Understanding oxidative stress and antioxidant functions to enhance photosynthesis

Silicon nutrition stimulates Salt-Overly Sensitive (SOS) pathway to enhance salinity stress tolerance and yield in rice

In rice (Oryza sativa), Si nutrition is known to improve salinity tolerance; however, limited efforts have been made to elucidate the underlying mechanism. Salt-Overly Sensitive (SOS) pathway contributes to salinity tolerance in plants in a major way which works primarily through Na⁺ exclusion from the cytosol. SOS1, a vital component of SOS pathway is a Na⁺/H⁺ antiporter that maintains ion homeostasis. In this study, we evaluated the effect of overexpression of Oryza sativa SOS1 (OsSOS1) in tobacco (cv. Petit Havana) and rice (cv. IR64) for modulating its response towards salinity further exploring its correlation with Si nutrition. OsSOS1 transgenic tobacco plants showed enhanced tolerance to salinity as evident by its high chlorophyll content and maintaining favorable ion homeostasis under salinity stress. Similarly, transgenic rice overexpressing OsSOS1 also showed improved salinity stress tolerance as shown by higher seed germination percentage, seedling survival and low Na⁺ accumulation under salinity stress. At their mature stage, compared with the non-transgenic plants, the transgenic rice plants showed better growth and maintained better photosynthetic efficiency with reduced chlorophyll loss under stress. Also, roots of transgenic rice plants showed reduced accumulation of Na⁺ leading to reduced oxidative damage and cell death under salinity stress which ultimately resulted in improved agronomic traits such as higher number of panicles and fertile spikelets per panicle. Si nutrition was found to improve the growth of salinity stressed OsSOS1 rice by upregulating the expression of Si transporters (Lsi1 and Lsi2) that leads to more uptake and accumulation of Si in the rice shoots. Metabolite profiling showed better stress regulatory machinery in the transgenic rice, since they maintained higher abundance of most of the osmolytes and free amino acids.

Exogenous Antioxidants Enhance Seedling Growth and Yield of Artificially Aged Cabbage and Lettuce Seeds

Aged seeds exhibit compromised vigour in terms of germination, seedling emergence and growth, but this can to some extent be alleviated by invigoration treatments before sowing. This study aimed to investigate ageing rates and patterns in cabbage (Brassica oleraceae) and lettuce (Lactuca sativa) seeds and whether the beneficial effects of invigorating aged seeds with exogenous antioxidants translate to enhanced seedling performance. Seeds were artificially aged to 25% viability before soaking in 0.4 mM glycerol, 0.6 mM GSH and 0.2 mM trolox for cabbage, and 0.6 mM glycerol, GSH and trolox for lettuce; deionised water served as a control. After 14 days of sowing, seedling emergence percentage, mean emergence time, mean daily emergence, and time taken to 25% emergence were computed. Seedling vigour index, root and shoot dry weight, root:shoot ratio, leaf area, leaf area ratio, and leaf chlorophyll content were assessed 6 weeks after sowing. Furthermore, the photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), and chlorophyll fluorescence were measured 6 weeks after sowing. Notably, ageing resulted in the loss of seed vigour and viability at higher rates in lettuce than cabbage. Seed pretreatment with glycerol promoted seedling growth in both species and shoot dry weight in lettuce, while glycerol and GSH enhanced Pn, Gs and E in lettuce. Trolox also enhanced Pn and E in lettuce. The beneficial effects of the antioxidant treatments are thought to be associated with the protection of photosystems from oxidative stress and/or stimulation of enzymes involved in photosynthesis, possibly through an enhanced antioxidant defence system during the early development stages when seedlings are particularly vulnerable to stress.

The d-mannose/l-galactose pathway is the dominant ascorbate biosynthetic route in the moss Physcomitrium patens

Ascorbate is an abundant and indispensable redox compound in plants. Genetic and biochemical studies have established the d-mannose/l-galactose (d-Man/l-Gal) pathway as the predominant ascorbate biosynthetic pathway in streptophytes, while the d-galacturonate (d-GalUA) pathway is found in prasinophytes and euglenoids. Based on the presence of the complete set of genes encoding enzymes involved in the d-Man/l-Gal pathway and an orthologous gene encoding aldonolactonase (ALase) - a key enzyme for the d-GalUA pathway - Physcomitrium patens may possess both pathways. Here, we have characterized the moss ALase as a functional lactonase and evaluated the ascorbate biosynthesis capability of the two pathways using knockout mutants. Physcomitrium patens expresses two ALase paralogs, namely PpALase1 and PpALase2. Kinetic analyses with recombinant enzymes indicated that PpALase1 is a functional enzyme catalyzing the conversion of l-galactonic acid to the final precursor l-galactono-1,4-lactone and that it also reacts with dehydroascorbate as a substrate. Interestingly, mutants lacking PpALase1 (Δal1) showed 1.2-fold higher total ascorbate content than the wild type, and their dehydroascorbate content was increased by 50% compared with that of the wild type. In contrast, the total ascorbate content of mutants lacking PpVTC2-1 (Δvtc2-1) or PpVTC2-2 (Δvtc2-2), which encode the rate-limiting enzyme GDP-l-Gal phosphorylase in the d-Man/l-Gal pathway, was markedly decreased to 46 and 17%, respectively, compared with that of the wild type. Taken together, the dominant ascorbate biosynthetic pathway in P. patens is the d-Man/l-Gal pathway, not the d-GalUA pathway, and PpALase1 may play a significant role in ascorbate metabolism by facilitating dehydroascorbate degradation rather than ascorbate biosynthesis.

Photoprotection of Arabidopsis leaves under short-term high light treatment: The antioxidant capacity is more important than the anthocyanin shielding effect

Photoprotection strategies that have evolved in plants to cope with high light (HL) stress provide plants with the ability to resist HL. However, it has not been clearly confirmed which photoprotection strategy is the major HL resistance mechanism. To reveal the major photoprotection mechanism against short-term high light (STHL), the physiological and biochemical responses of three Arabidopsis mutants (Col, chi and ans) under STHL were analyzed in this study. After STHL treatment, the most serious photosynthetic pigment damage was observed in chi plants. At the same time, the degrees of membrane and Rubisco damage in chi was the highest, followed by Col, and ans was the smallest. The results showed that ans with high antioxidant capacity showed higher resistance to STHL treatment than Col containing anthocyanins, while chi with no anthocyanin accumulation and small antioxidant capacity had the lowest resistance. In addition, the gene expression results showed that plants tend to synthesize anthocyanin precursor flavonoids with antioxidant capacity under STHL stress. To further determine the major mechanism of photoprotection under STHL, we also analyzed Arabidopsis lines (Col, CHS1, CHS2 and tt4) that had the same anthocyanin content but different antioxidant capacities. It was found that CHS2 with high antioxidant capacity had higher cell viability, smaller maximal quantum yield of PSII photochemistry (F_v/F_m) reduction and less reactive oxygen species (ROS) accumulation under HL treatment of their mesophyll protoplasts. Therefore, the antioxidant capacity provided by antioxidant substances was the major mechanism of plant photoprotection under STHL treatment.

Toward the Design of Potato Tolerant to Abiotic Stress

Potato is a major global crop that has an important role to play in food security, reducing poverty and improving human nutrition. Productivity in potato however is limited in many environments by its sensitivity to abiotic stresses such as elevated temperature, drought, frost, and salinity. In this chapter we focus on the effects of elevated temperature on potato yields as high temperature is the most important uncontrollable factor affecting growth and yield of potato. We describe some of the physiological impacts of elevated temperature and review recent findings about response mechanisms. We describe genetic approaches that could be used to identify allelic variants of genes that may be useful to breed for increased climate resilience, an approach that could be deployed with recent advances in potato breeding.

Opportunities for Improving Waterlogging Tolerance in Cereal Crops-Physiological Traits and Genetic Mechanisms

Waterlogging occurs when soil is saturated with water, leading to anaerobic conditions in the root zone of plants. Climate change is increasing the frequency of waterlogging events, resulting in considerable crop losses. Plants respond to waterlogging stress by adventitious root growth, aerenchyma formation, energy metabolism, and phytohormone signalling. Genotypes differ in biomass reduction, photosynthesis rate, adventitious roots development, and aerenchyma formation in response to waterlogging. We reviewed the detrimental effects of waterlogging on physiological and genetic mechanisms in four major cereal crops (rice, maize, wheat, and barley). The review covers current knowledge on waterlogging tolerance mechanism, genes, and quantitative trait loci (QTL) associated with waterlogging tolerance-related traits, the conventional and modern breeding methods used in developing waterlogging tolerant germplasm. Lastly, we describe candidate genes controlling waterlogging tolerance identified in model plants Arabidopsis and rice to identify homologous genes in the less waterlogging-tolerant maize, wheat, and barley.

Transcriptomic analyses of cacao flavonoids produced in photobioreactors

BACKGROUND

Theobroma cacao is a major source of flavonoids such as catechins and their monomers proanthocyanidins (PAs), widely studied for their potential benefits in cardiovascular diseases. Light has been shown to promote plant secondary metabolite production in vitro. In this study, cacao cells cultured in 7.5 L stirred tank photobioreactors (STPs) were exposed to a change of white to blue LED lights for 28 days (d).

RESULTS

Transcriptomic analyses were performed in three time points comparing changing expression patterns, after cell exposure to white light (d0-VS-d14), after a shift from white to blue light (d14-VS-d15), and after an extended period of blue light for the following 15 days (d15-VS-d28). Under white light, there was enrichment in metabolic pathways associated with cell growth (carbon, glycolysis, and amino acid biosynthesis) accompanied by a significant increase in the PAs content. In the shift to blue light, further increase in PAs content was observed concomitantly with the significant expression of TWO-COMPONENT RESPONSE REGULATOR genes involved in the early stress responses via circadian clock and hormone pathways. Under blue light exposure, we observed a depletion of PAs content associated with ROS-mediated stress pathways.

CONCLUSIONS

Light effects on large-scale cell cultures in photobioreactors are complex and pleiotropic; however, we have been able to identify key regulatory players upstream cacao flavonoid biosynthesis in STPs, including TWO-COMPONENT SYSTEM and ROS-signaling genes. The crosstalk between flavonoid biosynthesis and regulatory networks led to understand the dynamics of flavonoid production and degradation in response to light-driven ROS signals. This can be used to optimize the time, and the yield of in vitro targeted metabolites in large-scale culture systems.

Phytochemical Constituents and Allelopathic Potential of Parthenium hysterophorus L. in Comparison to Commercial Herbicides to Control Weeds

The allelopathic effect of various concentrations (0, 6.25, 12.5, 50 and 100 g L^-1) of Parthenium hysterophorus methanol extract on Cyperus iria was investigated under laboratory and glasshouse conditions. No seed germination was recorded in the laboratory when P. hysterophorus extract was applied at 50 g L^-1. In the glasshouse, C. iria was mostly injured by P. hysterophorus extract at 100 g L^-1. The phytochemical constituents of the methanol extract of P. hysterophorus were analyzed by LC-ESI-QTOF-MS=MS. The results indicated the presence of phenolic compounds, terpenoids, alkaloids, amino acids, fatty acids, piperazines, benzofuran, indole, amines, azoles, sulfonic acid and other unknown compounds in P. hysterophorus methanol extract. A comparative study was also conducted between P. hysterophorus extract (20, 40 and 80 g L^-1) with a synthetic herbicide (glyphosate and glufosinate ammonium at 2 L ha^-1) as a positive control and no treatment (negative control) on Ageratumconyzoides, Oryzasativa and C. iria. The growth and biomass of test weeds were remarkably inhibited by P. hysterophorus extract. Nevertheless, no significant difference was obtained when P. hysterophorus extract (80 g L^-1) and synthetic herbicides (glyphosate and glufosinate ammonium) were applied on A.conyzoides.

The interactive effect of pH variation and cadmium stress on wheat (Triticum aestivum L.) growth, physiological and biochemical parameters

Anthropogenic activities such as mining, manufacturing, and application of fertilizers release substantial quantities of cadmium (Cd) into the environment. In the natural environment, varying pH may play an important role in the absorption and accumulation of Cd in plants, which can cause toxicity and increase the risk to humans. We conducted a hydroponic experiment to examine the impact of pH on cadmium (Cd) solubility and bioavailability in winter wheat (Triticum aestivum L.) under controlled environmental conditions. The results showed that Cd concentration was significantly reduced in wheat with an increase in pH from 5 to 7, while it was dramatically increased at pH ranging from 7 to 9. However, in both cases, a significant reduction in physiological traits was observed. The addition of Cd (20, 50, and 200 μmol L^-1) at all pH levels caused a substantial decline in wheat growth, chlorophyll and carotenoids contents, nutrient availability, while elevated cell membrane damage was observed in terms of electrolytic leakage (EL), osmoprotectants, and antioxidants activity. In our findings, the negative effects of acidic pH (5) on wheat growth and development were more pronounced in the presence of Cd toxicities. For instance, Cd concentration with 20, 50, and 200 μmol L^-1 at acidic pH (5) reduced shoot dry biomass by 45%, 53%, and 79%, total chlorophyll contents by 26%, 41%, 56% while increased CAT activity in shoot by 109%, 175%, and 221%, SOD activity in shoot by 122%, 135%, and 167%, POD activity in shoot by 137%, 250%, and 265%, MDA contents in shoot by 51%, 83%, and 150%, H₂O₂ contents in shoot by 175%, 219%, and 292%, EL in shoot by 108%, 165%, and 230%, proline contents in shoot by 235%, 280%, and 393%, respectively as compared to neutral pH without Cd toxicities. On the other hand, neutral pH with Cd toxicities alleviated the negative effects of Cd toxicity on wheat plants by limiting Cd uptake, reduced reactive oxygen species (ROS) formation, and increased nutrient availability. In conclusion, neutral pH minimized the adverse effects of Cd stress by minimizing its uptake and accumulation in wheat plants.

Transient photoinhibition and photo-oxidative stress as an integral part of stress acclimation and plant development in a dioecious tree adapted to Mediterranean ecosystems

Mastic trees (Pistacia lentiscus L.) are dioecious perennial plants that are highly adapted to Mediterranean climates but display a high sensitivity to winter periods. In order to understand how sex, leaf phenology and ecological context could condition sensitivity to winter and associated mechanisms to acclimate to these conditions, photoinhibition and photo-oxidative stress markers were examined in mastic trees (P. lentiscus) from a natural population growing in the Garraf Natural Park for a consecutive 12-month period (seasonal study), as well as in three populations naturally growing in the Montseny Natural Park, including the highest altitudes described for this species, during winter (altitudinal study). Results from these studies indicate that both the winter period and higher elevation influenced the degree of photoinhibition, but this was not conditioned by sex. In fact, winter photoinhibition occurred transiently even though it was accompanied by chlorophyll loss and malondialdehyde contents. Stress acclimation was achieved through biochemical adjustments in chloroplasts, characterized by anthocyanin shielding, increased de-epoxidation state of the xanthophyll cycle as well as tocopherol accumulation, and phenological adaptations, the latter allowing a complete resetting of the physiological performance of leaves. Moreover, although females showed higher lipid peroxidation than males during the coldest winter months, at the highest elevation and during flowering in spring, this oxidative stress was mild and transient with no negative consequences for the physiology of plants. It is concluded that evergreen mastic trees acclimate to winter conditions and higher elevations by activation of antioxidant defenses together with phenological adjustments, altogether playing a crucial role in plant survival. Sexual dimorphism in mastic trees appears as a relevant factor when considering sensitivity to photo-oxidative stress in winter and altitudinal conditions.

Comparative toxicity of rod-shaped nano-CeO2 and nano-CePO4 to lettuce

The influence of morphology on the biological effects of nanomaterials (NMs) has not been well understood. In the present study, we compared the phytotoxicity of rod-shaped nano-cerium dioxide (R-CeO2) and nano-cerium phosphate (R-CePO4) to lettuce plants. The results showed that R-CeO2 significantly inhibited the root elongation of lettuce, induced oxidative damages, and caused cell death, while R-CePO4 was nontoxic to lettuce. The different distribution and speciation of Ce in plant tissues were determined by transmission electron microscopy (TEM) and X-ray absorption near edge spectroscopy (XANES) combined with linear combination fitting (LCF). The results showed that in the R-CeO2 group, part of Ce was transformed from Ce(IV) to Ce(III), while only Ce(III) was present in the R-CePO4 group. When interacting with plants, R-CeO2 is easier to be dissolved and transformed than R-CePO4, which might be the reason for their different phytotoxicity. Although both are Ce-based NMs and have the same morphology, the toxicity of R-CeO2 seems to come from the released Ce3+ ions rather than its shape. This research emphasizes the importance of chemical composition and reactivity of NMs to their toxicological effects.

Salinity induced alterations in photosynthetic and oxidative regulation are ameliorated as a function of salt secretion

Ion secretion facilitates recretohalophytes to tolerate saline and drought conditions but its relative contribution to the survival of many species remains poorly understood. Tamarix chinensis has high potential for restoration of saline deteriorated lands. The water management and high salt tolerance of the plant have highlighted the need to determine the strategies that govern these mechanisms. Here we report the selectivity of this halophyte to transport, utilize, and secrete different cations and anions under various NaCl (0, 100, 200 and 400 mM) concentrations. Plant growth, photosynthesis and antioxidant defense responses were also determined to relate them with the function of ion secretion. Results reflected two different sets of strategies adopted by plants to survive low and high salinities. Exposure to highly saline conditions caused reduction in photosynthesis due to stomatal and biochemical limitations. The decreased content of photosynthetic pigments exposed plants to excessive light energy that accelerated production of ROS (i.e., hydrogen peroxide H₂O₂) and caused damage to cellular membranes. The increased activities of anti-oxidative enzymes (superoxide-dismutase, catalase, ascorbate-peroxidase, and glutathione-reductase) were insufficient to detoxify H₂O₂. In contrast, plants treated with low salinity did not face stomatal limitations while the photosynthetic pigments increased. As no damage to membranes was detected, the increased content of H₂O₂ was postulated for its messenger role. The assimilation of essential nutrients was affected due to increased content of toxic ions (Na⁺ and Cl^-) in the growing medium and within the plants. However, the ability to regulate K⁺ facilitated plants to improve water use efficiency under hyper-osmotic environment. The removal of toxic ions from the photosynthesizing tissues demands high energy, which was evident in the compromised growth of plants. This study offers a window to physiological mechanisms, e.g., potassium retention that ensure salt secretion as a beneficial strategy for prolonged survival of T. chinensis.

Distribution of the Water-Soluble Astaxanthin Binding Carotenoprotein (AstaP) in Scenedesmaceae

Photooxidative stress-inducible water-soluble astaxanthin-binding proteins, designated as AstaP, were identified in two Scenedesmaceae strains, Coelastrella astaxanthina Ki-4 and Scenedesmus obtusus Oki-4N; both strains were isolated under high light conditions. These AstaPs are classified as a novel family of carotenoprotein and are useful for providing valuable astaxanthin in water-soluble form; however, the distribution of AstaP orthologs in other microalgae remains unknown. Here, we examined the distribution of AstaP orthologs in the family Scenedesmaceae with two model microalgae, Chlamydomonas reinhardtii and Chlorella variabilis. The expression of AstaP orthologs under photooxidative stress conditions was detected in cell extracts of Scenedesmaceae strains, but not in model algal strains. Aqueous orange proteins produced by Scenedesmaceae strains were shown to bind astaxanthin. The protein from Scenedesmus costatus SAG 46.88 was purified. It was named ScosAstaP and found to bind astaxanthin. The deduced amino acid sequence from a gene encoding ScosAstaP showed 62% identity to Ki-4 AstaP. The expression of the genes encoding AstaP orthologs was shown to be inducible under photooxidative stress conditions; however, the production amounts of AstaP orthologs were estimated to be approximately 5 to 10 times lower than that of Ki-4 and Oki-4N.

Physiological and Biochemical Responses of Ageratum conyzoides, Oryza sativa f. spontanea (Weedy Rice) and Cyperus iria to Parthenium hysterophorus Methanol Extract

The current study was designed to investigate the effect of Parthenium hysterophorus L. methanol extract on Ageratum conyzoides L., Oryza sativa f. spontanea (weedy rice) and Cyperus iria L. in glasshouse condition. Here, Parthenium hysterophorus methanol extract at 20, 40, and 60 g L⁻¹ concentrations was applied on the test species to examine their physiological and biochemical responses at 6, 24, 48 and 72 h after spraying (HAS). The phytotoxicity of P. hysterophorus was strong on A. conyzoides compared to weedy rice and Cyperus iria at different concentrations and exposure times. There was a reduction in photosynthesis rate, stomatal conductance, transpiration, chlorophyll content and carotenoid content when plants were treated with P. hysterophorus extract concentrations. Exposure to P. hysterophorus (60 g L⁻¹) at 24 HAS increased malondialdehyde (MDA) and proline content by 152% and 130%, respectively, in A. conyzoides compared with control. The activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) were also increased in the presence of P. hysterophorus extract. Present findings confirm that the methanol extract of P. hysterophorus can disrupt the physiological and biochemical mechanism of target weeds and could be used as an alternative to chemical herbicides.

Application of garlic allelochemicals improves growth and induces defense responses in eggplant (Solanum melongena) against Verticillium dahliae

Aqueous garlic extracts (AGE) and garlic allelochemical diallyl disulfide (DADS) have been recently reported to bear bioactive properties to stimulate plant growth and development and alter defense-related physiology. We, therefore, performed a bioassay to study these chemicals as possible biostimulants for defense against Verticillium dahliae in eggplant seedlings. AGE and DADS were applied as a foliar application to the eggplants and samples were collected before and after pathogen inoculation at various intervals to analyze the defense mechanism. The obtained data revealed that with the application of AGE and DADS, the seedlings showed responses including activation of antioxidant enzymes, an abundance of chlorophyll contents, alteration of photosynthesis system, and accumulation of plant hormones compared to the control plants. Furthermore, the microscopic analysis of the AGE or DADS treated plants showed high variability in pathogen density within the root crown at 28 days post-inoculation. The low abundance of reactive oxygen species was noticed in AGE or DADS treated plants, which indicates that the plants were able to successfully encounter pathogen attacks. The AGE and DADS treated plants exhibited a lower disease severity index (32.4% and 24.8% vs 87.1% in controls), indicating successful defense against Verticillium infection. Our results were therefore among the first to address the biostimulatory effects of AGE or DADS to induce resistance in eggplant seedlings against V. dahliae and may be used to establish preparation for garlic-derived bioactive compounds to improve growth and defense responses of eggplants under-protected horticultural situations such as glasshouse or plastic tunnels system.

Peroxidase activity and operation of photo-protective component of NPQ play key roles in drought tolerance of mung bean [Vigna radiata (L.) Wilcziek]

Developing drought-tolerant cultivars is mainly restricted due to poor knowledge of the mechanism behind drought tolerance. In the present work, available germplasm of Vigna radiata (mung bean) was screened for drought tolerance using multiple agronomic and physiological parameters and used to selected one drought-tolerant (NM-13-1) and one drought-sensitive (NM-54) cultivar for further studies. Plant water status and PSII activity were found to be potential physiological discriminating traits. Changes in PSII and PSI activity, accumulation of proline, oxidative damage, and antioxidants were further assessed in selected drought-sensitive and drought-tolerant cultivars. Drought stress reduced PSII efficiency and electron transport in both mung bean cultivars. Drought increased NPQ and Y(NPQ), a greater increase in NPQ and Y(NPQ) was found in the drought-tolerant cv NM-13-1, indicating that the drought-tolerant cultivar managed over-excitation of PSII by safe heat dissipation via photo-protective component of NPQ. A decrease in PSI efficiency with an increase in donor end limitation of PSI in both mung bean cultivars further confirmed that the electron transport through PSII became down-regulated. However, the drought-sensitive cv. NM-54 had poor ability to manage over-excitation of PSII through buildup of Y(NPQ) thereby causing greater oxidative stress. Mung bean cultivars counteracted oxidative stress by accumulation of proline and increasing POD activities. Drought-tolerant cv. NM-13-1 had higher proline accumulation and antioxidant potential than in the drought-sensitive cultivar. Overall, drought tolerance in the mung bean cultivars can be related to plant water status, PSII activity, Y(NPQ), and POD activity, which can be effectively used for selecting mung bean cultivars for drought tolerance.

Glucose-induced response on photosynthetic efficiency, ROS homeostasis, and antioxidative defense system in maintaining carbohydrate and ion metabolism in Indian mustard (Brassica juncea L.) under salt-mediated oxidative stress

In plants, glucose (Glc) acts as a crucial signaling molecule in mediating metabolism, growth, stress tolerance mechanism, etc. However, little is known about Glc supplementation in salinity tolerance. This experiment was designed to study the ameliorative effect of Glc in mustard under salt stress. The seeds were soaked in three concentrations of NaCl (0, 50, or 100 mM) for 8 h and then treated with four concentrations of Glc (0, 2, 4, or 8%) as foliar spray for 5 days at 25-day stage. The plants were harvested at three growth stages (30, 45, and 60) for examining morpho-physiological and proteomic studies. Glc application as foliar spray increases growth, photosynthesis, and antioxidative enzyme activities in NaCl-treated plants. Glc applied in plants also showed reduction in superoxide anion, hydrogen peroxide, and malondialdehyde content under salt stress. Amongst all doses of Glc, spray of 4% Glc proved best in alleviating the harmful effects of salinity.

The AaCBF4-AaBAM3.1 module enhances freezing tolerance of kiwifruit (Actinidia arguta)

Beta-amylase (BAM) plays an important role in plant resistance to cold stress. However, the specific role of the BAM gene in freezing tolerance is poorly understood. In this study, we demonstrated that a cold-responsive gene module was involved in the freezing tolerance of kiwifruit. In this module, the expression of AaBAM3.1, which encodes a functional protein, was induced by cold stress. AaBAM3.1-overexpressing kiwifruit lines showed increased freezing tolerance, and the heterologous overexpression of AaBAM3.1 in Arabidopsis thaliana resulted in a similar phenotype. The results of promoter GUS activity and cis-element analyses predicted AaCBF4 to be an upstream transcription factor that could regulate AaBAM3.1 expression. Further investigation of protein-DNA interactions by using yeast one-hybrid, GUS coexpression, and dual luciferase reporter assays confirmed that AaCBF4 directly regulated AaBAM3.1 expression. In addition, the expression of both AaBAM3.1 and AaCBF4 in kiwifruit responded positively to cold stress. Hence, we conclude that the AaCBF-AaBAM module is involved in the positive regulation of the freezing tolerance of kiwifruit.

Metabolic Profile Discriminates and Predicts Arabidopsis Susceptibility to Virus under Field Conditions

As obligatory parasites, plant viruses alter host cellular metabolism. There is a lack of information on the variability of virus-induced metabolic responses among genetically diverse plants in a natural context with daily changing conditions. To decipher the metabolic landscape of plant-virus interactions in a natural setting, twenty-six and ten accessions of Arabidopsis thaliana were inoculated with Turnip mosaic virus (TuMV), in two field experiments over 2 years. The accessions were measured for viral accumulation, above-ground biomass, targeted and untargeted metabolic profiles. The phenotypes of the accessions ranged from susceptibility to resistance. Susceptible and resistant accessions were shown to have different metabolic routes after inoculation. Susceptible genotypes accumulate primary and secondary metabolites upon infection, at the cost of hindered growth. Twenty-one metabolic signatures significantly accumulated in resistant accessions whereas they maintained their growth as mock-inoculated plants without biomass penalty. Metabolic content was demonstrated to discriminate and be highly predictive of the susceptibility of inoculated Arabidopsis. This study is the first to describe the metabolic landscape of plant-virus interactions in a natural setting and its predictive link to susceptibility. It provides new insights on plant-virus interactions. In this undomesticated species and in ecologically realistic conditions, growth and resistance are in a permanent conversation.

Zinc Oxide Nanoparticles and Zinc Sulfate Impact Physiological Parameters and Boosts Lipid Peroxidation in Soil Grown Coriander Plants (Coriandrum sativum)

The objective of this study was to determine the oxidative stress and the physiological and antioxidant responses of coriander plants (Coriandrum sativum) grown for 58 days in soil with zinc oxide nanoparticles (ZnO NPs) and zinc sulfate (ZnSO4) at concentrations of 0, 100, 200, 300, and 400 mg of Zn/kg of soil. The results revealed that all Zn compounds increased the total chlorophyll content (CHLt) by at least 45%, compared to the control group; however, with 400 mg/kg of ZnSO4, chlorophyll accumulation decreased by 34.6%. Zn determination by induction-plasma-coupled atomic emission spectrometry (ICP-AES) showed that Zn absorption in roots and shoots occurred in plants exposed to ZnSO4 at all concentrations, which resulted in high levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Only at 400 mg/kg of ZnSO4, a 78.6% decrease in the MDA levels was observed. According to the results, the ZnSO4 treatments were more effective than the ZnO NPs to increase the antioxidant activity of catalase (CAT), ascorbate peroxidase (APX), and peroxidases (POD). The results corroborate that phytotoxicity was higher in plants subjected to ZnSO4 compared to treatments with ZnO NPs, which suggests that the toxicity was due to Zn accumulation in the tissues by absorbing dissolved Zn++ ions.

Cellular oxidative stress in programmed cell death: focusing on chloroplastic 1O2 and mitochondrial cytochrome-c release

The programmed cell death (PCD) occurs when the targeted cells have fulfilled their task or under conditions as oxidative stress generated by ROS species. Thus, plants have to deal with the singlet oxygen ¹O₂ produced in chloroplasts. ¹O₂ is unlikely to act as a primary retrograde signal owing to its high reactivity and short half-life. In addition to its high toxicity, the ¹O₂ generated under an excess or low excitation energy might also act as a highly versatile signal triggering chloroplast-to-nucleus retrograde signaling (ChNRS) and nuclear reprogramming or cell death. Molecular and biochemical studies with the flu mutant, which accumulates protochlorophyllide in the dark, demonstrated that chloroplastic ¹O₂-driven EXECUTER-1 (EX1) and EX2 proteins are involved in the ¹O₂-dependent response. Both EX1 and EX2 are necessary for full suppression of ¹O₂-induced gene expression. That is, EXECUTER proteolysis via the ATP-dependent zinc protease (FtsH) is an integral part of ¹O₂-triggered retrograde signaling. The existence of at least two independent ChNRS involving EX1 and β-cyclocitral, and dihydroactinidiolide and OXI1, respectively, seem clear. Besides, this update also focuses on plant PCD and its relation with mitochondrial cytochrome-c (Cytc) release to cytosol. Changes in the dynamics and morphology of mitochondria were shown during the onset of cell death. The mitochondrial damage and translocation of Cytc may be one of the major causes of PCD triggering. Together, this current overview illustrates the complexity of the cellular response to oxidative stress development. A puzzle with the majority of its pieces still not placed.

Ozone critical levels for (semi-)natural vegetation dominated by perennial grassland species

New critical levels for ozone based on accumulated flux through stomata (phytotoxic ozone dose, POD), for temperate perennial grassland (semi-)natural vegetation, have been agreed for use within the Convention on Long-Range Transboundary Air Pollution. These were based on data from several experiments conducted under naturally fluctuating environmental conditions that were combined and analysed to give linear dose-response relationships. Dose-response functions and flux-based critical levels were derived based on biomass and flower number. These parameters showed a statistically significant decline with increasing accumulated stomatal ozone flux. The functions and critical levels derived are based on sensitive species and can be used for risk assessments of the damaging effect of ozone on temperate vegetation communities dominated by perennial grassland species. The critical level based on flower number was lower than that for biomass, representing the greater sensitivity of flower number to ozone pollution.

Identification and Characterization of the APX Gene Family and Its Expression Pattern under Phytohormone Treatment and Abiotic Stress in Populus trichocarpa

Ascorbate peroxidase (APX) is a member of class I of the heme-containing peroxidase family. The enzyme plays important roles in scavenging reactive oxygen species for protection against oxidative damage and maintaining normal plant growth and development, as well as in biotic stress responses. In this study, we identified 11 APX genes in the Populus trichocarpa genome using bioinformatic methods. Phylogenetic analysis revealed that the PtrAPX proteins were classifiable into three clades and the members of each clade shared similar gene structures and motifs. The PtrAPX genes were distributed on six chromosomes and four segmental-duplicated gene pairs were identified. Promoter cis-elements analysis showed that the majority of PtrAPX genes contained a variety of phytohormone- and abiotic stress-related cis-elements. Tissue-specific expression profiles indicated that the PtrAPX genes primarily function in roots and leaves. Real-time quantitative PCR (RT-qPCR) analysis indicated that PtrAPX transcription was induced in response to drought, salinity, high ammonium concentration, and exogenous abscisic acid treatment. These results provide important information on the phylogenetic relationships and functions of the APX gene family in P. trichocarpa.

Heat Shock Tolerance in Deschampsia antarctica Desv. Cultivated in vitro Is Mediated by Enzymatic and Non-enzymatic Antioxidants

Deschampsia antarctica Desv, is the most successful colonizing species of a cold continent. In recent years due to climate change, the frequency of heat waves has increased in Antarctica, registering anomalous high temperatures during the summer of 2020. However, the populations of D. antarctica are responding positively to these events, increasing in number and size throughout the Antarctic Peninsula. In this work, the physiological and biochemical responses of D. antarctica plants grown in vitro (15 ± 1°C) and plants subjected to two heat shock treatments (23 and 35°C) were evaluated. The results obtained show that D. antarctica grown in vitro is capable of tolerating heat shock treatments; without showing visible damage to its morphology, or changes in its oxidative state and photosynthetic performance. These tolerance responses are primarily mediated by the efficient role of enzymatic and non-enzymatic antioxidant systems that maintain redox balance at higher temperatures. It is postulated that these mechanisms also operate in plants under natural conditions when exposed to environmental stresses.

Interspecific protection against oxidative stress: green algae protect harmful cyanobacteria against hydrogen peroxide

Oceanographic studies have shown that heterotrophic bacteria can protect marine cyanobacteria against oxidative stress caused by hydrogen peroxide (H₂O₂). Could a similar interspecific protection play a role in freshwater ecosystems? In a series of laboratory experiments and two lake treatments, we demonstrate that freshwater cyanobacteria are sensitive to H₂O₂ but can be protected by less‐sensitive species such as green algae. Our laboratory results show that green algae degrade H₂O₂ much faster than cyanobacteria. Consequently, the cyanobacterium Microcystis was able to survive at higher H₂O₂ concentrations in mixtures with the green alga Chlorella than in monoculture. Interestingly, even the lysate of destructed Chlorella was capable to protect Microcystis, indicating a two‐component H₂O₂ degradation system in which Chlorella provided antioxidant enzymes and Microcystis the reductants. The level of interspecific protection provided to Microcystis depended on the density of Chlorella. These findings have implications for the mitigation of toxic cyanobacterial blooms, which threaten the water quality of many eutrophic lakes and reservoirs worldwide. In several lakes, H₂O₂ has been successfully applied to suppress cyanobacterial blooms. Our results demonstrate that high densities of green algae can interfere with these lake treatments, as they may rapidly degrade the added H₂O₂ and thereby protect the bloom‐forming cyanobacteria.

Abiotic Stress and Reactive Oxygen Species: Generation, Signaling, and Defense Mechanisms

Climate change is an invisible, silent killer with calamitous effects on living organisms. As the sessile organism, plants experience a diverse array of abiotic stresses during ontogenesis. The relentless climatic changes amplify the intensity and duration of stresses, making plants dwindle to survive. Plants convert 1-2% of consumed oxygen into reactive oxygen species (ROS), in particular, singlet oxygen (1O2), superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), etc. as a byproduct of aerobic metabolism in different cell organelles such as chloroplast, mitochondria, etc. The regulatory network comprising enzymatic and non-enzymatic antioxidant systems tends to keep the magnitude of ROS within plant cells to a non-damaging level. However, under stress conditions, the production rate of ROS increases exponentially, exceeding the potential of antioxidant scavengers instigating oxidative burst, which affects biomolecules and disturbs cellular redox homeostasis. ROS are similar to a double-edged sword; and, when present below the threshold level, mediate redox signaling pathways that actuate plant growth, development, and acclimatization against stresses. The production of ROS in plant cells displays both detrimental and beneficial effects. However, exact pathways of ROS mediated stress alleviation are yet to be fully elucidated. Therefore, the review deposits information about the status of known sites of production, signaling mechanisms/pathways, effects, and management of ROS within plant cells under stress. In addition, the role played by advancement in modern techniques such as molecular priming, systems biology, phenomics, and crop modeling in preventing oxidative stress, as well as diverting ROS into signaling pathways has been canvassed.

Tomato Bio-Protection Induced by Pseudomonas fluorescens N21.4 Involves ROS Scavenging Enzymes and PRs, without Compromising Plant Growth

Aims: to discover the interrelationship between growth, protection and photosynthesis induced by Pseudomonas fluorescens N21.4 in tomato (Lycopersicum sculentum) challenged with the leaf pathogen Xanthomonas campestris, and to define its priming fingerprint. Methods: Photosynthesis was determined by fluorescence; plant protection was evaluated by relative disease incidence, enzyme activities by specific colorimetric assays and gene expression by qPCR. Changes in Reactive Oxygen Species (ROS) scavenging cycle enzymes and pathogenesis related protein activity and expression were determined as metabolic and genetic markers of induction of systemic resistance. Results: N21.4 significantly protected plants and increased dry weight. Growth increase is supported by significant increases in photochemical quenching together with significant decreases in energy dissipation (Non-Photochemical Quenching, NPQ). Protection was associated with changes in ROS scavenging cycle enzymes, which were significantly increased on N21.4 + pathogen challenged plants, supporting the priming effect. Superoxide Dismutase (SOD) was a good indicator of biotic stress, showing similar levels in pathogen- and N21.4-treated plants. Similarly, the activity of defense-related enzymes, ß-1,3-glucanase and chitinase significantly increased in post-pathogen challenge state; changes in gene expression were not coupled to activity. Conclusions: protection does not compromise plant growth; N21.4 priming fingerprint is defined by enhanced photochemical quenching and decreased energy dissipation, enhanced chlorophylls, primed ROS scavenging cycle enzyme activity, and glucanase and chitinase activity.

Priming with a Seaweed Extract Strongly Improves Drought Tolerance in Arabidopsis

Drought represents a major threat to plants in natural ecosystems and agricultural settings. The biostimulant Super Fifty (SF), produced from the brown alga Ascophyllum nodosum, enables ecologically friendly stress mitigation. We investigated the physiological and whole-genome transcriptome responses of Arabidopsis thaliana to drought stress after a treatment with SF. SF strongly decreased drought-induced damage. Accumulation of reactive oxygen species (ROS), which typically stifle plant growth during drought, was reduced in SF-primed plants. Relative water content remained high in SF-treated plants, whilst ion leakage, a measure of cell damage, was reduced compared to controls. Plant growth requires a functional shoot apical meristem (SAM). Expression of a stress-responsive negative growth regulator, RESPONSIVE TO DESICCATION 26 (RD26), was repressed by SF treatment at the SAM, consistent with the model that SF priming maintains the function of the SAM during drought stress. Accordingly, expression of the cell cycle marker gene HISTONE H4 (HIS4) was maintained at the SAMs of SF-primed plants, revealing active cell cycle progression after SF priming during drought. In accordance with this, CYCP2;1, which promotes meristem cell division, was repressed by drought but enhanced by SF. SF also positively affected stomatal behavior to support the tolerance to drought stress. Collectively, our data show that SF priming mitigates multiple cellular processes that otherwise impair plant growth under drought stress, thereby providing a knowledge basis for future research on crops.

ABA and BAP improve the accumulation of carbohydrates and alter carbon allocation in potato plants at elevated CO2

Elevated CO2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO2 concentration and plant growth regulators (PGRs) on potato (Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants (cvs. Agria and Fontane) to combined application of CO2 levels (400 vs. 800 µmol mol-1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO2. In Agria, the ratio of leaf intercellular to ambient air CO2 concentrations [Ci:Ca] was declined in elevated-CO2-grown plants, which indicated the stomata would become more conservative at higher CO2 levels. On the other hand, the increased Ci:Ca in Fontane showed a stomatal acclimation to higher CO2 concentration. The higher leaf dark respiration of the elevated CO2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO2 on tuber yield and productivity of the potato plants.

Tetraedron minimum, First Reported Member of Hydrodictyaceae to Accumulate Secondary Carotenoids

We isolated a novel strain of the microalga Tetraedron minimum in Iceland from a terrestrial habitat. During long-term cultivation, a dish culture turned orange, indicating the presence of secondary pigments. Thus, we characterized T. minimum for growth and possible carotenoid production in different inorganic media. In a lab-scale photobioreactor, we confirmed that nitrogen starvation in combination with salt stress triggered a secondary carotenoid accumulation. The development of the pigment composition and the antioxidant capacity of the extracts was analyzed throughout the cultivations. The final secondary carotenoid composition was, on average, 61.1% astaxanthin and 38.9% adonixanthin. Moreover, the cells accumulated approx. 83.1% unsaturated fatty acids. This work presents the first report of the formation of secondary carotenoids within the family Hydrodictyaceae (Sphaeropleales, Chlorophyta).

Role of an ancient light-harvesting protein of PSI in light absorption and photoprotection

Diverse algae of the red lineage possess chlorophyll a-binding proteins termed LHCR, comprising the PSI light-harvesting system, which represent an ancient antenna form that evolved in red algae and was acquired through secondary endosymbiosis. However, the function and regulation of LHCR complexes remain obscure. Here we describe isolation of a Nannochloropsis oceanica LHCR mutant, named hlr1, which exhibits a greater tolerance to high-light (HL) stress compared to the wild type. We show that increased tolerance to HL of the mutant can be attributed to alterations in PSI, making it less prone to ROS production, thereby limiting oxidative damage and favoring growth in HL. HLR1 deficiency attenuates PSI light-harvesting capacity and growth of the mutant under light-limiting conditions. We conclude that HLR1, a member of a conserved and broadly distributed clade of LHCR proteins, plays a pivotal role in a dynamic balancing act between photoprotection and efficient light harvesting for photosynthesis.

LHCR proteins are ancient chlorophyll a-binding antennas that evolved in diverse algae of the red lineage. Here Lu et al. characterize a red lineage LHCR mutant and show reduced oxidative damage in high light but attenuated growth under low light, thus demonstrating how LHCR proteins impact the balance between photoprotection and light harvesting.

The 26S Proteasome Regulatory Subunit GmPSMD Promotes Resistance to Phytophthora sojae in Soybean

Phytophthora root rot, caused by Phytophthora sojae is a destructive disease of soybean (Glycine max) worldwide. We previously confirmed that the bHLH transcription factor GmPIB1 (P. sojae-inducible bHLH transcription factor) reduces accumulation of reactive oxygen species (ROS) in cells by inhibiting expression of the peroxidase-related gene GmSPOD thus improving the resistance of hairy roots to P. sojae. To identify proteins interacting with GmPIB1 and assess their participation in the defense response to P. sojae, we obtained transgenic soybean hairy roots overexpressing GmPIB1 by Agrobacterium rhizogenes mediated transformation and examined GmPIB1 protein-protein interactions using immunoprecipitation combined with mass spectrometry. We identified 392 proteins likely interacting with GmPIB1 and selected 20 candidate genes, and only 26S proteasome regulatory subunit GmPSMD (Genbank accession no. XP_014631720) interacted with GmPIB1 in luciferase complementation and pull-down experiments and yeast two-hybrid assays. Overexpression of GmPSMD (GmPSMD-OE) in soybean hairy roots remarkably improved resistance to P. sojae and RNA interference of GmPSMD (GmPSMD -RNAi) increased susceptibility. In addition, accumulation of total ROS and hydrogen peroxide (H₂O₂) in GmPSMD-OE transgenic soybean hairy roots were remarkably lower than those of the control after P. sojae infection. Moreover, in GmPSMD-RNAi transgenic soybean hairy roots, H₂O₂ and the accumulation of total ROS exceeded those of the control. There was no obvious difference in superoxide anion (O₂ ^-) content between control and transgenic hairy roots. Antioxidant enzymes include peroxidase (POD), glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT) are responsible for ROS scavenging in soybean. The activities of these antioxidant enzymes were remarkably higher in GmPSMD-OE transgenic soybean hairy roots than those in control, but were reduced in GmPSMD-RNAi transgenic soybean hairy roots. Moreover, the activity of 26S proteasome in GmPSMD-OE and GmPIB1-OE transgenic soybean hairy roots was significantly higher than that in control and was significantly lower in PSMD-RNAi soybean hairy roots after P. sojae infection. These data suggest that GmPSMD might reduce the production of ROS by improving the activity of antioxidant enzymes such as POD, SOD, GPX, CAT, and GmPSMD plays a significant role in the response of soybean to P. sojae. Our study reveals a valuable mechanism for regulation of the pathogen response by the 26S proteasome in soybean.

Titanium Application Increases Phosphorus Uptake Through Changes in Auxin Content and Root Architecture in Soybean (Glycine Max L.)

Phosphorus (P) is an essential macronutrient needed for plant growth, development, and production. A deficiency of P causes a severe impact on plant development and productivity. Several P-based fertilizers are being used in agriculture but limited uptake of P by the plant is still a challenge to be solved. Titanium (Ti) application increases the nutrient uptake by affecting the root growth; however, the role of Ti in plant biology, specifically its application under low light and phosphorus stress, has never been reported. Therefore, a pot study was planned with foliar application of Ti (in a different concentration ranging from 0 to 1,000 mg L^-1) under different light and P concentrations. The result indicated that under shade and low P conditions the foliar application of Ti in different concentrations significantly improves the plant growth parameters such as root length, root surface area, root dry matter, and shoot dry matters. The increase was observed to be more than 100% in shade and low P stressed soybean root parameter with 500 mg L^-1 of Ti treatment. Ti was observed to improve the plant growth both in high P and low P exposed plants, but the improvement was more obvious in Low P exposed plants. Auxin concentration in stressed and healthy plant roots was observed to be slightly increased with Ti application. Ti application was also observed to decrease rhizosphere soil pH and boosted the antioxidant enzymatic activities with an enhancement in photosynthetic efficiency of soybean plants under shade and P stress. With 500 mg L^-1 of Ti treatment, the photosynthetic rate was observed to improve by 45% under shade and P stressed soybean plants. Thus, this work for the first time indicates a good potential of Ti application in the low light and P deficient agricultural fields for the purpose to improve plant growth and development parameters.

Effects of Propranolol on Growth, Lipids and Energy Metabolism and Oxidative Stress Response of Phaeodactylum tricornutum

Simple Summary

In the past two decades, increasing attention has been directed to investigate the incidence and consequences of pharmaceuticals in the aquatic environment. Propranolol is a non-selective β-adrenoceptor blocker used in large quantities worldwide to treat cardiovascular conditions. Diatoms (model organism) exposed to this compound showed evident signs of oxidative stress, a significant reduction of the autotrophic O₂ production and an increase in the heterotrophic mitochondrial respiration. Additionally, diatoms exposed to propranolol showed a consumption of its storage lipids. In ecological terms this will have cascading impacts in the marine trophic webs, where these organisms are key elements, through a reduction of the water column oxygenation and essential fatty acid availability to the heterotrophic organisms that depend on these primary producers. In ecotoxicological terms, diatoms photochemical and fatty acid traits showed to be potential good biomarkers for toxicity assessment of diatoms exposed to this widespread pharmaceutical compound.

Abstract

Present demographic trends suggest a rise in the contributions of human pharmaceuticals into coastal ecosystems, underpinning an increasing demand to evaluate the ecotoxicological effects and implications of drug residues in marine risk assessments. Propranolol, a non-selective β-adrenoceptor blocker, is used worldwide to treat high blood pressure conditions and other related cardiovascular conditions. Although diatoms lack β-adrenoceptors, this microalgal group presents receptor-like kinases and proteins with a functional analogy to the animal receptors and that can be targeted by propranolol. In the present work, the authors evaluated the effect of this non-selective β-adrenoceptor blocker in diatom cells using P. tricornutum as a model organism, to evaluate the potential effect of this compound in cell physiology (growth, lipids and energy metabolism and oxidative stress) and its potential relevance for marine ecosystems. Propranolol exposure leads to a significant reduction in diatom cell growth, more evident in the highest concentrations tested. This is likely due to the observed impairment of the main primary photochemistry processes and the enhancement of the mitochondrial respiratory activity. More specifically, propranolol decreased the energy transduction from photosystem II (PSII) to the electron transport chain, leading to an increase in oxidative stress levels. Cells exposed to propranolol also exhibited high-dissipated energy flux, indicating that this excessive energy is efficiently diverted, to some extent, from the photosystems, acting to prevent irreversible photoinhibition. As energy production is impaired at the PSII donor side, preventing energy production through the electron transport chain, diatoms appear to be consuming storage lipids as an energy backup system, to maintain essential cellular functions. This consumption will be attained by an increase in respiratory activity. Considering the primary oxygen production and consumption pathways, propranolol showed a significant reduction of the autotrophic O₂ production and an increase in the heterotrophic mitochondrial respiration. Both mechanisms can have negative effects on marine trophic webs, due to a decrease in the energetic input from marine primary producers and a simultaneous oxygen production decrease for heterotrophic species. In ecotoxicological terms, bio-optical and fatty acid data appear as highly efficient tools for ecotoxicity assessment, with an overall high degree of classification when these traits are used to build a toxicological profile, instead of individually assessed.

Gene co-expression analysis reveals transcriptome divergence between wild and cultivated chickpea under drought stress

Ancestral adaptations in crop wild relatives can provide a genetic reservoir for crop improvement. Here we document physiological changes to mild and severe drought stress, and the associated transcriptome dynamics in both wild and cultivated chickpea. Over 60% of transcriptional changes were related to metabolism, indicating that metabolic plasticity is a core and conserved drought response. In addition, changes in RNA processing and protein turnover were predominant in the data, suggestive of broad restructuring of the chickpea proteome in response to drought. While 12% of the drought-responsive transcripts have similar dynamics in cultivated and wild accessions, numerous transcripts had expression patterns unique to particular genotypes, or that distinguished wild from cultivated genotypes and whose divergence may be a consequence of domestication. These and other comparisons provide a transcriptional correlate of previously described species' genetic diversity, with wild accessions well differentiated from each other and from cultivars, and cultivars essentially indistinguishable at the broad transcriptome level. We identified metabolic pathways such as phenylpropanoid metabolism, and biological processes such as stomatal development, which are differentially regulated across genotypes with potential consequences on drought tolerance. These data indicate that wild Cicer reticulatum may provide both conserved and divergent mechanisms as a resource in breeding for drought tolerance in cultivated chickpea.

CRISPR/Cas9 edited HSFA6a and HSFA6b of Arabidopsis thaliana offers ABA and osmotic stress insensitivity by modulation of ROS homeostasis

The role of Heat Shock Transcription Factor 6 (HSFA6a & HSFA6b) in response to abiotic stresses such as ABA, drought, salinity, drought, and osmotic stress is individually well established. Unfortunately, the functional redundancy between the HSFA6a and HSFA6b as well as the consequences of simultaneous editing of both in response to aforementioned stresses remains elusive. Therefore, this study was designed with the aim of addressing whether there is any functional redundancy between HSFA6a and HSFA6b as well as to decipher their role in abiotic stresses tolerance in Arabidopsis thaliana, by using the CRISPR-Cas9. We have generated the single (hsfa6a and hsfa6b) as well as double mutants (hsfa6a/hsfa6b-1 and hsfa6a/hsfa6b-2) of HSFA6a and HSFA6b with higher frequencies of deletion, insertion, and substitution. The phenotypic characterization of generated double and single mutants under abiotic stresses such as ABA, mannitol, and NaCl identified double mutants more tolerant to subjected abiotic stresses than those of their single mutants. It warrants mentioning that we have identified that HSFA6a and HSFA6b also involved in other major ABA responses, including ABA-inhibited seed germination, stomatal movement, and water loss. In addition to the above, the simultaneous editing of HSFA6a and HSFA6b lead to a reduced ROS accumulation, accompanied by increased expression of much abiotic stress and ABA-responsive genes, including involved in regulation of ROS level. In conclusion, these results suggest that HSFA6a and HSFA6b may offer abiotic stress tolerance by regulating the ROS homeostasis in plants.

Effect of Heavy Metal Contamination in the Environment on Antioxidant Function in Wumeng Semi-fine Wool Sheep in Southwest China

Many environmental accidents have led to worldwide heavy metal pollution, raising concern about heavy metal toxicity in Southwest China. To study the effects of Cd and Pb in the environment on antioxidant function in Wumeng semi-fine wool sheep, contents of Cu, Zn, Mn, Mo, Fe, Se, Cd, and Pb were measured in irrigation water, soil, herbage, and animal tissues. Hematological and biochemical parameters were also determined. The concentrations of Cu, Zn, Cd, and Pb in affected samples of irrigation water, soil, herbage, and tissues were significantly higher than those in the control (P < 0.01). There was no significant difference in other element contents between affected pastures and control areas. The occurrence of anemia affected Wumeng semi-fine wool sheep. The activities of SOD, CAT, and GSH-Px in affected animals were significantly decreased than those in the control (P < 0.01). Content of MDA in serum in affected animals was significantly increased than that in control (P < 0.01). Serum T-AOC in affected animal was significantly lower than that in control (P < 0.01). Consequently, it is suggested that heavy metal contamination in natural habitat caused serious harm to antioxidant function in Wumeng semi-fine wool sheep.

Physiological responses to water deficiency in bread wheat (Triticum aestivum L.) lines with genetically different leaf pubescence

Studying the relationship between leaf pubescence and drought resistance is important for assessing Triticum aestivum L. genetic resources. The aim of the work was to assess resistance of common wheat genotypes with different composition and allelic state of genes that determine the leaf pubescence phenotype. We compared the drought resistance wheat variety Saratovskaya 29 (S29) with densely pubescent leaves, carrying the dominant alleles of the Hl1 and Hl3 genes, and two near isogenic lines, i: S29 hl1, hl3 and i: S29 Hl2aesp, with the introgression of the additional pubescence gene from diploid species Aegilops speltoides. Under controlled conditions of the climatic chamber, the photosynthetic pigments content, the activity of ascorbate-glutathione cycle enzymes and also the parameters of chlorophyll fluorescence used to assess the physiological state of the plants photosynthetic apparatus were studied in the leaves of S29 and the lines. Tolerance was evaluated using the comprehensive index D, calculated on the basis of the studied physiological characteristics. The recessive state of pubescence genes, as well as the introduction of the additional Hl2aesp gene, led to a 6-fold decrease in D. Under the water deficit influence, the fluorescence parameters profile changed in the lines, and the viability index decreased compared with S29. Under drought, the activity of ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase in the line i: S29 hl1, hl3 decreased 1.9, 3.3 and 2.3 times, in the line i: S29 Hl2aesp it decreased 1.8, 3.6 and 1.8 times respectively, compared with S29. In a hydroponic greenhouse, line productivity was studied. Compared with S29, the thousand grains mass in the line i: S29 hl1, hl3 under water deficit was reduced. The productivity of the line i: S29 Hl2aesp was significantly reduced regardless of water supply conditions in comparison with S29. Presumably, the revealed effects are associated with violations of cross-regulatory interactions between the proteins of the trichome formation network and transcription factors that regulate plant growth and stress response.

Comparative Genomic and Physiological Analyses of a Superoxide Dismutase Mimetic (SODm-123) for Its Ability to Respond to Oxidative Stress in Tomato Plants

Superoxide dismutases (SODs) are a group of enzymes that have a crucial role in controlling oxidative stress in plants. Here, we synthesized an environmentally friendly SOD mimic, SODm-123, from L-aspartic acid and manganese oxide. SODm-123 showed similar enzymatic activity to Mn-SOD. To gain insights into the role of SODm-123 in oxidative stress tolerance, a series of experiments were conducted to assess the physiological and molecular responses of tomato plants when treated with SODm-123. The results showed that the levels of O₂^-• and H₂O₂ in tomato cells were affected by SODm-123 treatment, indicating that SODm-123 can control oxidative stress like Mn-SOD. The results also exhibited that SODm-123 increased the contents of photosynthetic pigments. However, it was noted that SODm-123 resulted in a reduction in the content of soluble sugar and MDA. These results indicate that SODm-123 promoted the efficiency of photosynthesis by regulating the content of H₂O₂. To further investigate the role of SODm-123 in controlling oxidative stress, a transcriptome analysis was used to identify differentially expressed genes (DEGs) associated with SODm-123 treatment. The results indicated that SODm-123 treatment resulted in 341 differentially expressed genes (DEGs) in treated tomato leaves at 96 h after treatment. Kyoto encyclopedia of genes and genomes (KEGG) revealed that DEGs were involved in pathways such as photosynthetic pigment biosynthesis, ABC transporters, sugar metabolism, and MAPK signaling, which further confirmed a positive role of SODm-123 in improving stress tolerance in plants. Overall, the results of this study suggest that SODm-123 promotes the growth and development of tomato seedlings and therefore can be used as a potential growth-promoting agent for plants.

Synergetic suppression effects upon the combination of UV-C irradiation and berberine on Microcystis aeruginosa and Scenedesmus obliquus in reclaimed water: Effectiveness and mechanisms

The risk of harmful algal blooms (HABs) in the water recharged with reclaimed water is a bottleneck for water reuse. The suppression effects and mechanisms of the combination of UV-C and berberine on Microcystis aeruginosa and Scenedesmus obliquus in reclaimed water were investigated. Mono UV-C irradiation at 75 mJ cm^-2 could suppress the growth of M. aeruginosa for 7 d and that at 90 mJ cm^-2 could suppress the growth of S. obliquus for 5 d. UV-C irradiation combined with 0.2-2 mg L^-1 berberine lengthened the inhibition period of M. aeruginosa to 10- > 22 d and that of S. obliquus to 7- > 22 d and induced more rapid lethal effects on the harmful microalgal cells, in significant synergetic patterns. The combination of UV-C and berberine suppressed total, intracellular and extracellular microcystin-LR (MC-LR) more effectively and decreased the MC-LR quota significantly, which further reduced the risks of microcystin production and release. Furthermore, synergetic mechanisms of the combined treatments were systematically investigated from the aspects of photosynthetic system (photosynthetic activity and pigments), metabolic activity (ATP and membrane potential), oxidation stress (reactive oxygen species (ROS) and glutathione (GSH)), and apoptosis-like cell death (phosphatidylserine (PS) ectropion, caspase-3 activity and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive rate). The combination treatment provided a joint attack of UV-C and berberine on photosynthetic transport chain of photosynthetic system II (PS II), and a synergetic pathway to achieve more severe disruptions in energy metabolism as well as aggravated oxidative stress. The accumulated ROS enhanced increases in programmed cell death (PCD) indicators of both microalgal species, which contributed to the enhancement effects on growth suppression. The results showed that the combination treatment achieved lower dose requirements of both UV-C irradiation and berberine for inducing the same inhibition effects on microalgal cells, which was promising to be applied in the HABs control of reclaimed water.

Valorization of Moroccan Crocus sativus L. By-products: Foliar Spraying of Aqueous Tepal Extract Stimulates Growth and Confers Antioxidant Properties in Eggplant Seedling under Greenhouse Conditions

The valorization of Crocus sativus L. by-products has become important given its interesting content of bioactive molecules. In the present study, aqueous tepal extract (ATE) studied eggplant seedling's growth and physiology under a plastic tunnel. ATE was foliage sprayed 3 times every 15 days, with various concentrations (1 mg/mL, 2 mg/mL, 3 mg/mL) in addition to a treatment containing 2 mg/mL of tepals and 0.6 mg/mL of stigmas (T+S). The concentration of 2 mg/L ATE significantly (p ≤ 0.05) increased the plant's height, the chlorophyll content, and decreased antioxidant activity and MDA (malondialdehyde). However, the concentration 3 mg/mL inhibited the plant growth; increased the content of ascorbic acid and polyphenol; and resulted in lipid peroxidation and antioxidant activities increases, indicating oxidative stress (p ≤ 0.05). On the other hand, T+S significantly influenced some parameters analyzed. Our findings demonstrate that ATE can act as a biostimulant at 2 mg/mL to enhance eggplant growth in plastic tunnel production and used in plant stress situations.

Unraveling the impact of arsenic on the redox response of peanut plants inoculated with two different Bradyrhizobium sp. strains

Arsenic (As) can be present naturally in groundwater from peanut fields, constituting a serious problem, as roots can accumulate and mobilize the metalloid to their edible parts. Understanding the redox changes in the legume exposed to As may help to detect potential risks to human health and recognize tolerance mechanisms. Thirty-days old peanut plants inoculated with Bradyrhizobium sp. strains (SEMIA6144 or C-145) were exposed to a realistic arsenate concentration, in order to unravel the redox response and characterize the oxidative stress indexes. Thus, root anatomy, reactive oxygen species detection by fluorescence microscopy and, ROS histochemical staining along with the NADPH oxidase activity were analyzed. Besides, photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress indicators. Results showed that at 3 μM As^V, the cross-section areas of peanut roots were augmented; NADPH oxidase activity was significantly increased and O₂˙¯and H₂O₂ accumulated in leaves and roots. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant regardless the inoculated strain, while chlorophylls and carotenes were increased only in those inoculated with Bradyrhizobium sp. C-145. Interestingly, the oxidative burst, mainly induced by the NADPH oxidase activity, and the consequent oxidative stress was strain-dependent and organ-differential. Additionally, As modifies the root anatomy, acting as a possibly first defense mechanism against the metalloid entry. All these findings allowed us to conclude that the redox response of peanut is conditioned by the rhizobial strain, which contributes to the importance of effectively formulating bioinoculants for this crop.

Photosynthetic responses of Arabidopsis to SO2 were related to photosynthetic pigments, photosynthesis gene expression and redox regulation

Sulfur dioxide (SO₂) is one of the most common and harmful air pollutants. High concentrations of SO₂ can induce a series of defensive responses in Arabidopsis plants. However, the role of photosynthesis in the plant response to SO₂ stress is not clear. Here, we report the photosynthetic responses of Arabidopsis plants to SO₂ stress. Exposure to 30 mg/m³ SO₂ decreased stomatal conductance (Gs) and transpiration rate (Tr) but increased photosynthetic pigments and net photosynthetic rate (Pn). The contents of carbohydrates and sucrose were not altered. The transcript levels of most genes related to photosystem II (PSII), cytochrome b6/f (Cytb6f), photosystem I (PSI) and carbon fixation were upregulated, revealing one important regulatory circuit for the maintenance of chloroplast homeostasis under SO₂ stress. Exposure to SO₂ triggered reactive oxygen species (ROS) generation, accompanied by increases in superoxide dismutase (SOD) activity and the contents of cysteine (Cys), glutathione (GSH) and non-protein thiol (NPT), which maintained cellular redox homeostasis. Together, our results indicated that chloroplast photosynthesis was involved in the plant response to SO₂ stress. The photosynthetic responses were related to photosynthetic pigments, photosynthesis gene expression and redox regulation.

Enhancement in the ATP level and antioxidant capacity of Caenorhabditis elegans under continuous exposure to extremely low-frequency electromagnetic field for multiple generations

PURPOSE

Safety concerns about the effects of long-term extremely low-frequency electromagnetic field (ELF-EMF) exposure on human health have been raised. To explore the effects of continuous exposure to ELF-EMF on organisms for multiple generations, we selected Caenorhabditis elegans as a model organism and conducted long-term continuous exposure studies for multiple generations under 20 °C, 50 Hz, and 3 mT ELF-EMF.

MATERIALS AND METHODS

Each generation of worms was treated with ELF-EMF from the egg in the same environment. After long-term exposure to ELF-EMF, the body length of the worms was detected, and 15th generation adult worms were selected as the research object. The ATP level and ATPase were detected, and the expression levels of genes encoding ATP synthase (r53.4, hpo-18, atp-5, unc-32, atp-3) were detected by RT-PCR. In worm's antioxidant system, the level of reactive oxygen species (ROS) was detected by dichlorofluorescein staining, and the total antioxidant capacity (T-AOC), superoxide dismutase (SOD) and catalase (CAT) activity were investigated. The expression of genes encoding superoxide dismutase (sod-1, sod-2, sod-3) was detected in adult (60 h) worms of the fifteenth generation (F15).

RESULTS

These results showed that the body length of F15 worms increased significantly, ATP content increased significantly, ATP synthase activity was significantly enhanced, and the expression levels of the r53.4, hpo-18, atp-5, and atp-3 genes encoding ATPase were significantly upregulated in F15 worms. In addition, SOD activity increased significantly, and the expression levels of the sod-1, sod-2, and sod-3 genes encoding SOD were also significantly upregulated in F15 worms.

CONCLUSIONS

These results indicated that continuous exposure to 50 Hz, 3 mT ELF-EMF for multiple generations can increase the body length of worms, induce the synthesis of ATP and enhance the antioxidant capacity of worms.

A study of light-induced stomatal response in Arabidopsis using thermal imaging

Thermal imaging was used to study the early stage response to light-induced heating of Arabidopsis thaliana leaves. Time-series thermograms provided a spatial and temporal characterization of temperature changes in Arabidopsis wild type and the ost1-2 mutant rosettes exposed to excessive illumination. The initial response to high light, defined by the exponential increase in leaf temperature of ost1-2 gave an increased thermal time constant compared to wild type plants. The inability to regulate stomata in ost1-2 resulted in enhanced stomatal conductance and transpiration rate. Under strong irradiation, a significant decline in the efficiency of photosystem II was observed. This study evaluates infrared thermography kinetics and determines thermal time constants in particular, as an early and rapid method for diagnosing the prime indicators of light stress in plants under excessive light conditions.

The effects of CO2-induced acidification on Tetraselmis biomass production, photophysiology and antioxidant activity: A comparison using batch and continuous culture

A Tetraselmis sp. was selected for its antioxidant activity owing to its high lipid peroxidation inhibition capacity. With the aim to monitor culture conditions to improve antioxidant activity, effects of CO₂-induced acidification on Tetraselmis growth, elemental composition, photosynthetic parameters and antioxidant activity were determined. Two pH values were tested (6.5 and 8.5) in batch and continuous cultures in photobioreactors. Acidification enhanced cell growth under both culture methods. However, the microalgae physiological state was healthier at pH 8.5 than at pH 6.5. Indeed, photosynthetic parameters measured with pulse amplitude modulated (PAM) fluorometry showed a decrease in the photosystem II (PSII) efficiency at pH 6.5 in batch culture. Yet, with the exception of the PSII recovering capacity, photosynthetic parameters were similar in continuous culture at both pH. These results suggest that lowering pH through CO₂-induced acidification may induce a lower conversion of light to chemical energy especially when coupled with N-limitation and/or under un-balanced culture conditions. The highest antioxidant activity was measured in continuous culture at pH 6.5 with an IC₅₀ of 3.44 ± 0.6 μg mL^-1, which is close to the IC₅₀ of reference compounds (trolox and α-tocopherol). In addition, the principal component analysis revealed a strong link between the antioxidant activity and the culture method, the photophysiological state and the nitrogen cell quota and C:N ratio of Tetraselmis sp.. These results highlight Tetraselmis sp. as a species of interest for natural antioxidant production and the potential of PAM fluorometry to monitor culture for production of biomass with a high antioxidant activity.

Reduced phytotoxicity of nonylphenol on tomato (Solanum lycopersicum L.) plants by earthworm casts

Concentrations as high as thousands of milligrams per kilogram (dry weight) of nonylphenol (NP), an endocrine-disrupting chemical of great concern, have been reported in soil. Soil is considered one of the primary pathways for exposure of crop plants to NP. However, there have been few studies on the toxicity of soil NP to crop plants, especially with comprehensive consideration of the application of organic fertiliser which is a common agricultural practice. In this study, tomato plants were grown in soils treated with NP in the presence and/or absence of earthworm casts (EWCs). After four weeks, we tested the physiological and biochemical responses (accumulative levels of hydrogen peroxide (H₂O₂) and superoxide anion radicals (O₂-·), total chlorophyll content, degree of membrane lipid peroxidation, activities of defence-related enzymes, and level of DNA damage) and the changes in plant growth (elongation and biomass). The growth inhibition, reactive oxygen species (H₂O₂ and O₂-·) accumulation, decrease in chlorophyll content, increase in activity of defence-related enzymes (including superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione S-transferase and glutathione reductase), enhancement of membrane lipid peroxidation, and DNA damage in NP-treated seedlings were clearly reversed by the intervention of EWCs. In particular, the suppressed elongation, biomass, and chlorophyll content in tomato plants exposed to NP alone were significantly restored by EWCs to even greater levels than those of the undisturbed control. In other words, EWCs could efficiently invigorate the photosynthesis of crops via up-regulating the chlorophyll content, thereby overwhelming the NP stress on plant growth. Accordingly, except for reducing the bioavailability of soil NP as reported in our previous study, EWCs could also help crop plants to cope with NP stress by strengthening their stress resistance ability. Our findings are of practical significance for the formulation of strategies to relieve the negative effects of soil NP on crop growth.

Hydrogen sulfide promotes rice drought tolerance via reestablishing redox homeostasis and activation of ABA biosynthesis and signaling

Hydrogen sulfide (H₂S) has been explored as the third biologically gasotransmitter regulating plant adaptation response, however, its possible mechanisms on drought tolerance are not completely clear yet. Here, we discovered that during dehydration treatment, the activities of L-cysteine desulfhydrase (LCD), the important synthetic enzymes of H₂S in rice, was enhanced in rice seedling leaves, further leading to continuous increasing of endogenous H₂S production. Pretreatment with NaHS, a well-known H₂S donor, significantly improved rice performance under drought stress. The beneficial roles of NaHS were confirmed by the alleviation of lipid peroxidation, and the activation of antioxidant defence system. Importantly, besides repressing its degradation pathway, NaHS pretreatment promoted ABA de-novo synthesis as well. This resulted in an increase of ABA accumulation and the expression of downstream ABA-responsive genes in rice seedling upon drought stress. Together, the present study illustrated that H₂S improve drought tolerance via reestablishing redox homeostasis and triggering ABA signaling.

Transcriptomic Study for Identification of Major Nitrogen Stress Responsive Genes in Australian Bread Wheat Cultivars

High nitrogen use efficiency (NUE) in bread wheat is pivotal to sustain high productivity. Knowledge about the physiological and transcriptomic changes that regulate NUE, in particular how plants cope with nitrogen (N) stress during flowering and the grain filling period, is crucial in achieving high NUE. Nitrogen response is differentially manifested in different tissues and shows significant genetic variability. A comparative transcriptome study was carried out using RNA-seq analysis to investigate the effect of nitrogen levels on gene expression at 0 days post anthesis (0 DPA) and 10 DPA in second leaf and grain tissues of three Australian wheat (Triticum aestivum) varieties that were known to have varying NUEs. A total of 12,344 differentially expressed genes (DEGs) were identified under nitrogen stress where down-regulated DEGs were predominantly associated with carbohydrate metabolic process, photosynthesis, light-harvesting, and defense response, whereas the up-regulated DEGs were associated with nucleotide metabolism, proteolysis, and transmembrane transport under nitrogen stress. Protein–protein interaction and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis further revealed that highly interacted down-regulated DEGs were involved in light-harvesting and photosynthesis, and up-regulated DEGs were mostly involved in steroid biosynthesis under N stress. The common down-regulated genes across the cultivars included photosystem II 10 kDa polypeptide family proteins, plant protein 1589 of uncharacterized protein function, etc., whereas common up-regulated genes included glutamate carboxypeptidase 2, placenta-specific8 (PLAC8) family protein, and a sulfate transporter. On the other hand, high NUE cultivar Mace responded to nitrogen stress by down-regulation of a stress-related gene annotated as beta-1,3-endoglucanase and pathogenesis-related protein (PR-4, PR-1) and up-regulation of MYB/SANT domain-containing RADIALIS (RAD)-like transcription factors. The medium NUE cultivar Spitfire and low NUE cultivar Volcani demonstrated strong down-regulation of Photosystem II 10 kDa polypeptide family protein and predominant up-regulation of 11S globulin seed storage protein 2 and protein transport protein Sec61 subunit gamma. In grain tissue, most of the DEGs were related to nitrogen metabolism and proteolysis. The DEGs with high abundance in high NUE cultivar can be good candidates to develop nitrogen stress-tolerant variety with improved NUE.