Understanding oxidative stress and antioxidant functions to enhance photosynthesis

Effect of temperature on the physiology and phytoremediation capacity of Spirodela polyrhiza exposed to atrazine and S-metolachlor

Environmental toxicity of pesticides to aquatic plants can vary with temperature, as temperature affects plant metabolic processes. We exposed the globally distributed duckweed Spirodela polyrhiza to environmentally relevant concentrations (40 µg/L) of atrazine and S-metolachlor at temperatures typical of surface freshwater in temperate zones (10, 15, and 21 °C). Our objective was to assess the effects of low temperatures and herbicide concentration, and their interactions, on growth, photosynthesis, pigments, antioxidant enzymes, and phytoremediation capacity. Lower temperatures (10 °C) intensified the adverse effects of both herbicides on the quantum yield of photosystem II in S. polyrhiza, with photosynthesis being a more sensitive endpoint than biomass growth rate. Both in the control and herbicide treatments, plants exposed to 10 °C exhibited lower concentrations of photosynthetic pigments (chlorophylls and carotenoids) and reduced ascorbate peroxidase activity, which may have contributed to the intensified negative effects on photosynthesis at this temperature. The removal of S-metolachlor was lower at 10 and 15 °C (3-8 %) compared to 21 °C (17 %), while no difference was observed between the three tested temperatures for atrazine (2-8 %). Our findings suggest that conducting pesticide toxicity tests at around 25 °C may underestimate the contaminants' inhibitory effects on aquatic plants during colder seasons and in temperate regions. Additionally, lower temperatures pose a challenge to the effectiveness of atrazine and S-metolachlor phytoremediation in aquatic environments.

Mechanisms of plant acclimation to multiple abiotic stresses

Plants frequently encounter a range of abiotic stresses and their combinations. Even though stresses rarely occur in isolation, research on plant stress resilience typically focuses on single environmental stressors. Plant responses to abiotic stress combinations are often distinct from corresponding individual stresses. Factors determining the outcomes of combined stresses are complex and multifaceted. In this review, we summarize advancements in our understanding of the mechanisms underlying plant responses to co-occurring (combined and sequential) abiotic stresses, focusing on morphological, physiological, developmental, and molecular aspects. Comprehensive understanding of plant acclimation, including the signaling and response mechanisms to combined and individual stresses, can contribute to the development of strategies for enhancing plant resilience in dynamic environments.

NBS1 from Physcomitrium patens confers resistance against oxidative stress through the BRCA1 C-terminus (BRCT) domain, independent of the MRE11 interaction

The Nijmegen breakage syndrome 1 (NBS1) protein is a core member of the MRE11-RAD50-NBS1 (MRN) complex and is known to function as a DNA damage sensor within the plant DNA damage response (DDR) pathway. We previously reported that NBS1 from Physcomitrium patens (PpNBS1) also plays a pivotal role in the defense against oxidative damage by reducing the level of cellular reactive oxygen species (ROS). Our study demonstrated that overexpression of PpNBS1 induces the expression of antioxidant genes involved in ROS scavenging in transgenic tobacco plants, leading to reduced accumulation of hydrogen peroxide (H2O2) and superoxide (O2•-). In this study, we generated N-terminal and C-terminal truncation mutants of the protein to selectively eliminate specific functional domains to characterize the role of PpNBS1 in cellular ROS detoxification. Transgenic tobacco plants overexpressing PpNBS1 truncation mutants were generated and evaluated for their oxidative stress tolerance. PpNBS1 mutant plants lacking the BRCA1 C-terminal (BRCT) domain exhibited compromised stress tolerance. Our findings underscore the importance of the N-terminal BRCT domain of PpNBS1 in oxidative stress tolerance and provide evidence that the BRCT domain is crucial for the increased expression of ROS-scavenging enzymes. Furthermore, our findings confirm that the C-terminal region of PpNBS1 is critical for its binding with PpMRE11 (Meiotic recombination 11). Nevertheless, transgenic plants expressing the PpNBS1 mutant lacking the NBS_C terminal domain presented resistance to oxidative stress comparable to that of PpNBS1-transgenic plants. Overall, we deduce that PpNBS1 protects against oxidative stress via the BRCT domain, regardless of its interaction with MRE11.

Root-applied brassinosteroid and salicylic acid enhance thermotolerance and fruit quality in heat-stressed 'Kyoho' grapevines

Introduction

The increasingly severe global greenhouse effect has become an irreversible trend, significantly impacting viticulture regions through heat stress during various grape growth stages, especially under protected cultivation conditions where high temperatures frequently occur. Therefore, studying the impact of heat stress on grapevine growth and fruit quality across the entire growth and development period, along with effective mitigation measures, is crucial.

Methods

In this study, three-year-old 'Kyoho' grapevines were used as experimental materials, with four treatment groups: a control group, a hightemperature group (heat stress, HT), a high-temperature + brassinolide group (BR), and a high-temperature + salicylic acid group (SA). During the flowering, young berry swelling, and veraison stages, BR and SA were applied via nutrient solutions every seven days.

Results

The results demonstrated that BR restored the maximum photosynthetic rate (Amax) to 96.14% of CK by the 18th day of flowering, significantly outperforming SA's recovery rate of 86.64%. Both treatments maintained light saturation points (1200 μmol•m⁻²•s⁻¹) and CO2 saturation thresholds equivalent to CK. The decline in PSII photochemical efficiency (Fv/Fm) was reduced from 18% in HT to 5-8% in BR/SA-treated groups, with BR showing minimal deviation (2.3%) from CK during veraison, effectively mitigating PSII photoinhibition caused by heat stress. Furthermore, both treatments reduced leaf malondialdehyde (MDA) content, minimizing membrane lipid peroxidation, while increasing soluble protein (SP) content to protect leaves. Under heat stress, BR notably improved the fruit set rate by 22.67% compared to HT (SA: 13%), promoted berry expansion, and enhanced the accumulation of sugars and anthocyanins in the fruit skin, with SA showing similar, though slightly less pronounced, effects.

Discussion

These findings provide valuable theoretical insights into the use of exogenous hormones in root nutrient solutions as a strategy to mitigate the adverse effects of heat stress in grape production.

The 14-3-3 gene AaGRF1 positively regulates cold tolerance in kiwifruit

Low temperatures severely threaten the growth and development of kiwifruit. Research has demonstrated that proteins belonging to the 14-3-3 family play a pivotal regulatory function in the ability of plants to resist stress. However, this specific roles of the genes in kiwifruit cold tolerance remain unclear. It had been identified that β-amylase gene, AaBAM3.1, exhibits a positive regulatory effect on kiwifruit's tolerance to low temperature. In our research, we obtained the Actinidia arguta 14-3-3 gene general regulatory factor 1 (AaGRF1) from yeast one-hybrid (Y1H) screening library of the AaBAM3.1 promoter; the expression level of AaGRF1 was enhanced by low-temperature stress. Subcellular localization, Y1H and dual-LUC assay indicated that the AaGRF1 protein resides within the nucleus and possesses the ability to interact with the AaBAM3.1 promoter. Moreover, we also studied the role of AaGRF1 gene in cold resistance of kiwifruit. When AaGRF1 was overexpressed in kiwifruit, the transgenic plants exhibited enhanced cold tolerance. The level of antioxidants and soluble sugars in these plants were elevated compared to wild-type (WT) lines. RNA-seq of the transgenic and WT lines revealed that AaGRF1 might interact with genes in the 'ascorbate-glutathione' and 'starch and sucrose' pathways, thereby enhancing the cold resistance of kiwifruit. In summary, we hypothesize that the 14-3-3 gene AaGRF1 may positively modulate the cold resistance in kiwifruit by accumulating more antioxidants and soluble sugars.

Microtubule-mediated defence reaction of grapevine to Neofusicoccum parvum via the transcription factor VrWRKY22 promoting the kinesin-like protein VrKIN10C

Grapevine Trunk Diseases (GTDs) are among the most destructive diseases in viticulture due to global climate change. Some causal agents like Neofusicoccum parvum can be latent endophytic and become pathogenic under abiotic stress. Microtubules (MTs) have been found to play a role in mediating the pathogen-related signaling in grapevine. In this study, a novel transcription factor VrWRKY22 was identified and cloned from the native American grapevine Vitis rupestris. Leaves of the table grape variety 'Kyoho' (V. vinifera × V. labrusca L.) overexpressing VrWRKY22 showed less necroses after N. parvum Bt-67 inoculation and activated signaling pathways. VrWRKY22 interacted with VrMPK3 and then bounded to the TTGACC motif in the promoter of VrKIN10C, which was confirmed by Y2H and Y1H assays. Since VrKIN10C is one of the important kinesin-like proteins associated with MTs, a grapevine MT marker line overexpressing VrWRKY22 was generated to test the responses of grapevine cells to N. parvum Bt-67. An increased number of prompt movement proteins can be traced within the peri-nuclear MTs and along the cortical MTs. The skewness and thickness of both central and cortical MTs were significantly increased. Moreover, a prominent (resulting from both the number and the rate) accumulation of speckles appeared in the nucleus and cortical MTs. A significant reduction in cell mortality and a stronger antioxidant capacity were detected. This study demonstrates that VrWRKY22 plays positive roles during N. parvum Bt-67 invasion by rapidly increasing the concentration and dynamics of MTs in the peri-nuclear and cortical regions via VrKIN10, and will facilitate the interpretation of the results of further GTD mitigation studies.

Grain lysine enrichment and improved stress tolerance in rice through protein engineering

Amino acids are a major source of nourishment for people living in regions where rice is a staple food. However, rice grain is deficient in essential amino acids including lysine. The activity of the enzyme dihydrodipicolinate synthase (DHDPS) is crucial for lysine production in higher plants, but it is tightly regulated through feedback inhibition by its end product, lysine, leading to limited activity in the grain and resulting in low lysine accumulation. We identified lysine binding sites in the DHDPS enzyme and introduced key mutations to make DHDPS lysine feedback insensitive. Using in vivo analysis and functional complementation assays, we confirmed that protein engineering of the DHDPS renders it insensitive to lysine. Expression of mutated DHDPS resulted in 29% higher lysine and 15% higher protein accumulation in rice grains than in the wild type. Importantly, the lysine content in transgenic grains was maintained in cooked rice. The transgenic plants also exhibited enhanced stress tolerance along with higher antioxidant levels, improved photosynthesis, and higher grain yield compared to wild-type plants. We have shown that protein engineering of DHDPS in rice can lead to accumulation of lysine in grains and impart abiotic stress tolerance. This approach could improve health in regions with nutrient deficiencies and environmental stressors that challenge food production and human health.

Molecular mechanisms of nitric oxide regulating high photosynthetic performance of wheat plants in waterlogging at flowering

Nitric oxide (NO) positively contributes to maintaining a high photosynthetic rate in waterlogged-wheat plants by maintaining high stomatal conductance (gs), mesophyll conductance (gm), and electron transport rates in PSII (J). However, the molecular mechanisms underlying the synergistic regulation of photosynthetic characteristics during wheat waterlogging remain unclear. Pot experiments were conducted with two cultivars: Yangmai15 (YM15: high waterlogging-tolerance capacity) and Yangmai24 (YM24: conventional waterlogging-tolerance capacity). The 2 cm waterlogging depth treatment (WL), exogenous spraying of NO every two days in the WL treatment (WLsnp), and suitable soil water content treatment (CK) were established during the flowering stage for eight consecutive days. RNA-seq, weighted gene co-expression network analysis (WGCAN), and protein interaction analysis were performed on the 8th day to screen key genes that maintain high photosynthetic performance in waterlogged-wheat plants. The results indicated that cultivar YM24 and YM15 contained 10411 and 10582 differentially expressed genes (DEGs), respectively. The WL treatment had obviously higher DEGs than the WLsnp treatment compared to the CK treatment. Based on the WGCAN method, the DEGs were clustered into eight modules and correlated significantly with the four photosynthetic parameters mentioned above (P < 0.05). Only the DEGs in the ivory module (571) enriched the photosynthetic pathways among the eight modules. In the ivory module, 10 hub genes, including TaB1274F11.29-1, TaT6H20.190, TaOSNPB_100100300, TaLHCB, TaPSAG, TaCAP10B, TaFAD7A-1, TaCAB3C, TaT27G7, and TaF24G24.140, were screened using the co-expression network method because the genes exhibited similar variation trends with gs, gm, or J across the three water treatments and both cultivars. TaLHCB and TaCAP10B exhibited significant linear relationships with the three parameters of gs, gm, and J (P < 0.05). Consequently, TaLHCB and TaCAP10B genes are defined as waterlogging-resistance genes due to the synergistic regulation of photosynthetic characteristics in waterlogging. Both genes were significantly down-regulated in the WL treatment compared to CK treatment in both cultivars. However, there was no significant difference between WLsnp and CK treatments for the genes in the cultivar YM15. These results suggest that the positive effects of spraying NO with high waterlogging resistance capacities are linked to maintaining high expression levels of key genes and obtaining high photosynthetic characteristics during waterlogging, particularly for cultivars with high waterlogging resistance.

Cytotoxicity of single and binary mixtures of copper and silica nanoparticles exposed to Nitzschia closterium f. minutissima

A large number of nanoparticles are produced and enter the aquatic environment, where they interact with each other, posing a potential threat to aquatic organisms. The toxicity of two types of nanoparticles (nCu and nSiO2) on Nitzschia closterium f. minutissima (N. closterium f. minutissima) was investigated in this study by examining changes in microalgal cell density, instantaneous fluorescence rate (Ft), and a range of antioxidant parameters in the cells. It was found that both nCu and nSiO2 showed time- and concentration-dependent toxic effects on N. closterium f. minutissima. nSiO2 could promote microalgae growth at low concentrations by providing Si, an essential element for the synthesis of siliceous shells. As the exposure time increased, both the growth and photosynthetic efficiency of the microalgae were inhibited. Nanoparticles also produced oxidative stress and caused lipid peroxidation in the microalgae. In the meantime, SOD and CAT activity were altered to protect cells from oxidative damage. Inverted biomicroscopy images showed that the microalgae enhanced their cell size to adapt to the environmental stress as exposed to 1 mg/L nCu. Scanning electron microscope (SEM) images showed that 10 mg/L nSiO2 could adsorb nCu and reduce the toxic effect of nCu on the microalgae, while 30 mg/L nSiO2 caused mechanical damage to microalgal cells and accelerated the internalization of nanoparticles and Cu2+ in the cells.

Activation of endogenous tolerance to bleaching stress by high salinity in cloned endosymbiotic dinoflagellates from corals

BACKGROUND

Large-scale coral bleaching events have become increasingly frequent in recent years. This process occurs when corals are exposed to high temperatures and intense light stress, leading to an overproduction of reactive oxygen species (ROS) by their endosymbiotic dinoflagellates. The ROS buildup prompts corals to expel these symbiotic microalgae, resulting in the corals' discoloration. Reducing ROS production and enhancing detoxification processes in these microalgae are crucial to prevent the collapse of coral reef ecosystems. However, research into the cell physiology and genetics of coral symbiotic dinoflagellates has been hindered by challenges associated with cloning these microalgae.

RESULTS

A procedure for cloning coral symbiotic dinoflagellates was developed in this study. Several species of coral symbionts were successfully cloned, with two of them further characterized. Experiments with the two species isolated from Turbinaria sp. showed that damage from light intensity at 340 μmol photons/m2/s was more severe than from high temperature at 36 °C. Additionally, preincubation in high salinity conditions activated their endogenous tolerance to bleaching stress. Pretreatment at 50 ppt salinity reduced the percentage of cells stained for ROS by 59% and 64% in the two species under bleaching stress compared to those incubated at 30 ppt. Furthermore, their Fv'/Fm' during the recovery period showed a significant improvement compared to the controls.

CONCLUSIONS

These findings suggest that intense light plays a more important role than high temperatures in coral bleaching by enhancing ROS generation in the symbiotic dinoflagellates. The findings also suggest the genomes of coral symbiotic dinoflagellates have undergone evolutionary processes to develop mechanisms, regulated by gene expression, to mitigate damages caused by high temperature and high light stress. Understanding this gene expression regulation could contribute to strengthening corals' resilience against the impact of global climate change.

Effect of glutathione reductase on photosystem II characterization and reactive oxygen species metabolism in cotton cytoplasmic male sterile line Jin A

Glutathione reductase (GR) maintains the cellular redox state by reducing oxidized glutathione to glutathione (GSH), which regulates antioxidant defense. Additionally, GR plays an essential role in photosynthesis; however, the mechanism by which GR regulates photosystem II (PSII) is largely unknown. We identified six, three, and three GR genes in Gossypium hirsutum, Gossypium arboreum, and Gossypium raimondii, respectively. We found that GhGR1 and GhGR3 proteins were localized in the chloroplasts, whereas GhGR5 was localized in the cell membrane. Cytoplasmic male sterile (CMS) line Jin A was ideal to explore GR functions because accumulation of reactive oxygen species (ROS) was increased and expression of GhGR was downregulated at the key stage of microspore abortion in anthers compared to maintainer Jin B. The GR activity and relative GhGR1, GhGR3, GhGR5 gene expressions decreased significantly at the key stage of microspore abortion in Jin A-CMS compared to that in Jin B, resulting in an increase in ROS and a decrease in photochemical efficiency in PSII. GhGR1 and GhGR3 overexpression in Arabidopsis decreased ROS levels in anthers and leaves compared to the wild-type. Biochemical analysis of GhGR1 and GhGR3 silencing in Gossypium L. showed that ROS content was increased and photochemical efficiency of PSII was inhibited in leaves. Complementation experiments in tobacco and yeast indicated that GhGR1 interacted with GhPsbX, which was one of the subunits of the PSII protein complex. Taken together, these findings suggest that chloroplast GR plays an important role in PSII and ROS metabolism by interacting with PsbX in cotton plants.

Effects of acid and aluminum stress on seed germination and physiological characteristics of seedling growth in Sophora davidii

Sophora davidii, a vital forage species, predominantly thrives in the subtropical karst mountains of Southwest China. Its resilience to poor soil conditions and arid environments renders it an ideal pioneer species for ecological restoration in these regions. This study investigates the influence of acidic, aluminum-rich local soil on the germination and seedling growth physiology of S. davidii. Experiments were conducted under varying degrees of acidity and aluminum stress, employing three pH levels (3.5 to 5.5) and four aluminum concentrations (0.5 to 2.0 mmol·L-1). The results showed that germination rate, germination index, and vigor index of S. davidii seeds were decreased but not significantly under slightly acidic conditions (pH 4.5-5.5), while strong acid (pH = 3.5) significantly inhibited the germination rate, germination index, and vigor index of white spurge seeds compared with the control group. Aluminum stress (≥0.5 mmol·L-1) significantly inhibited the germination rate, germination index, and vigor index of S. davidii seed. Moreover, the seedlings' root systems were sensitive to the changes of aluminum concentration, evident from significant root growth inhibition, characterized by root shortening and color deepening. Notably, under aluminum stress (pH = 4.3), the levels of malondialdehyde and proline in S. davidii escalated with increasing aluminum concentration, while antioxidant enzyme activities demonstrated an initial increase followed by a decline. The study underscores the pivotal role of cellular osmoregulatory substances and protective enzymes in combating aluminum toxicity in S. davidii, a key factor exacerbating growth inhibition in acidic environments. These findings offer preliminary theoretical insights for the practical agricultural utilization of S. davidii in challenging soil conditions.

A Chimeric Peptide for Shielding Plant Photosynthetic Systems against Excess Light Stress via Chloroplast-Targeted ROS Quenching

The ability to quench reactive oxygen species (ROS) overproduced in plant chloroplasts under light stress conditions is essential for securing plant photosynthetic performance and agricultural yield. Although genetic engineering can enhance plant stress resistance, its widespread application faces limitations due to challenges in successful transformation across plant species and public acceptance concerns. This study proposes a nontransgenic chemical approach using a designed chimeric peptide that scavenges ROS within plant chloroplasts for managing light stress. The chimeric peptide was strategically designed by combining cell-penetrating and chloroplast-targeting sequences, each with antioxidant ability against destructive ROS such as hydroxyl radical (•OH) and singlet oxygen (1O2). Our analyses involving various cell-penetrating peptides and a chloroplast-targeting peptide revealed that the •OH-scavenging ability predominantly relied on side chain oxidation in tryptophan residues, while the 1O2-quenching capacity was attributed to the oxidation of cysteine and methionine side chains. We further demonstrated that the chimeric peptide could traverse the cell wall and membranes to reach chloroplasts, where it scavenged •OH and 1O2 and alleviated light-stress-induced chlorophyll degradation in leaves. Foliar spraying of the peptide successfully protected photosynthetic activity in leaves exposed to excessive light, highlighting its potential for practical agricultural applications. This work can offer a promising approach for managing abiotic stress without genetic modifications and provide valuable insights into the design of effective peptide-based ROS quenchers specifically targeting plant chloroplasts.

Aquaporin CmPIP2;3 links H2O2 signal and antioxidation to modulate trehalose-induced cold tolerance in melon seedlings

Cold stress severely restricts the growth and development of cold-sensitive crops. Trehalose (Tre), known as the "sugar of life", plays key roles in regulating plant cold tolerance by triggering antioxidation. However, the relevant regulatory mechanism remains unclear. Here, we confirmed that Tre triggers apoplastic hydrogen peroxide (H2O2) production and thus plays key roles in improving the cold tolerance of melon (Cucumis melo var. makuwa Makino) seedlings. Moreover, Tre treatment can promote the transport of apoplastic H2O2 to the cytoplasm. This physiological process may depend on aquaporins. Further studies showed that a Tre-responsive plasma membrane intrinsic protein 2;3 (CmPIP2;3) had strong H2O2 transport function and that silencing CmPIP2;3 significantly weakened apoplastic H2O2 transport and reduced the cold tolerance of melon seedlings. Yeast library and protein-DNA interaction technology were then used to screen 2 Tre-responsive transcription factors, abscisic acid-responsive element (ABRE)-binding factor 2 (CmABF2) and ABRE-binding factor 3 (CmABF3), which can bind to the ABRE motif of the CmPIP2;3 promoter and activate its expression. Silencing of CmABF2 and CmABF3 further dramatically increased the ratio of apoplastic H2O2/cytoplasm H2O2 and reduced the cold tolerance of melon seedlings. This study uncovered that Tre treatment induces CmABF2/3 to positively regulate CmPIP2;3 expression. CmPIP2;3 subsequently enhances the cold tolerance of melon seedlings by promoting the transport of apoplastic H2O2 into the cytoplasm for conducting redox signals and stimulating downstream antioxidation.

The Ameliorative Effect of Coumarin on Copper Toxicity in Citrus sinensis: Insights from Growth, Nutrient Uptake, Oxidative Damage, and Photosynthetic Performance

Excessive copper (Cu) has become a common physiological disorder restricting the sustainable production of citrus. Coumarin (COU) is a hydroxycinnamic acid that can protect plants from heavy metal toxicity. No data to date are available on the ameliorative effect of COU on plant Cu toxicity. 'Xuegan' (Citrus sinensis (L.) Osbeck) seedlings were treated for 24 weeks with nutrient solution containing two Cu levels (0.5 (Cu0.5) and 400 (Cu400) μM CuCl2) × four COU levels (0 (COU0), 10 (COU10), 50 (COU50), and 100 (COU100) μM COU). There were eight treatments in total. COU supply alleviated Cu400-induced increase in Cu absorption and oxidative injury in roots and leaves, decrease in growth, nutrient uptake, and leaf pigment concentrations and CO2 assimilation (ACO2), and photo-inhibitory impairment to the whole photosynthetic electron transport chain (PETC) in leaves, as revealed by chlorophyll a fluorescence (OJIP) transient. Further analysis suggested that the COU-mediated improvement of nutrient status (decreased competition of Cu2+ with Mg2+ and Fe2+, increased uptake of nutrients, and elevated ability to maintain nutrient balance) and mitigation of oxidative damage (decreased formation of reactive oxygen species and efficient detoxification system in leaves and roots) might lower the damage of Cu400 to roots and leaves (chloroplast ultrastructure and PETC), thereby improving the leaf pigment levels, ACO2, and growth of Cu400-treated seedlings.

Functional interaction of melatonin with gasotransmitters and ROS in plant adaptation to abiotic stresses

Melatonin is considered a multifunctional stress metabolite and a novel plant hormone affecting seed germination, root architecture, circadian rhythms, leaf senescence, and fruit ripening. Melatonin functions related to plant adaptation to stress stimuli of various natures are considered especially important. One of the key components of melatonin's stress-protective action is its ability to neutralise reactive oxygen species (ROS) and reactive nitrogen species directly. However, many of its effects are related to its involvement in the signalling network of plant cells and its influence on the expression of a large number of genes important for adaptation to adverse factors. Insights into the functional relationships of melatonin with gasotransmitters (GT) - gaseous molecules performing signalling functions - are still emerging. This review has analysed and summarised the experimental data that testify to the participation of the main GTs - nitric oxide, hydrogen sulfide, and carbon monoxide - in the implementation of the protective effect of melatonin when plants are exposed to abiotic stimuli of various nature. In addition, modulation by melatonin of one of the most important components in the action of GTs and ROS - post-translational modifications of proteins and the influence of ROS and GTs on melatonin synthesis in plants under stress conditions and the specific physiological effects of exogenous melatonin and GTs have been reviewed. Finally, the prospects of the GTs' practical application to achieve synergistic stress-protective effects on plants have been considered.

Detrimental effects of UV-A radiation on antioxidant capacity and photosynthetic efficiency on a tropical microalga

Antioxidants are molecules able to neutralize reactive oxygen species with potential applications in the cosmetic or nutraceutical industries. Abiotic stressors, such as light intensity, ultraviolet (UV) radiation, or nutrient availability, can influence their production. In the perspective of optimizing and understanding the antioxidant capacity of microalgae, we investigated the effects of UV-A radiation on growth, and antioxidant and photosynthetic activities on Tetraselmis, a microalga genus known for its high antioxidant capacity. Cultures were exposed to UV-A radiation alongside to photosynthetically active radiation (PAR) in photobioreactors operated in continuous culture. UV-A exposure affects both the photosynthetic and antioxidant activities of Tetraselmis. Photosynthetic parameters suggest that UV-A has a negative effect on photosynthetic efficiency, particularly on the electron transport chain on short-term exposure (1-2 days). However, a resilience of most physiological parameters was observed over the experiment (10 days) suggesting a photochemical adaption over long-term exposure to UV-A radiation. Concerning the antioxidant capacity, UV-A exposure reduced the antioxidant capacity in Tetraselmis suggesting the use of antioxidant molecules to counteract reactive oxygen species production and prevent damage to photosystem II. Finally, the highest antioxidant capacity never observed with a Tetraselmis sp. was measured in cultures without UV addition, with an IC50 of 2.87 ± 0.24 µg mL-1, a value close to the reference compounds Trolox and α-tocopherol. This study showed the great potential of Tetraselmis as a source of antioxidants under favorable culture condition and without UV-A radiations. Indeed, we discourage the use of UV-A to enhance antioxidant capacity in this species due to its negative impact on it and on the photosynthetic efficiency.

ROS, an Important Plant Growth Regulator in Root Growth and Development: Functional Genes and Mechanism

Roots are fundamental to the growth, development, and survival of plants. Beyond anchoring the plant, roots absorb water and nutrients, supporting the plant's ability to grow and function normally. Root systems, originating from the apical meristem, exhibit significant diversity depending on the plant species. ROS are byproducts of aerobic metabolism, present in both above- and below-ground plant tissues. While ROS were once considered merely harmful byproducts of oxygen metabolism, they are now recognized as critical signaling molecules that regulate plant growth and development. Under stress conditions, plants produce elevated levels of ROS, which can inhibit growth. However, moderate ROS levels act as signals that integrate various regulatory pathways, contributing to normal plant development. However, there is still a lack of comprehensive and systematic research on how ROS precisely regulate root growth and development. This review provides an overview of ROS production pathways and their regulatory mechanisms in plants, with a particular focus on their influence on root development.

The regulatory roles of a plant neurotransmitter, acetylcholine, on growth, PSII photochemistry and antioxidant systems in wheat exposed to cadmium and/or mercury stress

Heavy metals increase in nature due to anthropogenic activities and negatively impact the growth, progress, and efficiency of plants. Among the toxic metal pollutants that can cause dangerous effects when accumulated by plants, mercury (Hg) and cadmium (Cd) were investigated in this study. These metals typically inhibit important enzymes and halt their functioning, thereby adversely affecting the capability of plants to achieve photosynthesis, respiration, and produce quality crops. Acetylcholine (ACh) serves as a potent neurotransmitter present in both primitive and advanced plant species. Its significant involvement in diverse metabolic processes, particularly in regulating growth and adaptation to stress, needs to be further elucidated. For this aim, effects of acetylcholine (ACh1, 10 μM; ACh2, 100 μM) were survey in Triticum aestivum under Hg and/or Cd stress (Hg, 50 μM; Cd, 100 μM). Wheat seedlings exhibited a growth retardation of about 24% under Hg or Cd stress. Combined stress conditions (Cd + Hg) resulted in a decrease in RWC by approximately 16%. Two different doses of ACh treatment to stressed plants positively affected growth parameters and regulated the water relations. Gas exchange was limited in stress groups, and the photochemical quantum competency of PSII (Fv/Fm) was suppressed. Cd + ACh1 and Cd + ACh2 treatments resulted in approximately 2-fold and 1.5-fold improvement in stomatal conductance and carbon assimilation rate, respectively. Similarly, improvement was observed with ACh treatments in wheat seedlings under Hg stress. Under Cd and/or Hg stress, high levels of H2O2 accumulated and lipid peroxidation occurred. According to our results, ACh treatment upon Cd and Hg stresses improved the activities of SOD, POX, and APX, thereby reducing oxidative damage. In conclusion, ACh treatment was found to ensure stress tolerance and limit the adverse effects caused by heavy metals.

The mechanisms of photoinhibition and repair in plants under high light conditions and interplay with abiotic stressors

This review comprehensively examines the phenomenon of photoinhibition in plants, focusing mainly on the intricate relationship between photodamage and photosystem II (PSII) repair and the role of PSII extrinsic proteins and protein phosphorylation in these processes. In natural environments, photoinhibition occurs together with a suite of concurrent stress factors, including extreme temperatures, drought and salinization. Photoinhibition, primarily caused by high irradiance, results in a critical imbalance between the rate of PSII photodamage and its repair. Central to this process is the generation of reactive oxygen species (ROS), which not only impair the photosynthetic apparatus first PSII but also play a signalling role in chloroplasts and other cellulular structures. ROS generated under stress conditions inhibit the repair of photodamaged PSII by suppressing D1 protein synthesis and affecting PSII protein phosphorylation. Furthermore, this review considers how environmental stressors exacerbate PSII damage by interfering with PSII repair primarily by reducing de novo protein synthesis. In addition to causing direct damage, these stressors also contribute to ROS production by restricting CO2 fixation, which also reduces the intensity of protein synthesis. This knowledge has significant implications for agricultural practices and crop improvement under stressful conditions.

Assessing the impact of arsenite and arsenate on Sarcodia suae: a tale of two toxicities

Inorganic arsenic (iAs), which predominantly occurs as arsenite (As3+) and arsenate (As5+) in natural water, is primarily accumulated by seaweed in marine environments. However, the detailed mechanisms through which As3+ and As5+ affect the physiological processes of these organisms remain largely unknown. This study focused on evaluating the toxicological effects of As3+ and As5+ on the seaweed Sarcodia suae. Exposure to As3+ and As5+ resulted in IC50 values of 401.5 ± 9.4 μg L-1 and 975.8 ± 13 μg L-1, respectively. Morphological alterations and a reduction in phycoerythrin content were observed, particularly under As3+ exposure, with increased lipid peroxidation as evidenced by higher malondialdehyde levels. Exposure to As3+ also elevated the production of superoxide radicals, while decreasing hydrogen peroxide levels specifically in the presence of As3+. The induction of antioxidative enzyme activities, namely superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase was observed, signaling an adaptive response to iAs-induced oxidative stress. Moreover, levels of the antioxidants ascorbate and glutathione were elevated post-exposure, especially in response to As3+. Additionally, bioaccumulation of arsenic was significantly higher in the As3+ compared to As5+. Collectively, the data suggest that As3+ imposes greater adverse effects and oxidative stress to S. suae, which responds by adjusting its antioxidative defense mechanisms to mitigate oxidative stress.

L-gulono-γ-lactone Oxidase, the Key Enzyme for L-Ascorbic Acid Biosynthesis

L-ascorbic acid (AsA, vitamin C) plays a vital role in preventing various diseases, particularly scurvy. AsA is known for its antioxidant properties, which help protect against reactive oxygen species generated from metabolic activities; however, at high doses, it may exhibit pro-oxidative effects. The final step in AsA biosynthesis is catalyzed by L-gulono-γ-lactone oxidase (GULO). This enzyme is present in many organisms, but some animals, including humans, guinea pigs, bats, and other primates, are unable to synthesize AsA due to the absence of a functional GULO gene. The GULO enzyme belongs to the family of aldonolactone oxidoreductases (AlORs) and contains two conserved domains, an N-terminal FAD-binding region and a C-terminal HWXK motif capable of binding the flavin cofactor. In this review, we explore AsA production, the biosynthetic pathways of AsA, and the localization of GULO-like enzymes in both animal and plant cells. Additionally, we compare the amino acid sequences of AlORs across different species and summarize the findings related to their enzymatic activity. Interestingly, a recombinant C-terminal rat GULO (the cytoplasmic domain of the rat GULO expressed in Escherichia coli) demonstrated enzymatic activity. This suggests that the binding of the flavin cofactor to the HWXK motif at the C-terminus is sufficient for the formation of the enzyme's active site. Another enzyme, GULLO7 from Arabidopsis thaliana, also lacks the N-terminal FAD-binding domain and is strongly expressed in mature pollen, although its activity has not been specifically measured.

Hormetic responses to cadmium exposure in wheat seedlings: insights into morphological, physiological, and biochemical adaptations

Cadmium is commonly recognized as toxic to plant growth, low-level Cd has promoting effects on growth performance, which is so-called hormesis. Although Cd toxicity in wheat has been widely investigated, knowledge of growth response to a broad range of Cd concentrations, especially extremely low concentrations, is still unknown. In this study, the morphological, physiological, and biochemical performance of wheat seedlings to a wide range of Cd concentrations (0-100 µΜ) were explored. Low Cd treatment (0.1-0.5 µM) improved wheat biomass and root development by enhancing the photosynthetic system and antioxidant system ability. Photosynthetic rate (Pn) was improved by 5.72% under lower Cd treatment (1 µΜ), but inhibited by 6.05-49.85% from 5 to 100 µΜ. Excessive Cd accumulation induced oxidative injury manifesting higher MDA content, resulting in lower photosynthetic efficiency, stunted growth, and reduction of biomass. Further, the contents of ascorbate, glutathione, non-protein thiols, and phytochelatins were improved under 5-100 µΜ Cd treatment. The ascorbate peroxidase activity in the leaf showed a hormetic dose-response characteristic. Correlation analysis and partial least squares (PLS) results indicated that antioxidant enzymes and metabolites were closely correlated with Cd tolerance and accumulation. The results of the element network, correlation analysis, and PLS showed a crucial role for exogenous Cd levels in K, Fe, Cu, and Mn uptake and accumulation. These results provided a deeper understanding of the hormetic effect of Cd in wheat, which would be beneficial for improving the quality of hazard and risk assessments.

Effects of Nitrogen Deficiency on the Photosynthesis, Chlorophyll a Fluorescence, Antioxidant System, and Sulfur Compounds in Oryza sativa

Decreasing nitrogen (N) supply affected the normal growth of Oryza sativa (O. sativa) seedlings, reducing CO2 assimilation, stomatal conductance (gs), the contents of chlorophylls (Chl) and the ratio of Chl a/Chl b, but increasing the intercellular CO2 concentration. Polyphasic chlorophyll a fluorescence transient and relative fluorescence parameters (JIP test) results indicated that N deficiency increased Fo, but decreased the maximum quantum yield of primary photochemistry (Fv/Fm) and the maximum of the IPphase, implying that N-limiting condition impaired the whole photo electron transport chain from the donor side of photosystem II (PSII) to the end acceptor side of PSI in O. sativa. N deficiency enhanced the activities of the antioxidant enzymes, such as ascorbate peroxidase (APX), guaiacol peroxidase (GuPX), dehydro-ascorbate reductase (DHAR), superoxide dismutase (SOD), glutathione peroxidase (GlPX), glutathione reductase (GR), glutathione S-transferase (GST) and O-acetylserine (thiol) lyase (OASTL), and the contents of antioxidant compounds including reduced glutathione (GSH), total glutathione (GSH+GSSG) and non-protein thiol compounds in O. sativa leaves. In contrast, the enhanced activities of catalase (CAT), DHAR, GR, GST and OASTL, the enhanced ASC-GSH cycle and content of sulfur-containing compounds might provide protective roles against oxidative stress in O. sativa roots under N-limiting conditions. Quantitative real-time PCR (qRT-PCR) analysis indicated that 70% of the enzymes have a consistence between the gene expression pattern and the dynamic of enzyme activity in O. sativa leaves under different N supplies, whereas only 60% of the enzymes have a consistence in O. sativa roots. Our results suggested that the antioxidant system and sulfur metabolism take part in the response of N limiting condition in O. sativa, and this response was different between leaves and roots. Future work should focus on the responsive mechanisms underlying the metabolism of sulfur-containing compounds in O. sativa under nutrient deficient especially N-limiting conditions.

Cytosolic acidification and oxidation are the toxic mechanisms of SO2 in Arabidopsis guard cells

SO2/H2SO3 can damage plants. However, its toxic mechanism has still been controversial. Two models have been proposed, cytosolic acidification model and cellular oxidation model. Here, we assessed the toxic mechanism of H2SO3 in three cell types of Arabidopsis thaliana, mesophyll cells, guard cells (GCs), and petal cells. The sensitivity of GCs of Chloride channel a (CLCa)-knockout mutants to H2SO3 was significantly lower than those of wildtype plants. Expression of other CLC genes in mesophyll cells and petal cells were different from GCs. Treatment with antioxidant, disodium 4,5-dihydroxy-1,3-benzenedisulfonate (tiron), increased the median lethal concentration (LC50) of H2SO3 in GCs indicating the involvement of cellular oxidation, while the effect was negligible in mesophyll cells and petal cells. These results indicate that there are two toxic mechanisms of SO2 to Arabidopsis cells: cytosolic acidification and cellular oxidation, and the toxic mechanism may vary among cell types.

Deciphering the Mechanism of Melatonin-Induced Enhancement of Photosystem II Function in Moderate Drought-Stressed Oregano Plants

Melatonin (MT) is considered as an antistress molecule that plays a constructive role in the acclimation of plants to both biotic and abiotic stress conditions. In the present study, we assessed the impact of 10 and 100 μM MT foliar spray, on chlorophyll content, and photosystem II (PSII) function, under moderate drought stress, on oregano (Origanum vulgare L.) plants. Our aim was to elucidate the molecular mechanism of MT action on the photosynthetic electron transport process. Foliar spray with 100 μM MT was more effective in mitigating the negative impact of moderate drought stress on PSII function, compared to 10 μM MT. MT foliar spray significantly improved the reduced efficiency of the oxygen-evolving complex (OEC), and PSII photoinhibition (Fv/Fm), which were caused by drought stress. Under moderate drought stress, foliar spray with 100 μM MT, compared with the water sprayed (WA) leaves, increased the non-photochemical quenching (NPQ) by 31%, at the growth irradiance (GI, 205 μmol photons m-2 s-1), and by 13% at a high irradiance (HI, 1000 μmol photons m-2 s-1). However, the lower NPQ increase at HI was demonstrated to be more effective in decreasing the singlet-excited oxygen (1O2) production at HI (-38%), in drought-stressed oregano plants sprayed with 100 μM MT, than the corresponding decrease in 1O2 production at the GI (-20%), both compared with the respective WA-sprayed leaves under moderate drought. The reduced 1O2 production resulted in a significant increase in the quantum yield of PSII photochemistry (ΦPSII), and the electron transport rate (ETR), in moderate drought-stressed plants sprayed with 100 μM MT, compared with WA-sprayed plants, but only at the HI (+27%). Our results suggest that the enhancement of PSII functionality, with 100 μM MT under moderate drought stress, was initiated by the NPQ mechanism, which decreased the 1O2 production and increased the fraction of open PSII reaction centers (qp), resulting in an increased ETR.

Vacuolar degradation of plant organelles

Plants continuously remodel and degrade their organelles due to damage from their metabolic activities and environmental stressors, as well as an integral part of their cell differentiation programs. Whereas certain organelles use local hydrolytic enzymes for limited remodeling, most of the pathways that control the partial or complete dismantling of organelles rely on vacuolar degradation. Specifically, selective autophagic pathways play a crucial role in recognizing and sorting plant organelle cargo for vacuolar clearance, especially under cellular stress conditions induced by factors like heat, drought, and damaging light. In these short reviews, we discuss the mechanisms that control the vacuolar degradation of chloroplasts, mitochondria, endoplasmic reticulum, Golgi, and peroxisomes, with an emphasis on autophagy, recently discovered selective autophagy receptors for plant organelles, and crosstalk with other catabolic pathways.

Arbuscular mycorrhizal fungi alter carbon metabolism and invertase genes expressions of Populus simonii × P. nigra under drought stress

Arbuscular mycorrhizal fungi (AMF) play a crucial role in regulating the allocation of carbon between source and sink tissues in plants and in regulating their stress responses by changing the sucrose biosynthesis, transportation, and catabolism in plants. Invertase, a key enzyme for plant development, participates in the response of plants to drought stress by regulating sucrose metabolism. However, the detailed mechanisms by which INV genes respond to drought stress in mycorrhizal plants remain unclear. This study examined the sugar content, enzyme activity, and expression profiles of INV genes of Populus simonii × P. nigra (PsnINVs) under two inoculation treatments (inoculation or non-inoculation) and two water conditions (well-watered or drought stress). Results showed that under drought stress, AMF up-regulated the expressions of PsnA/NINV1, PsnA/NINV2, PsnA/NINV3, and PsnA/NINV5 in leaves, which may be related to the enhancement of photosynthetic capacity. Additionally, AMF up-regulated the expressions of PsnA/NINV6, PsnA/NINV10, and PsnA/NINV12 in leaves, which may be related to enhancing osmotic regulation ability and drought tolerance.

Tuber quality enhancement via grafting potato onto a wooden goji rootstock through vitalizing multi-pathways

Grafting is applied in Solanaceae to improve growth and quality traits. However, grafting potato onto a wooden goji rootstock is rare. Our study introduces a novel distant grafting technique to investigate potato scion responses, specifically regarding photosynthetic and tuber nutritional quality. The physiological and transcriptomic findings reveal an increase in photosynthesis ratio and carbon fixation in potato leaves after 45 days of grafting due to the upregulation of pivotal genes (PsbA, PPC1, rbcl, and GAPDH). After 95 days of long-term growth, the leaf redox balance was maintained with intensified chlorophyll synthesis, facilitated by the enrichment of crucial genes (GUN4, CHLH, CHLP, CAO) and several light-harvesting proteins (Lhca and Lhcb) in potato leaves. The tubers of grafted plants showed a 6.5% increase in crude protein, 51% in anthocyanin, and lower carbohydrate content. Goji altered the expression of tubers genes involved in assimilatory sulfate reduction, which subsequently affects cysteine-methionine biosynthesis. Furthermore, the tuber transcriptome shows ABA signaling and transcription factors regulate the expression of key biosynthetic genes involved in inducing the secondary metabolites, such as scopoletin and anthocyanin accumulation, which are primary polyphenols in goji. Our innovative grafting approach offers valuable insights into the interactions between woody and herbaceous plants for developing future strategies to modulate growth efficiency and tuber quality in the face of climate challenges and to meet the demand for nutritious food.

The role of drought response genes and plant growth promoting bacteria on plant growth promotion under sustainable agriculture: A review

Drought is a major stressor that poses significant challenges for agricultural practices. It becomes difficult to meet the global demand for food crops and fodder. Plant physiology, physico-chemistry and morphology changes in plants like decreased photosynthesis and transpiration rate, overproduction of reactive oxygen species, repressed shoot and root shoot growth and modified stress signalling pathways by drought, lead to detrimental impacts on plant development and output. Coping with drought stress requires a variety of adaptations and mitigation techniques. Crop yields could be effectively increased by employing plant growth-promoting rhizobacteria (PGPR), which operate through many mechanisms. These vital microbes colonise the rhizosphere of crops and promote drought resistance by producing exopolysaccharides (EPS), 1-aminocyclopropane-1-carboxylate (ACC) deaminase and phytohormones including volatile compounds. The upregulation or downregulation of stress-responsive genes causes changes in root architecture due to acquiring drought resistance. Further, PGPR induces osmolyte and antioxidant accumulation. Another key feature of microbial communities associated with crops includes induced systemic tolerance and the production of free radical-scavenging enzymes. This review is focused on detailing the role of PGPR in assisting plants to adapt to drought stress.

Investigating the molecular mechanisms of Pseudalteromonas sp. LD-B1's algicidal effects on the harmful alga Heterosigma akashiwo

Heterosigma akashiwo is a harmful algal bloom species that causes significant detrimental effects on marine ecosystems worldwide. The algicidal bacterium Pseudalteromonas sp. LD-B1 has demonstrated potential effectiveness in mitigating these blooms. However, the molecular mechanisms underlying LD-B1's inhibitory effects on H. akashiwo remain poorly understood. In this study, we employed the comprehensive methodology, including morphological observation, assessment of photosynthetic efficiency (Fv/Fm), and transcriptomic analysis, to investigate the response of H. akashiwo to LD-B1. Exposure to LD-B1 resulted in a rapid decline of H. akashiwo's Fv/Fm ratio, with cells transitioning to a rounded shape within 2 hours, subsequently undergoing structural collapse and cytoplasmic leakage. Transcriptomic data revealed sustained downregulation of photosynthetic genes, indicating impaired functionality of the photosynthetic system. Additionally, genes related to the respiratory electron transfer chain and antioxidant defenses were consistently downregulated, suggesting prolonged oxidative stress beyond the cellular antioxidative capacity. Notably, upregulation of autophagy-related genes was observed, indicating autophagic responses in the algal cells. This study elucidates the molecular basis of LD-B1's algicidal effects on H. akashiwo, advancing our understanding of algicidal mechanisms and contributing to the development of effective strategies for controlling harmful algal blooms.

Nanobiotechnology-mediated regulation of reactive oxygen species homeostasis under heat and drought stress in plants

Global warming causes heat and drought stress in plants, which affects crop production. In addition to osmotic stress and protein inactivation, reactive oxygen species (ROS) overaccumulation under heat and drought stress is a secondary stress that further impairs plant performance. Chloroplasts, mitochondria, peroxisomes, and apoplasts are the main ROS generation sites in heat- and drought-stressed plants. In this review, we summarize ROS generation and scavenging in heat- and drought-stressed plants and highlight the potential applications of plant nanobiotechnology for enhancing plant tolerance to these stresses.

Overexpression of Rhodiola crenulata glutathione peroxidase 5 increases cold tolerance and enhances the pharmaceutical value of the hairy roots

Rhodiola crenulata, a plant of great medicinal value found in cold high-altitude regions, has been excessively exploited due to the difficulty in cultivation. Understanding Rhodiola crenulata's adaptation mechanisms to cold environment can provide a theoretical basis for artificial breeding. Glutathione peroxidases (GPXs), critical enzymes found in plants, play essential roles in antioxidant defense through the ascorbate-glutathione cycle. However, it is unknown whether GPX5 contributes to Rhodiola crenulata's cold tolerance. In this study, we investigated the role of GPX5 in Rhodiola crenulata's cold tolerance mechanisms. By overexpressing Rhodiola crenulata GPX5 (RcGPX5) in yeast and Arabidopsis thaliana, we observed down-regulation of Arabidopsis thaliana GPX5 (AtGPX5) and increased cold tolerance in both organisms. Furthermore, the levels of antioxidants and enzyme activities in the ascorbate-glutathione cycle were elevated, and cold-responsive genes such as AtCBFs and AtCORs were induced. Additionally, RcGPX5 overexpressing lines showed insensitivity to exogenous abscisic acid (ABA), suggesting a negative regulation of the ABA pathway by RcGPX5. RcGPX5 also promoted the expression of several thioredoxin genes in Arabidopsis and interacted with two endogenous genes of Rhodiola crenulata, RcTrx2-3 and RcTrxo1, located in mitochondria and chloroplasts. These findings suggest a significantly different model in Rhodiola crenulata compared to Arabidopsis thaliana, highlighting a complex network involving the function of RcGPX5. Moreover, overexpressing RcGPX5 in Rhodiola crenulata hairy roots positively influenced the salidroside synthesis pathway, enhancing its pharmaceutical value for doxorubicin-induced cardiotoxicity. These results suggested that RcGPX5 might be a key component for Rhodiola crenulata to adapt to cold stress and overexpressing RcGPX5 could enhance the pharmaceutical value of the hairy roots.

Heliotropium thermophilum adapts to high soil temperature in natural conditions due to its highly active antioxidant system protecting its photosynthetic machinery

Heliotropium thermophilum (Boraginaceae) plants have strong antioxidant properties. This study investigated the effectiveness of the antioxidant system in protecting the photosynthetic machinery of H. thermophilum . Plants were obtained from Kızıldere geothermal area in Buharkent district, Aydın, Turkey. Plants in the geothermal area that grew at 25-35°C were regarded as the low temperature group, while those that grew at 55-65°C were regarded as the high temperature group. We analysed the physiological changes of these plants at the two temperature conditions at stage pre-flowering and flowering. We meaured the effect of high soil temperature on water potential, malondialdehyde, cell membrane stability, and hydrogen peroxide analysis to determine stress levels on leaves and roots. Changes in antioxidant enzyme activities, ascorbate and chlorophyll content, chlorophyll fluorescence, photosynthetic gas exchange parameters, and photosynthetic enzymes (Rubisco and invertase) activities were also determined. Our results showed minimal changes to stress levels, indicating that plants were tolerant to high soil temperatures. In general, an increase in antioxidant enzyme activities, ascorbat levels, and all chlorophyll fluorescence parameters except for non-photochemical quenching (NPQ) and F v /F m were observed. The pre-flowering and flowering stages were both characterised by decreased NPQ, despite F v /F m not changing. Additionally, there was a rise in the levels of photosynthetic gas exchange parameters, Rubisco, and invertase activities. High temperature did not affect photosynthetic yield because H. thermophilum was found to stimulate antioxidant capacity, which reduces oxidative damage and maintains its photosynthetic machinery in high temperature conditions and therefore, it is tolerant to high soil temperature.

Revisiting the role of ascorbate oxidase in plant systems

Ascorbic acid (AsA) plays an indispensable role in plants, serving as both an antioxidant and a master regulator of the cellular redox balance. Ascorbate oxidase (AO) is a blue copper oxidase that is responsible for the oxidation of AsA with the concomitant production of water. For many decades, AO was erroneously postulated as an enzyme without any obvious advantage, as it decreases the AsA pool size and thus is expected to weaken plant stress resistance. It was only a decade ago that this perspective shifted towards the fundamental role of AO in orchestrating both AsA and oxygen levels by influencing the overall redox balance in the extracellular matrix. Consistent with its localization in the apoplast, AO is involved in cell expansion, division, resource allocation, and overall plant yield. An increasing number of transgenic studies has demonstrated that AO can also facilitate communication between the surrounding environment and the cell, as its gene expression is highly responsive to factors such as hormonal signaling, oxidative stress, and mechanical injury. This review aims to describe the multiple functions of AO in plant growth, development, and stress resilience, and explore any additional roles the enzyme might have in fruits during the course of ripening.

The ascorbate biosynthesis pathway in plants is known, but there is a way to go with understanding control and functions

Ascorbate (vitamin C) is one of the most abundant primary metabolites in plants. Its complex chemistry enables it to function as an antioxidant, as a free radical scavenger, and as a reductant for iron and copper. Ascorbate biosynthesis occurs via the mannose/l-galactose pathway in green plants, and the evidence for this pathway being the major route is reviewed. Ascorbate accumulation is leaves is responsive to light, reflecting various roles in photoprotection. GDP-l-galactose phosphorylase (GGP) is the first dedicated step in the pathway and is important in controlling ascorbate synthesis. Its expression is determined by a combination of transcription and translation. Translation is controlled by an upstream open reading frame (uORF) which blocks translation of the main GGP-coding sequence, possibly in an ascorbate-dependent manner. GGP associates with a PAS-LOV protein, inhibiting its activity, and dissociation is induced by blue light. While low ascorbate mutants are susceptible to oxidative stress, they grow nearly normally. In contrast, mutants lacking ascorbate do not grow unless rescued by supplementation. Further research should investigate possible basal functions of ascorbate in severely deficient plants involving prevention of iron overoxidation in 2-oxoglutarate-dependent dioxygenases and iron mobilization during seed development and germination.

PbHsfC1a-coordinates ABA biosynthesis and H2O2 signalling pathways to improve drought tolerance in Pyrus betulaefolia

Abiotic stresses have had a substantial impact on fruit crop output and quality. Plants have evolved an efficient immune system to combat abiotic stress, which employs reactive oxygen species (ROS) to activate the downstream defence response signals. Although an aquaporin protein encoded by PbPIP1;4 is identified from transcriptome analysis of Pyrus betulaefolia plants under drought treatments, little attention has been paid to the role of PIP and ROS in responding to abiotic stresses in pear plants. In this study, we discovered that overexpression of PbPIP1;4 in pear callus improved tolerance to oxidative and osmotic stresses by reconstructing redox homeostasis and ABA signal pathways. PbPIP1;4 overexpression enhanced the transport of H2O2 into pear and yeast cells. Overexpression of PbPIP1;4 in Arabidopsis plants mitigates the stress effects caused by adding ABA, including stomatal closure and reduction of seed germination and seedling growth. Overexpression of PbPIP1;4 in Arabidopsis plants decreases drought-induced leaf withering. The PbPIP1;4 promoter could be bound and activated by TF PbHsfC1a. Overexpression of PbHsfC1a in Arabidopsis plants rescued the leaf from wilting under drought stress. PbHsfC1a could bind to and activate AtNCED4 and PbNCED4 promoters, but the activation could be inhibited by adding ABA. Besides, PbNCED expression was up-regulated under H2O2 treatment but down-regulated under ABA treatment. In conclusion, this study revealed that PbHsfC1a is a positive regulator of abiotic stress, by targeting PbPIP1;4 and PbNCED4 promoters and activating their expression to mediate redox homeostasis and ABA biosynthesis. It provides valuable information for breeding drought-resistant pear cultivars through gene modification.

Biochemical Responses in Populus tremula: Defending against Sucking and Leaf-Chewing Insect Herbivores

The main biochemical traits were estimated in poplar leaves under biotic attack (aphids and spongy moth infestation). Changes in the abundance of bioactive compounds in genetically uniform individuals of European aspen (Populus tremula), such as proline, polyphenolic compounds, chlorophylls a and b, and volatile compounds, were determined between leaves damaged by sucking insects (aphid-Chaitophorus nassonowi) and chewing insects (spongy moth-Lymantria dispar) compared to uninfected leaves. Among the nine analyzed phenolic compounds, only catechin and procyanidin showed significant differences between the control leaves and leaves affected by spongy moths or aphids. GC-TOF-MS volatile metabolome analysis showed the clear separation of the control versus aphids-infested and moth-infested leaves. In total, the compounds that proved to have the highest explanatory power for aphid-infested leaves were 3-hexenal and 5-methyl-2-furanone, and for moth-infested leaves, trans-α-farnesene and 4-cyanocyclohexane. The aphid-infested leaves contained around half the amount of chlorophylls and twice the amount of proline compared to uninfected leaves, and these results evidenced that aphids influence plant physiology more than chewing insects.

Host Plant Modulated Physio-Biochemical Process Enhances Adaptive Response of Sandalwood (Santalum album L.) under Salinity Stress

Salinity is one of the most significant abiotic stress that affects the growth and development of high-value tree species, including sandalwood, which can also be managed effectively on saline soils with the help of suitable host species. Therefore, the current investigation was conducted to understand the physiological processes and antioxidant mechanisms in sandalwood along the different salinity gradients to explore the host species that could support sandalwood growth in salt-affected agro-ecosystems. Sandalwood seedlings were grown with ten diverse host species with saline water irrigation gradients (ECiw~3, 6, and 9 dS m-1) and control (ECiw~0.82 dS m-1). Experimental findings indicate a decline in the chlorophyll content (13-33%), relative water content (3-23%), photosynthetic (27-61%) and transpiration rate (23-66%), water and osmotic potential (up to 137%), and ion dynamics (up to 61%) with increasing salinity levels. Conversely, the carotenoid content (23-43%), antioxidant activity (up to 285%), and membrane injury (82-205%) were enhanced with increasing salinity stress. Specifically, among the hosts, Dalbergia sissoo and Melia dubia showed a minimum reduction in chlorophyll content, relative water content, and plant water relation and gas exchange parameters of sandalwood plants. Surprisingly, most of the host tree species maintained K+/Na+ of sandalwood up to moderate water salinity of ECiw~6 dS m-1; however, a further increase in water salinity decreased the K+/Na+ ratio of sandalwood by many-fold. Salinity stress also enhanced the antioxidative enzyme activity, although the maximum increase was noted with host plants M. dubia, followed by D. sissoo and Azadirachta indica. Overall, the investigation concluded that sandalwood with the host D. sissoo can be successfully grown in nurseries using saline irrigation water and, with the host M. dubia, it can be grown using good quality irrigation water.

Genomic evidence for evolutionary history and local adaptation of two endemic apricots: Prunus hongpingensis and P. zhengheensis

Apricot, belonging to the Armeniaca section of Rosaceae, is one of the economically important crop fruits that has been extensively cultivated. The natural wild apricots offer valuable genetic resources for crop improvement. However, some of them are endemic, with small populations, and are even at risk of extinction. In this study we unveil chromosome-level genome assemblies for two southern China endemic apricots, Prunus hongpingensis (PHP) and P. zhengheensis (PZH). We also characterize their evolutionary history and the genomic basis of their local adaptation using whole-genome resequencing data. Our findings reveal that PHP and PZH are closely related to Prunus armeniaca and form a distinct lineage. Both species experienced a decline in effective population size following the Last Glacial Maximum (LGM), which likely contributed to their current small population sizes. Despite the observed decrease in genetic diversity and heterozygosity, we do not observe an increased accumulation of deleterious mutations in these two endemic apricots. This is likely due to the combined effects of a low inbreeding coefficient and strong purifying selection. Furthermore, we identify a set of genes that have undergone positive selection and are associated with local environmental adaptation in PHP and PZH, respectively. These candidate genes can serve as valuable genetic resources for targeted breeding and improvement of cultivated apricots. Overall, our study not only enriches our comprehension of the evolutionary history of apricot species but also offers crucial insights for the conservation and future breeding of other endemic species amidst rapid climate changes.

Effects of nitrate- and ammonium- nitrogen on anatomical and physiological responses of Catalpa bungei under full and partial root-zone drought

Catalpa bungei is a precious timber species distributed in North China where drought often occurs. To clarify adaptive responses of C. bungei to partial- and full- root-zone drought under the influence of nitrogen forms, a two-factor experiment was conducted in which well-watered (WW), partial root-zone drought in horizontal direction (H-PRD) and in vertical direction (V-PRD), and full root-zone drought (FRD) were combined with nitrate-nitrogen (NN) and ammonium-nitrogen (AN) treatments. C. bungei responded to FRD by sharply closing stomata, decreasing gas exchange rate and increasing leaf instantaneous water use efficiency (WUEi). Under FRD condition, the growth of seedlings was severely inhibited and the effect of N forms was covered up by the drastic drought effect. In comparison, stomata conductance and gas exchanges were moderately inhibited by PRDs. WUEi in V-PRD treatment was superior to H-PRD due to the active stomata regulation resulting from a higher ABA level and active transcription of genes in abscisic acid (ABA) signaling pathway under V-PRD. Under both PRDs and FRD, nitrate benefited antioxidant defense, stomata regulation and leaf WUEi. Under V-PRD, WUEi in nitrate treatment was superior to that in ammonium treatment due to active stomata regulation by signaling network of nitric oxide (NO), Ca2+ and ABA. Under FRD, WUEi was higher in nitrate treatment due to the favoring photosynthetic efficiency resulting from active NO signal and antioxidant defense. The interactive effect of water and N forms was significant on wood xylem development. Superoxide dismutase (SOD) and catalase (CAT) largely contributes to stress tolerance and xylem development.

Improved capacity for the repair of photosystem II via reinforcement of the translational and antioxidation systems in Synechocystis sp. PCC 6803

In the cyanobacterium Synechocystis sp. PCC 6803, translation factor EF-Tu is inactivated by reactive oxygen species (ROS) via oxidation of Cys82 and the oxidation of EF-Tu enhances the inhibition of the repair of photosystem II (PSII) by suppressing protein synthesis. In our present study, we generated transformants of Synechocystis that overexpressed a mutated form of EF-Tu, designated EF-Tu (C82S), in which Cys82 had been replaced by a Ser residue, and ROS-scavenging enzymes individually or together. Expression of EF-Tu (C82S) alone in Synechocystis enhanced the repair of PSII under strong light, with the resultant mitigation of PSII photoinhibition, but it stimulated the production of ROS. However, overexpression of superoxide dismutase and catalase, together with the expression of EF-Tu (C82S), lowered intracellular levels of ROS and enhanced the repair of PSII more significantly under strong light, via facilitation of the synthesis de novo of the D1 protein. By contrast, the activity of photosystem I was hardly affected in wild-type cells and in all the lines of transformed cells under the same strong-light conditions. Furthermore, transformed cells that overexpressed EF-Tu (C82S), superoxide dismutase, and catalase were able to survive longer under stronger light than wild-type cells. Thus, the reinforced capacity for both protein synthesis and ROS scavenging allowed both photosynthesis and cell proliferation to tolerate strong light.

Polyvinylpyrrolidone-coated copper nanoparticles dose-dependently conferred tolerance to wheat under salinity and/or drought stress by improving photochemical activity and antioxidant system

Copper (Cu) is one of the essential micronutrients for plants and has been used extensively in agricultural applications from the past to the present. However, excess copper causes toxic effects such as inhibiting photosynthesis, and disrupting biochemical processes in plants. Nanotechnology applications have offered a critical method for minimizing adverse effects and improving the effectiveness of copper nanoparticles. For this purpose, this study investigated the physiological and biochemical effects of polyvinylpyrrolidone (PVP)-coated Cu nanoparticles (PVP-Cu NP, N1, 100 mg L-1; N2, 400 mg L-1) in Triticum aestivum under alone or combined with salt (S, 150 mM NaCl) and/or drought (D, %10 PEG-6000) stress. Salinity and water deprivation caused 51% and 22% growth retardation in wheat seedlings. The combined stress condition (S + D) resulted in an approximately 3-fold reduction in the osmotic potential of the leaves. PVP-Cu NP treatments to plants under stress, especially N1 dose, were effective in restoring growth rate and regulating water relations. All stress treatments limited gas exchange in stomata and suppressed the maximal quantum yield of PSII (Fv/Fm). More than 50% improvement was observed in stomatal permeability and carbon assimilation rate under S + N1 and S + N2 applications. Examination of OJIP transient parameters revealed that N1 treatments protected photochemical reactions by reducing the dissipated energy flux (DIo/RC) in drought and S + D conditions. Exposure to S and/or D stress caused high hydrogen peroxide (H2O2) accumulation and lipid peroxidation in wheat leaves. The results indicated that S + N1 and S + N2 treatments reduced oxidative damage by stimulating the activities of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX). Although similar effects were observed at D and S + D conditions with 100 mg L-1 PVP-Cu NP treatments (N1), the curative effect of the N2 dose was not observed. In D + N1 and S + D + N1 groups, AsA regeneration and GSH redox status were maintained by triggering APX, GR, and other enzyme activities belonging to the AsA-GSH cycle. In these groups, N2 treatment did not contribute to the availability of enzymatic and non-enzymatic antioxidants. As a result, this study revealed that N1 dose PVP-Cu NP application was successful in providing stress tolerance and limiting copper-induced adverse effects under all stress conditions.

Nanoparticles for Mitigation of Harmful Cyanobacterial Blooms

With the rapid advancement of nanotechnology and its widespread applications, increasing amounts of manufactured and natural nanoparticles (NPs) have been tested for their potential utilization in treating harmful cyanobacterial blooms (HCBs). NPs can be used as a photocatalyst, algaecide, adsorbent, flocculant, or coagulant. The primary mechanisms explored for NPs to mitigate HCBs include photocatalysis, metal ion-induced cytotoxicity, physical disruption of the cell membrane, light-shielding, flocculation/coagulation/sedimentation of cyanobacterial cells, and the removal of phosphorus (P) and cyanotoxins from bloom water by adsorption. As an emerging and promising chemical/physical approach for HCB mitigation, versatile NP-based technologies offer great advantages, such as being environmentally benign, cost-effective, highly efficient, recyclable, and adaptable. The challenges we face include cost reduction, scalability, and impacts on non-target species co-inhabiting in the same environment. Further efforts are required to scale up to real-world operations through developing more efficient, recoverable, reusable, and deployable NP-based lattices or materials that are adaptable to bloom events in different water bodies of different sizes, such as reservoirs, lakes, rivers, and marine environments.

Impact of individual, combined and sequential stress on photosynthesis machinery in rice (Oryza sativa L)

Abiotic stresses such as heat, drought and submergence are major threats to global food security. Despite simultaneous or sequential occurrence of these stresses being recurrent under field conditions, crop response to such stress combinations is poorly understood. Rice is a staple food crop for the majority of human beings. Exploitation of existing genetic diversity in rice for combined and/or sequential stress is a useful approach for developing climate-resilient cultivars. We phenotyped ~400 rice accessions under high temperature, drought, or submergence and their combinations. A cumulative performance index revealed Lomello as the best performer across stress and stress combinations at the seedling stage. Lomello showed a remarkable ability to maintain a higher quantum yield of photosystem (PS) II photochemistry. Moreover, the structural integrity of the photosystems, electron flow through both PSI and PSII and the ability to protect photosystems against photoinhibition were identified as the key traits of Lomello across the stress environments. A higher membrane stability and an increased amount of leaf chlorophyll under stress may be due to an efficient management of reactive oxygen species (ROS) at the cellular level. Further, an efficient electron flow through the photosystems and, thus, a higher photosynthetic rate in Lomello is expected to act as a sink for ROS by reducing the rate of electron transport to the high amount of molecular oxygen present in the chloroplast. However, further studies are needed to identify the molecular mechanism(s) involved in the stability of photosynthetic machinery and stress management in Lomello during stress conditions.

Quercetin-mediated alteration in photosynthetic efficiency, sugar metabolism, elemental status, yield, and redox potential in two varieties of okra

Quercetin is a bioactive natural compound with an antioxidative property that can potentially modify plant physiology. The current investigation aimed to gauge the effect of different concentrations of foliar spray of quercetin (0, 0.5, 1, 1.5, 2.0 mM) on several morphological and physio-biochemical performances of Abelmoschus esculentus L. (Moench.) plants under normal environmental conditions. The foliar spray on the plant leaves was applied 25 days after sowing (DAS) and continued up to 30 DAS once each day. The plants were sampled at 30 and 45 DAS to monitor several parameters. The foliar treatments of quercetin significantly upgraded all the studied parameters. The results direct that most of the traits such as growth, nutrient uptake, photosynthetic, and enzyme activities were promoted in a dose-dependent way. Quercetin application lowered the reactive oxygen species (ROS) buildup by increasing the antioxidant enzyme activities. Microscopic investigations further revealed a significant enhancement in the stomatal aperture under quercetin application. Out of several doses tested, 1 mM of quercetin proved best and can be used for further investigations.

Genome-Wide Identification, Evolutionary Analysis, and Functional Studies of APX Genes in Melon (Cucuis melo L.)

The antioxidative enzyme ascorbate peroxidase (APX) exerts a critically important function through scavenging reactive oxygen species (ROS), alleviating oxidative damage in plants, and enhancing their tolerance to salinity. Here, we identified 28 CmAPX genes that display an uneven distribution pattern throughout the 12 chromosomes of the melon genome by carrying out a bioinformatics analysis. Phylogenetic analyses revealed that the CmAPX gene family comprised seven different clades, with each clade of genes exhibiting comparable motifs and structures. We cloned 28 CmAPX genes to infer their encoded protein sequences; we then compared these sequences with proteins encoded by rice APX proteins (OsAPX2), Puccinellia tenuiflora APX proteins (PutAPX) and with pea APX proteins. We found that the CmAPX17, CmAPX24, and CmAPX27 genes in Clade I were closely related, and their structures were highly conserved. CmAPX27 (MELO3C020719.2.1) was found to promote resistance to 150 mM NaCl salt stress, according to quantitative real-time fluorescence PCR. Transcriptome data revealed that CmAPX27 was differentially expressed among tissues, and the observed differences in expression were significant. Virus-induced gene silencing of CmAPX27 significantly decreased salinity tolerance, and CmAPX27 exhibited differential expression in the leaf, stem, and root tissues of melon plants. This finding demonstrates that CmAPX27 exerts a key function in melon's tolerance to salt stress. Generally, CmAPX27 could be a target in molecular breeding efforts aimed at improving the salt tolerance of melon; further studies of CmAPX27 could unveil novel physiological mechanisms through which antioxidant enzymes mitigate the deleterious effects of ROS stress.

Comparative toxicity assessment of individual, binary and ternary mixtures of SiO2, Fe3O4, and ZnO nanoparticles in freshwater microalgae, Scenedesmus obliquus: Exploring the role of dissolved ions

Metal oxide nanoparticles (NPs) are considered among the most prevalent engineered nanomaterials. To have a deeper understanding of the mode of action of multiple metal oxide nanoparticles in mixtures, we have used a unicellular freshwater microalga Scenedesmus obliquus as a model organism. The toxicity of silicon dioxide (SiO2), iron oxide (Fe3O4), and zinc oxide (ZnO) NPs was studied individually as well as in their binary (SiO2 + Fe3O4, Fe3O4 + ZnO, and ZnO + SiO2) and ternary (SiO2 + Fe3O4 + ZnO) combinations. The effects of metal ions from ZnO and Fe3O4 were investigated as well. The results observed from the study, showed that a significant amount of toxicity was contributed by the dissolved ions in the mixtures of the nanoparticles. Decreases in the cell viability, ROS generation, lipid peroxidation, antioxidant enzyme activity, and photosynthetic efficiency were analyzed. Among all the individual particles, ZnO NPs showed the maximum effects and increased the toxicities of the binary mixtures. The binary and ternary mixtures of the NPs clearly showed increased toxic effects in comparison with the individual entities. However, the ternary combination had lesser toxic effects than the binary combination of Fe3O4 + ZnO. The decline in cell viability and photosynthetic efficiency were strongly correlated with various oxidative stress biomarkers emphasizing the crucial role of reactive oxygen species in inducing the toxic effects. The findings from this study highlight the importance of evaluating the combinatorial effects of various metal oxide NPs as part of a comprehensive ecotoxicity assessment in freshwater microalgae.

Differential Antioxidant Response to Supplemental UV-B Irradiation and Sunlight in Three Basil Varieties

Three basil plant varieties (Ocimum basilicum var. Genovese, Ocimum × citriodorum, and Ocimum basilicum var. purpurascens) were grown under moderate light (about 300 µmol photons m-2 s-1) in a glasshouse or growth chamber and then either transferred to an open field (average daily dose: 29.2 kJ m-2 d-1) or additionally exposed to UV-B irradiation in a growth chamber (29.16 kJ m-2 d-1), to reveal the variety-specific and light-specific acclimation responses. Total antioxidant capacity (TAC), phenolic profile, ascorbate content, and class III peroxidase (POD) activity were used to determine the antioxidant status of leaves under all four light regimes. Exposure to high solar irradiation at the open field resulted in an increase in TAC, total hydroxycinnamic acids (HCAs, especially caffeic acid), flavonoids, and epidermal UV-absorbing substances in all three varieties, as well as a two-fold increase in the leaf dry/fresh weight ratio. The supplemental UV-B irradiation induced preferential accumulation of HCAs (rosmarinic acid) over flavonoids, increased TAC and POD activity, but decreased the ascorbate content in the leaves, and inhibited the accumulation of epidermal flavonoids in all basil varieties. Furthermore, characteristic leaf curling and UV-B-induced inhibition of plant growth were observed in all basil varieties, while a pro-oxidant effect of UV-B was indicated with H2O2 accumulation in the leaves and spotty leaf browning. The extent of these morphological changes, and oxidative damage depended on the basil cultivar, implies a genotype-specific tolerance mechanism to high doses of UV-B irradiation.

Transcriptomic and genetic approaches reveal that low-light-induced disease susceptibility is related to cellular oxidative stress in tomato

The impact of low light intensities on plant disease outbreaks represents a major challenge for global crop security, as it frequently results in significant yield losses. However, the underlying mechanisms of the effect of low light on plant defense are still poorly understood. Here, using an RNA-seq approach, we found that the susceptibility of tomato to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) under low light was associated with the oxidation-reduction process. Low light conditions exacerbated Pst DC3000-induced reactive oxygen species (ROS) accumulation and protein oxidation. Analysis of gene expression and enzyme activity of ascorbate peroxidase 2 (APX2) and other antioxidant enzymes revealed that these defense responses were significantly induced by Pst DC3000 inoculation under normal light, whereas these genes and their associated enzyme activities were not responsive to pathogen inoculation under low light. Additionally, the reduced ascorbate to dehydroascorbate (AsA/DHA) ratio was lower under low light compared with normal light conditions upon Pst DC3000 inoculation. Furthermore, the apx2 mutants generated by a CRISPR-Cas9 gene-editing approach were more susceptible to Pst DC3000 under low light conditions. Notably, this increased susceptibility could be significantly reduced by exogenous AsA treatment. Collectively, our findings suggest that low-light-induced disease susceptibility is associated with increased cellular oxidative stress in tomato plants. This study sheds light on the intricate relationship between light conditions, oxidative stress, and plant defense responses, and may pave the way for improved crop protection strategies in low light environments.