced oxidative stress responses and acclimation in plants require fine-tuning of redox biology at subcellular level

Cadmium (Cd) is one of the most toxic compounds released into our environment and is harmful to human health, urging the need to remediate Cd-polluted soils. To this end, it is important to increase our insight into the molecular mechanisms underlying Cd stress responses in plants, ultimately leading to acclimation, and to develop novel strategies for economic validation of these soils. Albeit its non-redox-active nature, Cd causes a cellular oxidative challenge, which is a crucial determinant in the onset of diverse signalling cascades required for long-term acclimation and survival of Cd-exposed plants. Although it is well known that Cd affects reactive oxygen species (ROS) production and scavenging, the contribution of individual organelles to Cd-induced oxidative stress responses is less well studied. Here, we provide an overview of the current information on Cd-induced organellar responses with special attention to redox biology. We propose that an integration of organellar ROS signals with other signalling pathways is essential to finetune plant acclimation to Cd stress.

Exogenous γ-aminobutyric acid (GABA) improves salt-inhibited nitrogen metabolism and the anaplerotic reaction of the tricarboxylic acid cycle by regulating GABA-shunt metabolism in maize seedlings

Salinity stress hampers the growth of most crop plants and reduces yield considerably. In addition to its role in metabolism, γ-aminobutyric acid (GABA) plays a special role in the regulation of salinity stress tolerance in plants, though the underlying physiological mechanism remains poorly understood. In order to study the physiological mechanism of GABA pathway regulated carbon and nitrogen metabolism and tis relationship with salt resistance of maize seedlings, we supplemented seedlings with exogenous GABA under salt stress. In this study, we showed that supplementation with 0.5 mmol·L^-1 (0.052 mg·g^-1) GABA alleviated salt toxicity in maize seedling leaves, ameliorated salt-induced oxidative stress, and increased antioxidant enzyme activity. Applying exogenous GABA maintained chloroplast structure and relieved chlorophyll degradation, thus improving the photosynthetic performance of the leaves. Due to the improvement in photosynthesis, sugar accumulation also increased. Endogenous GABA content and GABA transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH) activity were increased, while glutamate decarboxylase (GAD) activity was decreased, via the exogenous application of GABA under salt stress. Meanwhile, nitrogen metabolism and the tricarboxylic acid (TCA) cycle were activated by the supply of GABA. In general, through the regulation of GABA-shunt metabolism, GABA activated enzymes related to nitrogen metabolism and replenished the key substrates of the TCA cycle, thereby improving the balance of carbon and nitrogen metabolism of maize and improving salt tolerance.

Chlamydomonas mutants lacking chloroplast TRIOSE PHOSPHATE TRANSPORTER3 are metabolically compromised and light-sensitive

Modulation of photoassimilate export from the chloroplast is essential for controlling the distribution of fixed carbon in the cell and maintaining optimum photosynthetic rates. In this study we identified chloroplast TRIOSE PHOSPHATE/PHOSPHATE TRANSLOCATOR2 (CreTPT2) and CreTPT3 in the green alga Chlamydomonas (Chlamydomonas reinhardtii), which exhibit similar substrate specificities but whose encoding genes are differentially expressed over the diurnal cycle. We focused mostly on CreTPT3 because of its high level of expression and the severe phenotype exhibited by tpt3 relative to tpt2 mutants. Null mutants for CreTPT3 had a pleiotropic phenotype that affected growth, photosynthetic activities, metabolite profiles, carbon partitioning, and organelle-specific accumulation of H2O2. These analyses demonstrated that CreTPT3 is a dominant conduit on the chloroplast envelope for the transport of photoassimilates. In addition, CreTPT3 can serve as a safety valve that moves excess reductant out of the chloroplast and appears to be essential for preventing cells from experiencing oxidative stress and accumulating reactive oxygen species, even under low/moderate light intensities. Finally, our studies indicate subfunctionalization of the CreTPT transporters and suggest that there are differences in managing the export of photoassimilates from the chloroplasts of Chlamydomonas and vascular plants.

Comparative analysis of remediation efficiency and ultrastructural translocalization of polycyclic aromatic hydrocarbons in Medicago sativa, Helianthus annuus, and Tagetes erecta

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile anthropogenic contaminants that can damage soil fertility and threaten the environment due to their hazardous effects on various ecological parameters. The experimental objective was divided into two parts because PAHs are always present in mixtures. The toxicity of anthracene, phenanthrene, pyrene, and fluoranthene was examined and investigated the potential of three phytoremediator plants species viz Tagetes erecta, Helianthus annuus, and Medicago sativa for remediation and translocation of individual PAH. PAHs were shown to have inhibitory or stimulating effects on growth, antioxidant properties, and impact on the structure of plant cells. The result showed that M. sativa significantly enhances the removal rate of PAHs in the soil. The dissipation rate reached 96.2% in M. sativa planted soil, followed by H. annuus and T. erecta. Among the plant species, M. sativa exhibited the highest root and shoot concentrations (314.37 and 169.55 mg kg-1), while the lowest concentration was 187.56 and 76.60 mg kg-1 in T. erecta. SEM-EDX and fluorescence micrographs confirmed that pyrene altered plant tissue's ultrastructure and cell viability and was found to be the most toxic and resistant. M. sativa was proven to be the most effective plant for the mitigation of PAHs.

Exogenous calcium regulates the growth and development of Pinus massoniana detecting by physiological, proteomic, and calcium-related genes expression analysis

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

Silicon nanoparticles (SiNPs) restore photosynthesis and essential oil content by upgrading enzymatic antioxidant metabolism in lemongrass (Cymbopogon flexuosus) under salt stress

Lemongrass (Cymbopogon flexuosus) has great relevance considering the substantial commercial potential of its essential oil. Nevertheless, the increasing soil salinity poses an imminent threat to lemongrass cultivation given its moderate salt-sensitivity. For this, we used silicon nanoparticles (SiNPs) to stimulate salt tolerance in lemongrass considering SiNPs special relevance to stress settings. Five foliar sprays of SiNPs 150 mg L^-1 were applied weekly to NaCl 160 and 240 mM-stressed plants. The data indicated that SiNPs minimised oxidative stress markers (lipid peroxidation, H₂O₂ content) while triggering a general activation of growth, photosynthetic performance, enzymatic antioxidant system including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and osmolyte proline (PRO). SiNPs amplified stomatal conductance and photosynthetic CO₂ assimilation rate by about 24% and 21% in NaCl 160 mM-stressed plants. Associated benefits contributed to pronounced plant phenotype over their stressed counterparts, as we found. Foliar SiNPs sprays assuaged plant height by 30% and 64%, dry weight by 31% and 59%, and leaf area by 31% and 50% under NaCl 160 and 240 mM concentrations, respectively. SiNPs relieved enzymatic antioxidants (SOD, CAT, POD) and osmolyte (PRO) in lemongrass plants stressed with NaCl 160 mM (9%, 11%, 9%, and 12%, respectively) and NaCl 240 mM (13%, 18%, 15%, and 23%, respectively). The same treatment supported the oil biosynthesis improving essential oil content by 22% and 44% during 160 and 240 mM salt stress, respectively. We found SiNPs can completely overcome NaCl 160 mM stress while significantly palliating NaCl 240 mM stress. Thus, we propose that SiNPs can be a useful biotechnological tool to palliate salinity stress in lemongrass and related crops.

Metabolomics and proteomics reveal the toxicological mechanisms of florfenicol stress on wheat (Triticum aestivum L.) seedlings

Although the ecological impacts of antibiotics have received attention worldwide, research on the toxicity of florfenicol is still limited. We conducted a metabolomic and proteomic study on wheat (Triticum aestivum L.) seedlings to reveal the toxicological mechanism of florfenicol. The growth of the wheat seedlings was found to be inhibited by florfenicol. Antioxidant enzyme activities (superoxide dismutase, peroxidase and catalase), malondialdehyde content and membrane permeability increased with increasing florfenicol concentration. The contents of chlorophyll and chlorophyll synthesis precursor substances (Proto IX, Mg-proto IX and Pchlide), photosynthetic and respiration rates, and chlorophyll fluorescence parameters decreased, indicating that photosynthesis was inhibited. The ultrastructure of chloroplasts was destroyed, as evidenced by the blurred membrane surface, irregular grana arrangement, irregular thylakoid lamella structure, and increased plastoglobuli number. Proteome analysis revealed that up-regulated proteins were highly involved in protein refolding, translation, oxidation-reduction, tricarboxylic acid cycle (TCA cycle), reactive oxygen species metabolic process, cellular oxidant detoxification, and response to oxidative stress. The down-regulated proteins were mainly enriched in photosynthesis-related pathways. In the metabolome analysis, the content of most of the metabolites in wheat leaves, such as carbohydrates and amino acids increased significantly (p < 0.05). Combined pathway analysis showed that florfenicol stress stimulated the TCA cycle pathway and downregulated the photosynthesis pathway.

The Disturbance of the Antioxidant System Results in Internal Blue Discoloration of Postharvest Cherry Radish (Raphanus sativus L. var. radculus pers) Roots

Internal blue discoloration in cherry radish (Raphanus sativus L. var. radculus pers) roots can appear after harvest. The antioxidant system and content of reactive oxygen species (ROS) will affect the blue discoloration. Currently, the reason for the blue discoloration is not yet clear. In order to reveal the mechanism of the blue discoloration of cherry radish, we selected the blue discolored cherry radish as the research object and the white cherry radish as the control. The difference in the antioxidant system between them were compared, including related enzymes and non-enzymatic antioxidants in this system. Meanwhile, the changes in the contents of 4-hydroxyglucobrassicin as a precursor substance and ROS were compared. The results showed that the activities of typical antioxidant enzymes decreased and the cycle of Glutathione peroxidase (GPX) and Ascorbic acid-Glutathione (ASA-GSH) was disturbed, leading to the reduction of antioxidant effect and the failure of timely and effective decomposition of superoxide anions (O₂^•-) and hydrogen peroxide (H₂O₂). In addition, the elevated level of O₂^•- and H₂O₂ led to the disorder of the antioxidant system, while the 4-hydroxybrassinoside was oxidized under the catalysis of peroxidase (POD) and eventually led to the internal blue discoloration in cherry radish. These results can provide a theoretical basis for solving the blue discoloration problem.

Diaporthe atlantica enhances tomato drought tolerance by improving photosynthesis, nutrient uptake and enzymatic antioxidant response

Functional symbiosis with fungal endophytes can help plants adapt to environmental stress. Diaporthe atlantica is one of the most abundant fungal taxa associated with roots of Festuca rubra subsp. pruinosa, a grass growing in sea cliffs. This study aimed to investigate the ability of a strain of this fungus to ameliorate the impact of drought stress on tomato plants. In a greenhouse experiment, tomato plants were inoculated with Diaporthe atlantica strain EB4 and exposed to two alternative water regimes: well-watered and drought stress. Several physiological and biochemical plant parameters were evaluated. Inoculation with Diaporthe promoted plant growth in both water treatments. A significant interactive effect of Diaporthe-inoculation and water-regime showed that symbiotic plants had higher photosynthetic capacity, water-use efficiency, nutrient uptake (N, P, K, Fe and Zn), and proline content under drought stress, but not under well-watered conditions. In addition, Diaporthe improved the enzymatic antioxidant response of plants under drought, through an induced mechanism, in which catalase activity was modulated and conferred protection against reactive oxygen species generation during stress. The results support that Diaporthe atlantica plays a positive role in the modulation of tomato plant responses to drought stress by combining various processes such as improving photosynthetic capacity, nutrient uptake, enzymatic antioxidant response and osmo-protectant accumulation. Thus, drought stress in tomato can be enhanced with symbiotic fungi.

Plant Growth Hormones and Nanomaterial Interface: Exploring the connection from development to defense

The global increase in nanotechnology applications has been unprecedented and has now moved into the area of agriculture and food production. Applications with promising potential in sustainable agriculture include nanobiosensors, nanofertilizers, nanopesticides, nano-mediated remediation strategies for contaminated soils and nanoscale strategies to increase crop production and protection. Given this, the impact of nanomaterials/nanoparticles (NPs) on plant species needs to be thoroughly evaluated as this represents a critical interface between the biosphere and the environment. Importantly, phytohormones represent a critical class of biomolecules to plant health and productivity; however, the impact of NPs on these molecules is poorly understood. In addition, phytohormones, and associated pathways, are widely explored in agriculture to influence several biological processes for the improvement of plant growth and productivity under natural as well as stressed conditions. However, the impact of exogenous applications of phytohormones on NP-treated plants has not been explored. The importance of hormone signaling and cross-talk with other metabolic systems makes these biomolecules ideal candidates for a thorough assessment of NP impacts on plant species. This article presents a critical evaluation of the existing yet limited literature available on NP-phytohormone interactions in plants. In addition, the developing strategy of nano-enabled precision delivery of phytohormones via nanocarriers will be explored. Finally, directions for future research and critical knowledge gaps will be identified for this important aspect of nano-enabled agriculture.

The Key Roles of ROS and RNS as a Signaling Molecule in Plant-Microbe Interactions

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play a pivotal role in the dynamic cell signaling systems in plants, even under biotic and abiotic stress conditions. Over the past two decades, various studies have endorsed the notion that these molecules can act as intracellular and intercellular signaling molecules at a very low concentration to control plant growth and development, symbiotic association, and defense mechanisms in response to biotic and abiotic stress conditions. However, the upsurge of ROS and RNS under stressful conditions can lead to cell damage, retarded growth, and delayed development of plants. As signaling molecules, ROS and RNS have gained great attention from plant scientists and have been studied under different developmental stages of plants. However, the role of RNS and RNS signaling in plant-microbe interactions is still unknown. Different organelles of plant cells contain the enzymes necessary for the formation of ROS and RNS as well as their scavengers, and the spatial and temporal positions of these enzymes determine the signaling pathways. In the present review, we aimed to report the production of ROS and RNS, their role as signaling molecules during plant-microbe interactions, and the antioxidant system as a balancing system in the synthesis and elimination of these species.

5-Aminolevulinic Acid Induces Chromium [Cr(VI)] Tolerance in Tomatoes by Alleviating Oxidative Damage and Protecting Photosystem II: A Mechanistic Approach

Chromium [Cr(VI)] pollution is a major environmental risk, reducing crop yields. 5-Aminolevunic acid (5-ALA) considerably improves plant abiotic stress tolerance by inducing hydrogen peroxide (H₂O₂) and nitric oxide (NO) signalling. Our investigation aimed to uncover the mechanism of tomato tolerance to Cr(VI) toxicity through the foliar application of 5-ALA for three days, fifteen days before Cr treatment. Chromium alone decreased plant biomass and photosynthetic pigments, but increased oxidative stress markers, i.e., H₂O₂ and lipid peroxidation (as MDA equivalent). Electrolyte leakage (EL), NO, nitrate reductase (NR), phytochelatins (PCs), glutathione (GSH), and enzymatic and non-enzymatic antioxidants were also increased. Foliar application of 5-ALA before Cr treatment improved plant growth and photosynthetic pigments, diminished H₂O₂, MDA content, and EL, and resulted in additional enhancements of enzymatic and non-enzymatic antioxidants, NR activity, and NO synthesis. In Cr-treated tomato seedlings, 5-ALA enhanced GSH and PCs, which modulated Cr sequestration to make it nontoxic. 5-ALA-induced Cr tolerance was further enhanced by sodium nitroprusside (SNP), a NO donor. When sodium tungstate (ST), a NR inhibitor, was supplied together with 5-ALA to Cr-treated plants, it eliminated the beneficial effects of 5-ALA by decreasing NR activity and NO synthesis, while the addition of SNP inverted the adverse effects of ST. We conclude that the mechanism by which 5-ALA induced Cr tolerance in tomato seedlings is mediated by NR-generated NO. Thus, NR and NO are twin players, reducing Cr toxicity in tomato plants via antioxidant signalling cascades.

The combination of salt and drought benefits selective ion absorption and nutrient use efficiency of halophyte Panicum antidotale

Soil salinity and water deficit often occur concurrently, but understanding their combined effects on plants' ion regulation is limited. With aim to identify if introducing drought with salinity alleviates salt stress's ionic effects, Panicum antidotale - a halophytic grass- was grown in the presence of single and combined stressors, i.e., drought and salt (low and high). Regulation of cations and anions along with the antioxidant capacity and modifications in leaf anatomy were investigated. Results showed a combination of low salt and drought minimally affected plant (dry) mass by improving the selective ions absorption and nutrient use efficiencies. The lowest ratio for efficiency of photosystem II and carbon assimilation (ΦPSII/ΦCO₂) suggested less generation of reactive oxygen species, which were probably detoxified with constitutively performing antioxidant enzymes. In contrast, the combination of high salinity and drought escalated the adverse effects caused due to individual stressors. The selective ion absorption increased, but the non-selective ions transport caused an ionic imbalance indicating the highest ratio of Na⁺/K⁺. Although the area of mesophyll increased, a reduction in epidermis (cell number and area) predicted a mechanical injury prone to water loss in these plants. The compromised activity of antioxidant enzymes also suggested treatment-induced oxidative damage. Yet, the synergistic interaction between high salinity and drought was not detrimental to the survival of P. antidotale. Therefore, we suggest planting this grass in habitats with harsh environmental conditions to meet the increasing fodder demands without compromising agricultural lands' productivity.

Multiple pathways mediate chloroplast singlet oxygen stress signaling

Chloroplast singlet oxygen initiates multiple pathways to control chloroplast degradation, cell death, and nuclear gene expression. Chloroplasts can respond to stress and changes in the environment by producing reactive oxygen species (ROS). Aside from being cytotoxic, ROS also have signaling capabilities. For example, the ROS singlet oxygen (¹O₂) can initiate nuclear gene expression, chloroplast degradation, and cell death. To unveil the signaling mechanisms involved, researchers have used several ¹O₂-producing Arabidopsis thaliana mutants as genetic model systems, including plastid ferrochelatase two (fc2), fluorescent in blue light (flu), chlorina 1 (ch1), and accelerated cell death 2 (acd2). Here, we compare these ¹O₂-producing mutants to elucidate if they utilize one or more signaling pathways to control cell death and nuclear gene expression. Using publicly available transcriptomic data, we demonstrate fc2, flu, and ch1 share a core response to ¹O₂ accumulation, but maintain unique responses, potentially tailored to respond to their specific stresses. Subsequently, we used a genetic approach to determine if these mutants share ¹O₂ signaling pathways by testing the ability of genetic suppressors of one ¹O₂ producing mutant to suppress signaling in a different ¹O₂ producing mutant. Our genetic analyses revealed at least two different chloroplast ¹O₂ signaling pathways control cellular degradation: one specific to the flu mutant and one shared by fc2, ch1, and acd2 mutants, but with life-stage-specific (seedling vs. adult) features. Overall, this work reveals chloroplast stress signaling involving ¹O₂ is complex and may allow cells to finely tune their physiology to environmental inputs.

Moving beyond standard toxicological metrics: The effect of diclofenac on planktonic host-parasite interactions

Pharmaceuticals are increasingly released into surface waters and therefore ubiquitous in aquatic systems. While pharmaceuticals are known to influence species interactions, their effect on host-parasite interactions is still underexplored despite potential ecosystem-level consequences. Here, we ask whether diclofenac, a widely used non-steroid anti-inflammatory drug, affects the interaction between a phytoplankton host (Staurastrum sp.; green alga) and its obligate fungal parasite (Staurastromyces oculus; chytrid fungus). We hypothesized that the effect of increasing diclofenac concentration on the host-parasite system depends on parasite exposure. We assessed acute and chronic effects of a wide range of diclofenac concentrations (0-150 mg/L) on host and parasite performance using a replicated long gradient design in batch cultures. Overall system response summarizing parameters related to all biotic components in an experimental unit i.e., number of bacteria and phytoplankton host cells along with photosynthetic yield (a measure of algal cell fitness), depended on diclofenac concentration and presence/absence of parasite. While host standing biomass decreased at diclofenac concentrations >10 mg/L in non-parasite-exposed treatments, it increased at ≥10 mg/L in parasite-exposed treatments since losses due to infection declined. During acute phase (0-48 h), diclofenac concentrations <0.1 mg/L had no effect on host net-production neither in parasite-exposed nor non-parasite-exposed treatments, but parasite infection ceased at 10 mg/L. During chronic phase (0-216 h), host net-production declined only at concentrations >10 mg/L in non-parasite-exposed cultures, while it was overall close to zero in parasite-exposed cultures. Our results suggest that chytrid parasites are more sensitive to diclofenac than their host, allowing a window of opportunity for growth of phytoplankton hosts, despite exposure to a parasite. Our work provides a first understanding about effects of a pharmaceutical on a host-parasite interaction beyond those defined by standard toxicological metrics.

Effects of elevated CO2 concentration and temperature on the mixed-culture grown wild mustard (Sinapis arvensis L.) response to auxin herbicide

Recently, there has been growing concern over the potential impact of CO₂ concentration and temperature on herbicide efficacy. The aim of the study was to examine the influence of single elevated CO₂ (400 vs. 800 ppm) and elevated CO₂ in combination with temperature (21 °C vs. 25 °C) on the effects of auxin herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) (0.5-2 × field recommended rate) to wild mustard (Sinapis arvensis L.) grown in mixed-culture with spring barley (Hordeum vulgare L.). MCPA had a detrimental effect on aboveground and belowground biomass, content of chlorophylls, enzymatic and non-enzymatic antioxidants and induced oxidative stress. The significant decline in photosynthetic rate, stomatal conductance and transpiration with MCPA dose was detected. Elevated CO₂ reinforced MCPA efficacy on S. arvensis: sharper decline in biomass, photosynthetic rate and antioxidant enzymes and more pronounced lipid peroxidation were detected. Under elevated CO₂ and temperature, MCPA efficacy to control S. arvensis dropped due to herbicide dilution because of increased root:shoot ratio, higher activity of antioxidants and less pronounced oxidative damage. Reinforced MCPA impact on weeds under elevated CO₂ resulted in higher H. vulgare biomass, while decreased MCPA efficacy under elevated CO₂ and temperature reduced H. vulgare biomass.

Trx CDSP32-overexpressing tobacco plants improves cadmium tolerance by modulating antioxidant mechanism

The effects of overexpression of the thioredoxin-like protein CDSP32 (Trx CDSP32) on reactive oxygen species (ROS) metabolism in tobacco leaves exposed to cadmium (Cd) were studied by combining physiological measures and proteomics technology. Thus, the number of differentially expressed proteins (DEPs) in plants overexpressing the Trx CDSP32 gene in tobacco (OE) was observed to be evidently lower than that in wild-type (WT) tobacco under Cd exposure, especially the number of down-regulated DEPs. Cd exposure induced disordered ROS metabolism in tobacco leaves. Although Cd exposure inhibited the activities of superoxide dismutase (SOD), catalase (CAT), and l-ascorbate peroxidase (APX) and the expression of proteins related to the thioredoxin-peroxiredoxin (Trx-Prx) pathway, the increase in the activities of peroxidase (POD), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), and glutathione S-transferase (GST) and their protein expression levels played an important role in the physiological response to Cd exposure. Notably, Trx CDSP32 was observed to alleviate the decrease in the expression and activities of SOD and CAT caused by Cd exposure and enhance the function of POD. Trx CDSP32 was observed to increase the H₂O₂ scavenging capacity of the ascorbic acid-glutathione (AsA-GSH) cycle and Trx-Prx pathway under Cd exposure, and it can especially regulate 2-Cys peroxiredoxin (2-Cys Prx) protein expression and thioredoxin peroxidase (TPX) activity. Thus, overexpression of the Trx CDSP32 gene can alleviate the oxidative damage that occurs in tobacco leaves under Cd exposure by modulating antioxidant defense systems.

Pyruvic acid as attenuator of water deficit in cotton plants varying the phenological stage

The lack of water during crop growth causes damage to any production system, especially when it occurs during the initial establishment or beginning of the reproductive stage. Although cotton can be properly managed in regions with water limitation, its yield is affected at different levels according to the genetics of the cultivar adopted. Exogenous application of some organic components has shown a stress-mitigating effect and can be a valuable procedure to enhance the yield of water stress-sensitive cultivars. The objective of this work was to evaluate the benefits of exogenous application of pyruvic acid (100 µM) in cotton plants under water deficit varying the phenological stage of the crop. The experiment was conducted in a greenhouse, where the plants were grown in pots and subjected to seven days of water suspension, initiated individually in stages V2 and B1. Each pot contained two plants. The treatments adopted were: T1 - control, T2 - water suppression; and T3 - water suppression + pyruvate application. The design was randomized blocks in a factorial scheme (3 × 3) with three replicates. The reductions in gas exchange and growth of the cultivars BRS Seridó, CNPA 7MH and FM 966 were more significant in the reproductive stage, especially for FM 966, which was more sensitive. Pyruvate application reduced the effects of water suppression on boll production by 31% in BRS Seridó and 34% in CNPA 7MH and FM 966.

Effect of ofloxacin levels on growth, photosynthesis and chlorophyll fluorescence kinetics in tomato

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

High light-induced changes in thylakoid supercomplexes organization from cyclic electron transport mutants of Chlamydomonas reinhardtii

The localization of carotenoids and macromolecular organization of thylakoid supercomplexes have not been reported yet in Chlamydomonas reinhardtii WT and cyclic electron transport mutants (pgrl1 and pgr5) under high light. Here, the various pigments, protein composition, and pigment-protein interactions were analyzed from the cells, thylakoids, and sucrose density gradient (SDG) fractions. Also, the supercomplexes of thylakoids were separated from BN-PAGE and SDG. The abundance of light-harvesting complex (LHC) II trimer complexes and pigment-pigment interaction were changed slightly under high light, shown by circular dichroism. However, a drastic change was seen in photosystem (PS)I-LHCI complexes than PSII complexes, especially in pgrl1 and pgr5. The lutein and β-carotene increased under high light in LHCII trimers compared to other supercomplexes, indicating that these pigments protected the LHCII trimers against high light. However, the presence of xanthophylls, lutein, and β-carotene was less in PSI-LHCI, indicating that pigment-protein complexes altered in high light. Even the real-time PCR data shows that the pgr5 mutant does not accumulate zeaxanthin dependent genes under high light, which shows that violaxanthin is not converting into zeaxanthin under high light. Also, the protein data confirms that the LHCSR3 expression is absent in pgr5, however it is presented in LHCII trimer in WT and pgrl1. Interestingly, some of the core proteins were aggregated in pgr5, which led to change in photosynthesis efficiency in high light.

Cold acclimation alleviates cold stress-induced PSII inhibition and oxidative damage in tobacco leaves

This study aimed to explore how cold acclimation (CA) modulates cold stress in tobacco leaves and reveal the relationship between CA and cold stress resistance, and the mechanism of CA-induced plant resistance to cold stress. This study examined the effects of CA treatment (at 8-10℃ for 2 d) on the cold tolerance of tobacco leaves under 4°C cold stress treatment using seedlings without CA treatment as the control (NA). In both CA and NA leaves, cold stress treatment resulted in a decrease in maximum photochemical efficiency of PSII (Fv/Fm), increase in relative variable fluorescence (VJ) at 2 ms on the standardized OJIP curve, inhibition of PSII activity, and impairment of electron transfer on the acceptor side. Besides increasing the malondialdehyde (MDA) content and electrolyte leakage rate, the cold stress exacerbated the degree of membrane peroxidation. The CA treatment also induced the accumulation of reactive oxygen species (ROS), including superoxide anion (O2·-) and H2O2, and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbic acid peroxidase (APX). The CA treatment also enhanced the accumulation of soluble sugar (SS) and soluble protein (SP), cyclic electron flow (CEF), and the proportion of regulatory energy dissipation Y(NPQ). Moreover, CA+ cold stress treatment significantly reduced CEF and Y(NPQ) in tobacco leaves than under NA+ cold stress treatment, thus significantly alleviating the degree of PSII photoinhibition. In conclusion, CA treatment significantly alleviated PSII photoinhibition and oxidative damage in tobacco leaves under cold stress treatment. Improvement in cold resistance of tobacco leaves is associated with the induction of antioxidant enzyme activity, accumulation of osmoregulation substances, and initiation of photoprotective mechanisms.

CO2 Levels Modulate Carbon Utilization, Energy Levels and Inositol Polyphosphate Profile in Chlorella

Microalgae have a growing recognition of generating biomass and capturing carbon in the form of CO₂. The genus Chlorella has especially attracted scientists' attention due to its versatility in algal mass cultivation systems and its potential in mitigating CO₂. However, some aspects of how these green microorganisms respond to increasing concentrations of CO₂ remain unclear. In this work, we analyzed Chlorella sorokiniana and Chlorella vulgaris cells under low and high CO₂ levels. We monitored different processes related to carbon flux from photosynthetic capacity to carbon sinks. Our data indicate that high concentration of CO₂ favors growth and photosynthetic capacity of the two Chlorella strains. Different metabolites related to the tricarboxylic acid cycle and ATP levels also increased under high CO₂ concentrations in Chlorella sorokiniana, reaching up to two-fold compared to low CO₂ conditions. The signaling molecules, inositol polyphosphates, that regulate photosynthetic capacity in green microalgae were also affected by the CO₂ levels, showing a deep profile modification of the inositol polyphosphates that over-accumulated by up to 50% in high CO₂ versus low CO₂ conditions. InsP₄ and InsP₆ increased 3- and 0.8-fold, respectively, in Chlorella sorokiniana after being subjected to 5% CO₂ condition. These data indicate that the availability of CO₂ could control carbon flux from photosynthesis to carbon storage and impact cell signaling integration and energy levels in these green cells. The presented results support the importance of further investigating the connections between carbon assimilation and cell signaling by polyphosphate inositols in microalgae to optimize their biotechnological applications.

Relevance of the Exocyst in Arabidopsis exo70e2 Mutant for Cellular Homeostasis under Stress

Plants must adapt to cope with adverse environmental conditions that affect their growth and development. To overcome these constraints, they can alter their developmental patterns by modulating cellular processes and activating stress-responsive signals. Alongside the activation of the antioxidant (AOX) system, a high number of genes are expressed, and proteins must be distributed to the correct locations within the cell. The endomembrane system and associated vesicles thus play an important role. Several pathways have been associated with adverse environmental conditions, which is the case for the exocyst-positive organelle-EXPO. The present work, using Arabidopsis mutants with T-DNA insertions in the gene EXO70, essential for EXPO vesicles formation, was designed to characterise the anatomical (morphology and root length), biochemical (quantification of stress markers and antioxidant system components), and molecular responses (gene expression) to abiotic stresses (saline, drought, oxidative, and metal-induced toxicity). The results obtained showed that mutant plants behave differently from the wild type (WT) plants. Therefore, in the exo70 mutant, morphological changes were more noticeable in plants under stress, and the non-enzymatic component of the antioxidant system was activated, with no alterations to the enzymatic component. Furthermore, other defence strategies, such as autophagy, did not show important changes. These results confirmed the EXPO as an important structure for tolerance/adaptation to stress.

Structure-function correlations and system dynamics in oxygenic photosynthesis: classical perspectives and murburn precepts

HIGHLIGHTS

Contemporary beliefs on oxygenic photosynthesis are critiqued.Murburn model is suggested as an alternative explanation.In the new model, diffusible reactive species are the main protagonists.All pigments are deemed photo-redox active in the new stochastic mechanism.NADPH synthesis occurs via simple electron transfers, not via elaborate ETC.Oxygenesis is delocalized and not just centered at Mn-Complex.Energetics of murburn proposal for photophosphorylation is provided.The proposal ushers in a paradigm shift in photosynthesis research.

Morphoanatomical, Physiological, and Biochemical Indicators in Lactuca sativa L. Germination and Growth in Response to Fluoride

Fluoride is one of the main phytotoxic environmental pollutants, and high concentrations (10-30 mg L^-1) are commonly detected in surface and groundwater. Little, however, is known about the effects of this pollutant on crops that require irrigation during their development, which, in addition to phytotoxicity, may cause negative human health effects. Thus, the aim of this study was to characterize the effects of potassium fluoride (KF) on the germination of lettuce seeds and identify the physiological and anatomical markers of this pollutant's action on plants exposed to it during growth. Initially, lettuce seeds were sown in gerboxes and soaked in solutions containing 0 mg L^-1, 10 mg L^-1, 20 mg L^-1, and 30 mg L^-1 KF. Plants grown in a greenhouse were treated daily with KF irrigation at the same KF concentrations for 40 days. KF exposure reduced the germination rate and germination speed index of lettuce seeds at 20 mg L^-1 and 30 mg L^-1, resulting in compromised root development at the highest KF concentration. Lettuce plants displayed a slight photosynthesis reduction and a significant photochemical efficiency decrease after exposures to all KF concentrations. Lower chlorophyll contents and nitrogen balance indices were observed in plants exposed to 30 mg L^-1 KF. On the other hand, increases in phenolic compounds and malondialdehyde were noted with increasing KF concentrations. Lettuce plants can, therefore, accumulate fluoride in leaves when irrigated with KF-rich water. The investigated physiological and biochemical variables were proven to be adequate fluoride action biomarkers in lettuce plants and may become an important tool in the study of olericulture contaminants.

The IbPYL8-IbbHLH66-IbbHLH118 complex mediates the abscisic acid-dependent drought response in sweet potato

Drought limits crop development and yields. bHLH (basic helix-loop-helix) transcription factors play critical roles in regulating the drought response in many plants, but their roles in this process in sweet potato are unknown. Here, we report that two bHLH proteins, IbbHLH118 and IbbHLH66, play opposite roles in the ABA-mediated drought response in sweet potato. ABA treatment repressed IbbHLH118 expression but induced IbbHLH66 expression in the drought-tolerant sweet potato line Xushu55-2. Overexpressing IbbHLH118 reduced drought tolerance, whereas overexpressing IbbHLH66 enhanced drought tolerance, in sweet potato. IbbHLH118 directly binds to the E-boxes in the promoters of ABA-insensitive 5 (IbABI5), ABA-responsive element binding factor 2 (IbABF2) and tonoplast intrinsic protein 1 (IbTIP1) to suppress their transcription. IbbHLH118 forms homodimers with itself or heterodimers with IbbHLH66. Both of the IbbHLHs interact with the ABA receptor IbPYL8. ABA accumulates under drought stress, promoting the formation of the IbPYL8-IbbHLH66-IbbHLH118 complex. This complex interferes with IbbHLH118's repression of ABA-responsive genes, thereby activating ABA responses and enhancing drought tolerance. These findings shed light on the role of the IbPYL8-IbbHLH66-IbbHLH118 complex in the ABA-dependent drought response of sweet potato and identify candidate genes for developing elite crop varieties with enhanced drought tolerance.

Photoacclimation of photosystem II photochemistry induced by rose Bengal and methyl viologen in Nannochloropsis oceanica

The photosynthetic apparatus is a major reactive oxygen species (ROS) proliferator, especially in high-light environments. The role of ROS in photoinhibition and photoacclimation mechanisms has been extensively explored, primarily in model plant species. However, little work has been performed on the topic in non-Archaeplastida organisms, such as the model heterokont species Nannochloropsis oceanica. To investigate the photoacclimation and damaging impact of singlet oxygen and superoxide anions on the photosynthetic apparatus of N. oceanica, we subjected cells to two doses of methyl viologen and rose bengal. Significant findings: Rose bengal (a singlet-oxygen photosensitizer) induced changes to the photosynthetic apparatus and PSII photochemistry mirroring high-light-acclimated cells, suggesting that singlet-oxygen signaling plays a role in the high-light acclimation of PSII. We further suggest that this singlet-oxygen pathway is mediated outside the plastid, given that rose bengal caused no detectable damage to the photosynthetic apparatus. Methyl viologen (a superoxide-anion sensitizer) induced an enhanced non-photochemical quenching response, similar to what occurs in high-light-acclimated cells. We propose that superoxide anions produced inside the plastid help regulate the high-light acclimation of photoprotective pathways.

Exogenous nano-silicon application improves ion homeostasis, osmolyte accumulation and palliates oxidative stress in Lens culinaris under NaCl stress

Lentil is one of the highly nutritious legumes but is highly susceptible to salinity stress. Silicon has been known to reduce the effect of various environmental stresses including salinity. Moreover, silicon when applied in its nano-form is expected to augment the beneficial attributes of silicon. However, very little is known regarding the prospect of nano-silicon (nSi) application for alleviating the effect of salinity stress in non-silicified plants like lentil. In this study, the primary objective was to evaluate the efficacy of nSi in the alleviation of NaCl stress during germination and early vegetative stages. In this context, different concentrations of nSi (0, 1, 5, 10 g L-1) was applied along with four different concentrations of NaCl (0, 100, 200, 300 mM). The results indicated the uptake of nSi which was confirmed by the better accumulation of silica in the plant tissues. Most importantly, the enhanced accumulation of silica increased the K+/Na+ ratio of the NaCl-stressed seedlings. Moreover, nSi efficiently improved germination, growth, photosynthetic pigments, and osmotic balance. On the other hand, the relatively reduced activities of antioxidative enzymes were surmounted by the higher activity of non-enzymatic antioxidants which mainly scavenged the increased ROS. Reduced ROS accumulation in return ensured better membrane integrity and reduced electrolyte leakage up on nSi application. Therefore, it can be concluded that the application of nSi (more specifically at 10 g L-1) facilitated the uptake of silica and improved the K+/Na+ ratio to reclaim the growth and physiological status of NaCl-stressed seedlings.