Ascorbic Acid-A Potential Oxidant Scavenger and Its Role in Plant Development and Abiotic Stress Tolerance

Differential Alternative Splicing Genes and Isoform Regulation Networks of Rapeseed (Brassica napus L.) Infected with Sclerotinia sclerotiorum

Alternative splicing (AS) is a post-transcriptional level of gene expression regulation that increases transcriptome and proteome diversity. How the AS landscape of rapeseed (Brassica napus L.) changes in response to the fungal pathogen Sclerotinia sclerotiorum is unknown. Here, we analyzed 18 RNA-seq libraries of mock-inoculated and S. sclerotiorum-inoculated susceptible and tolerant B. napus plants. We found that infection increased AS, with intron retention being the main AS event. To determine the key genes functioning in the AS response, we performed a differential AS (DAS) analysis. We identified 79 DAS genes, including those encoding splicing factors, defense response proteins, crucial transcription factors and enzymes. We generated coexpression networks based on the splicing isoforms, rather than the genes, to explore the genes’ diverse functions. Using this weighted gene coexpression network analysis alongside a gene ontology enrichment analysis, we identified 11 modules putatively involved in the pathogen defense response. Within these regulatory modules, six DAS genes (ascorbate peroxidase 1, ser/arg-rich protein 34a, unknown function 1138, nitrilase 2, v-atpase f, and amino acid transporter 1) were considered to encode key isoforms involved in the defense response. This study provides insight into the post-transcriptional response of B. napus to S. sclerotiorum infection.

Involvement of L-Cysteine Desulfhydrase and Hydrogen Sulfide in Glutathione-Induced Tolerance to Salinity by Accelerating Ascorbate-Glutathione Cycle and Glyoxalase System in Capsicum

The aim of this study is to assess the role of l-cysteine desulfhydrase (l-DES) and endogenous hydrogen sulfide (H₂S) in glutathione (GSH)-induced tolerance to salinity stress (SS) in sweet pepper (Capsicum annuum L.). Two weeks after germination, before initiating SS, half of the pepper seedlings were retained for 12 h in a liquid solution containing H₂S scavenger, hypotaurine (HT), or the l-DES inhibitor dl-propargylglycine (PAG). The seedlings were then exposed for three weeks to control or SS (100 mmol L⁻¹ NaCl) and supplemented with or without GSH or GSH+NaHS (sodium hydrosulfide, H₂S donor). Salinity suppressed dry biomass, leaf water potential, chlorophyll contents, maximum quantum efficiency, ascorbate, and the activities of dehydroascorbate reductase, monodehydroascorbate reductase, and glyoxalase II in plants. Contrarily, it enhanced the accumulation of hydrogen peroxide, malondialdehyde, methylglyoxal, electrolyte leakage, proline, GSH, the activities of glutathione reductase, peroxidase, catalase, superoxide dismutase, ascorbate peroxidase, glyoxalase I, and l-DES, as well as endogenous H₂S content. Salinity enhanced leaf Na⁺ but reduced K⁺; however, the reverse was true with GSH application. Overall, the treatments, GSH and GSH+NaHS, effectively reversed the oxidative stress and upregulated salt tolerance in pepper plants by controlling the activities of the AsA-GSH and glyoxalase-system-related enzymes as well as the levels of osmolytes.

The Apoplast: A Key Player in Plant Survival

The apoplast comprises the intercellular space, the cell walls, and the xylem. Important functions for the plant, such as nutrient and water transport, cellulose synthesis, and the synthesis of molecules involved in plant defense against both biotic and abiotic stresses, take place in it. The most important molecules are ROS, antioxidants, proteins, and hormones. Even though only a small quantity of ROS is localized within the apoplast, apoplastic ROS have an important role in plant development and plant responses to various stress conditions. In the apoplast, like in the intracellular cell compartments, a specific set of antioxidants can be found that can detoxify the different types of ROS produced in it. These scavenging ROS components confer stress tolerance and avoid cellular damage. Moreover, the production and accumulation of proteins and peptides in the apoplast take place in response to various stresses. Hormones are also present in the apoplast where they perform important functions. In addition, the apoplast is also the space where microbe-associated molecular Patterns (MAMPs) are secreted by pathogens. In summary, the diversity of molecules found in the apoplast highlights its importance in the survival of plant cells.

Efficacy of fenugreek plant for ascorbic acid assisted phytoextraction of copper (Cu); A detailed study of Cu induced morpho-physiological and biochemical alterations

Phytoremediation via phyto-extraction is well recognized and sustainable principle for the economical removal of heavy metals from contaminated water and soil. The twofold objective of the present research work was to investigate the remediation potential of fenugreek for Cu under the influence of ascorbic acid (AA). The effect of copper-ascorbic acid chelation on the growth regulation of fenugreek (Trigonella foenum-graceum L.) and its potential to accumulate Cu was investigated in hydroponic medium to optimize concentration with complete randomized design (CRD). Juvenile fenugreek plants were treated with different treatments of AA (5 mM) and Cu (100, 250 and 500 μM). The different morpho-physiological parameters of fenugreek plant such as growth, biomass and chlorophylls were significantly reduced under Cu stress. However, the activities of antioxidant enzymes, electrolyte leakage and reactive oxygen species enhanced with increasing concentration of applied Cu. Results indicated significant increase in plant growth, biomass, physiology and antioxidant enzymes and decrease in reactive oxygen species and electrolyte production in AA mediated fenugreek plants compared to controls and Cu only treated plants. However, it was also found that AA enhanced Cu concentration maximum up to 42% in leaf, 18% in stem and 45% in roots as compared to Cu treated only plants. Moreover, application of AA signified the research results revealing to act as growth regulator and chelator under Cu stress.

Oxidation processes related to seed storage and seedling growth of Malus sylvestris, Prunus avium and Prunus padus

Seeds stored in controlled conditions in gene banks, faster or slower lose their viability. The effects of seed moisture content levels (ca. 5, 8, 11%) combined with storage temperatures (-3°, -18°, -196°C) were investigated in terms of the description of seeds defined as orthodox under oxidative stress after seed storage, during germination, and initial seedling growth. Hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) and ascorbate (Asc) were analyzed in relation to seed germinability and seedlings emergence in three species: Malus sylvestris L., Prunus avium L. and Prunus padus L. The effect of seed storage conditions on H2O2 levels appeared in germinated seeds after the third year of storage in each species. The H2O2 levels were negatively correlated with the germination and seedling emergence of P. avium seeds after three years of storage under all examined combinations. The emergence of P. padus seedlings was not linked to any of the stress markers tested. The P. padus seed biochemical traits were least altered by storage conditions, and the seeds produced tolerant seedlings of relatively high levels of H2O2 and TBARS. To cope with different H2O2 levels, TBARS levels, and Asc levels in seeds of three species varying storage conditions different molecular responses, i.e. repairing mechanisms, were applied during stratification to compensate for the storage conditions and, as a result, seeds remained viable and seedlings were successfully established.

Ecological and Geochemical Conditions for the Accumulation of Antioxidants in the Leaves of Lathyrus maritimus (L.) Bigel

The article explores how location affected the dynamics of accumulation of ascorbic acid (AC) and oxidized forms of AC—dehydroascorbic acid (DAA) and diketogulonic acid (DKGA) in beach pea during ontogenetic development. Our analysis focuses on research of the ecological and geochemical conditions growing of the plant on the Curonian Spit. The level of hydrogen peroxide and the activity of enzymes that break it down were analyzed. Antioxidant activity and the total concentration of phenolics were evaluated in the leaves of beach pea on the leeward and windward sides of the foredune. It was established that the level of AC, DAA, and DKGA was higher in the plants growing on the windward side of the foredune. A higher concentration of peroxy compounds, which stimulate the biosynthesis of antioxidant enzymes (catalase, ascorbate peroxidase), polyphenols, and other low molecular antioxidants (AOA) was observed in the leaves of these plants. The plants on the windward side enter phenological stages one or two weeks later than their counterparts on the leeward side of the foredune do. There was a generally negative correlation between the temperature of the soil and the accumulation of ascorbate system acids in the leaves of the studied plants (r = −0.46/(−0.68), p < 0.05). The accumulation of low molecular antioxidants and enzymes in beach pea suggests their adaptation to the adverse conditions of the windward side of the foredune.

Proteomics, physiological, and biochemical analysis of cross tolerance mechanisms in response to heat and water stresses in soybean

Water stress (WS) and heat stress (HS) have a negative effect on soybean plant growth and crop productivity. Changes in the physiological characteristics, proteome, and specific metabolites investigated on molecular and cellular functions were studied in two soybean cultivars exposed to different heat and water stress conditions independently and in combination. Leaf protein composition was studied using 2-DE and complemented with MALDI TOF mass spectrometry. While the two cultivars displayed genetic variation in response to water and heat stress, thirty-nine proteins were significantly altered in their relative abundance in response to WS, HS and combined WS+HS in both cultivars. A majority of these proteins were involved in metabolism, response to heat and photosynthesis showing significant cross-tolerance mechanisms. This study revealed that MED37C, a probable mediator of RNA polymerase transcription II protein, has potential interacting partners in Arabidopsis and signified the marked impact of this on the PI-471938 cultivar. Elevated activities in antioxidant enzymes indicate that the PI-471938 cultivar can restore the oxidation levels and sustain the plant during the stress. The discovery of this plant's development of cross-stress tolerance could be used as a guide to foster ongoing genetic modifications in stress tolerance.

Exogenous ascorbic acid induces systemic heat stress tolerance in tomato seedlings: transcriptional regulation mechanism

The current study was devoted to assessing the impact of exogenous ascorbic acid (AsA) in inducing systemic thermotolerance against acute heat stress in tomato (Solanum lycopersicum) seedlings. There were four treatment groups including untreated control (CK), heat-stressed tomato (HS: exposure to 40 °C for 8 h), and treated with ascorbic acid (0.5 mM AsA), and the last group includes both the exogenous application of ascorbic acid and heat stress (AsA + HS). The HS led to leaf curling and mild wilting while plants treated with AsA displayed similar phenotype with control plants, approving that AsA eliminated the injurious effects of the heat stress. The oxidative damage to cell components was confirmed by higher levels of hydrogen peroxide, lipid peroxidation, electrolyte leakage, total oxidant status, and oxidative stress index. Moreover, acute heat stress significantly reduced the photosynthetic pigment contents, and nutrient contents in tomato seedling leaves. In contrast, ascorbic acid postulated a priming effect on tomato roots and, substantially, alleviated heat stress effects on seedlings through reducing the oxidative damage and increasing the contents of ascorbic acid, proline, photosynthetic pigments, and upregulation of heat shock proteins in leaves. Ascorbic acid seems to be a key signaling molecule which enhanced the thermotolerance of tomato plants.

A Novel and Potentially MultifacetedDehydroascorbate Reductase Increasing theAntioxidant Systems Is Induced by Beauvericinin Tomato

Dehydroascorbate reductases (DHARs) are important enzymes that reconvert the dehydroascorbic acid (DHA) into ascorbic acid (ASC). They are involved in the plant response to oxidative stress, such as that induced by the mycotoxin beauvericin (BEA). Tomato plants were treated with 50 µM of BEA; the main antioxidant compounds and enzymes were evaluated. DHARs were analyzed in the presence of different electron donors by native and denaturing electrophoresis as well as by western blot and mass spectrometry to identify a novel induced protein with DHAR activity. Kinetic parameters for dehydroascorbate (DHA) and glutathione (GSH) were also determined. The novel DHAR was induced after BEA treatment. It was GSH-dependent and possessed lower affinity to DHA and GSH than the classical DHARs. Interestingly, the mass spectrometry analysis of the main band appearing on sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) revealed a chloroplast sedoheptulose 1,7-bisphosphatase, a key enzyme of the Calvin cycle, and a chloroplast mRNA-binding protein, suggesting that the DHA reducing capacity could be a side activity or the novel DHAR could be part of a protein complex. These results shed new light on the ascorbate-glutathione regulation network under oxidative stress and may represent a new way to increase the plant antioxidant defense system, plant nutraceutical value, and the health benefits of plant consumption.

Organic chelates decrease phytotoxic effects and enhance chromium uptake by regulating chromium-speciation in castor bean (Ricinus communis L.)

There is limited information available on changes in the uptake of essential nutrients and secondary metabolites accumulation in castor bean under Cr toxicity. Besides, the role of organic chelates (EDTA and citric acid) mediated improvement in Cr uptake by castor bean is mostly unknown. Three independent experiments (sand, hydroponics, and soil) were executed to determine the Cr phytoextraction potential of Ricinus communis L. In the sand experiment, optimum doses of organic chelates (EDTA and citric acid) were selected. These optimum doses of chelates were used in the hydroponics and soil experiments. The results of hydroponics and soil experiments manifested a significant decrease in growth characteristics and leaf pigments in response to Cr stress applied as K2Cr2O7 (a source of Cr6+). The application of organic chelates (2.5 and 5 mM) showed a noticeable improvement in oxidative defense and secondary metabolites accumulation that might have decreased oxidative injury reflected as lower hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents. Moreover, chelates improved the uptake of essential nutrients (K+, Ca2+, Mg2+, Fe2+ and P) alongside significant enhancement in total Cr contents of plants. Our results advocated that chelates application resulted in greater endogenous levels of Cr3+ in plants compared with Cr6+ which is more toxic. In nutshell, organic chelates improved growth by regulating Cr species, ion homeostasis and secondary metabolites accumulation in Ricinus communis L.

Methyl Jasmonate Applications From Flowering to Ripe Fruit Stages of Strawberry (Fragaria × ananassa 'Camarosa') Reinforce the Fruit Antioxidant Response at Post-harvest

Preharvest applications of methyl jasmonate (MeJA) have been shown to improve post-harvest fruit quality in strawberry fruit. However, the effectiveness of consecutive field applications at different phenological stages on the reinforcement of the antioxidant capacity remains to be analyzed. To determine the best antioxidant response of strawberry (Fragaria × ananassa 'Camarosa') fruit to different numbers and timing of MeJA applications, we performed three differential preharvest treatments (M1, M2, and M3) consisted of successive field applications of 250 μmol L^-1 MeJA at flowering (M3), large green (M2 and M3), and ripe fruit stages (M1, M2, and M3). Then, we analyzed their effects on fruit quality parameters [firmness, skin color, soluble solids content/titratable acidity (SSC/TA) ratio, fruit weight at harvest, and weight loss] along with anthocyanin and proanthocyanidin (PA) accumulation; the antioxidant-related enzymatic activity of catalase (CAT), guaiacol peroxidase (POX), and ascorbate peroxidase (APX); the total flavonoid and phenolic contents, antioxidant capacity, and ascorbic acid content (AAC) during post-harvest storage (0, 24, 48, and 72 h). We also evaluated the effect on lignin, total carbon and nitrogen (%C and N), lipid peroxidation, and C and N isotopes signatures on fruits. Remarkably, the results indicated that MeJA treatment increases anthocyanin and PA contents as well as CAT activity in post-harvest storage, depending on the number of preharvest MeJA applications. Also, M3 fruit showed a higher AAC compared to control at 48 and 72 h. Noticeably, the anthocyanin content and CAT activity were more elevated in M3 treatment comparing with control at all post-harvest times. In turn, APX activity was found higher on all MeJA-treated fruit independent of the number of applications. Unlike, MeJA applications did not generate variations on fruit firmness and weight, lignin contents,% C and N, and in lipid peroxidation and water/nitrogen use efficiency according to C and N isotope discrimination. Finally, we concluded that an increasing number of MeJA applications (M3 treatment) improve anthocyanin, PA, AAC, and CAT activity that could play an essential role against reactive oxygen species, which cause stress that affects fruits during post-harvest storage.

Enhanced Vitamin C Production Mediated by an ABA-Induced PTP-like Nucleotidase Improves Plant Drought Tolerance in Arabidopsis and Maize

Abscisic acid (ABA) is a key phytohormone that mediates environmental stress responses. Vitamin C, or L-ascorbic acid (AsA), is the most abundant antioxidant protecting against stress damage in plants. How the ABA and AsA signaling pathways interact in stress responses remains elusive. In this study, we characterized the role of a previously unidentified gene, PTPN (PTP-like Nucleotidase) in plant drought tolerance. In Arabidopsis, (AtPTPN was expressed in multiple tissues and upregulated by ABA and drought treatments. Loss-of-function mutants of AtPTPN were hyposensitive to ABA but hypersensitive to drought stresses, whereas plants with enhanced expression of AtPTPN showed opposite phenotypes to . Overexpression of maize PTPN (ZmPTPN) promoted, while knockdown of ZmPTPN inhibited plant drought tolerance, indicating conserved and positive roles of PTPN in plant drought tolerance. We found that both AtPTPN and ZmPTPN release Pi by hydrolyzing GDP/GMP/dGMP/IMP/dIMP, and that AtPTPN positively regulated AsA production via endogenous Pi content control. Consistently, overexpression of VTC2, the rate-limiting synthetic enzyme in AsA biosynthesis, promoted AsA production and plant drought tolerance, and these effects were largely dependent on AtPTPN activity. Furthermore, we demonstrated that the heat shock transcription factor HSFA6a directly binds the AtPTPN promoter and activates AtPTPN expression. Genetic analyses showed that AtPTPN is required for HSFA6a to regulate ABA and drought responses. Taken together, our data indicate that PTPN-mediated crosstalk between the ABA signaling and AsA biosynthesis pathways positively controls plant drought tolerance.

Physiological and biochemical responses of Amaranthus cruentus to polycyclic aromatic hydrocarbon pollution caused by thermal power units

Pollution due to release of polycyclic aromatic hydrocarbons from thermal power plants is a major global issue as the same is highly toxic and carcinogenic. The current research aims to investigate the responses of a dietary plant Amaranthus cruentus towards PAH pollution. For the said purpose, the plant was collected from agricultural land in close vicinity to thermal power units and the effects of PAH pollution on its chlorophyll and various nutraceutical content was evaluated. Oxidative stress biomarkers and antioxidant defense enzymes status and PAH accumulation was quantified as well. Real-time evidence of cell death, depletion of nutraceutical resources, and stomata configuration was generated through various histochemical studies and SEM analysis. Results indicated significant decline of chlorophyll a to the extent of 77% when compared to control. Oxidative stress markers, namely, superoxide radical, H₂O₂, and hydroxyl radical in pollution exposed plants were 12.7, 2.2, and 2.4 times respectively higher over the control which eventually resulted in 35% more cell death for the pollution exposed group. Total phenolics and flavonoids showed a decline of 57.6% and 41.3% respectively in the group exposed to PAH pollution. Similar decreasing trend was also observed for ascorbic acid, α-tocopherol, β-carotene, total proteins, and carbohydrate contents as well. PAH-induced stress also resulted in complete imbalance in the redox homeostasis of the plant which was evident from increase in super oxide dismutase, catalase, and peroxidase antioxidant enzymes by more than 2-fold when compared to control. PAH accumulation in sample group was 10-20 times more when compared to control. Proteomic analysis also indicated upregulation of some proteins related to stress situation. Results are evident of the fact that severe depletion of nutraceutical resources of dietary plants can take place if subjected to oxidative stress arising from PAH pollution.

Targeted delivery of nanomaterials with chemical cargoes in plants enabled by a biorecognition motif

Current approaches for nanomaterial delivery in plants are unable to target specific subcellular compartments with high precision, limiting our ability to engineer plant function. We demonstrate a nanoscale platform that targets and delivers nanomaterials with biochemicals to plant photosynthetic organelles (chloroplasts) using a guiding peptide recognition motif. Quantum dot (QD) fluorescence emission in a low background window allows confocal microscopy imaging and quantitative detection by elemental analysis in plant cells and organelles. QD functionalization with β-cyclodextrin molecular baskets enables loading and delivery of diverse chemicals, and nanoparticle coating with a rationally designed and conserved guiding peptide targets their delivery to chloroplasts. Peptide biorecognition provides high delivery efficiency and specificity of QD with chemical cargoes to chloroplasts in plant cells in vivo (74.6 ± 10.8%) and more specific tunable changes of chloroplast redox function than chemicals alone. Targeted delivery of nanomaterials with chemical cargoes guided by biorecognition motifs has a broad range of nanotechnology applications in plant biology and bioengineering, nanoparticle-plant interactions, and nano-enabled agriculture.

Insights into nitric oxide-mediated water balance, antioxidant defence and mineral homeostasis in rice (Oryza sativa L.) under chilling stress

Being a chilling-sensitive staple crop, rice (Oryza sativa L.) is vulnerable to climate change. The competence of rice to withstand chilling stress should, therefore, be enhanced through technological tools. The present study employed chemical intervention like application of sodium nitroprusside (SNP) as nitric oxide (NO) donor and elucidated the underlying morpho-physiological and biochemical mechanisms of NO-mediated chilling tolerance in rice plants. At germination stage, germination indicators were interrupted by chilling stress (5.0 ± 1.0 °C for 8 h day^-1), while pretreatment with 100 μM SNP markedly improved all the indicators. At seedling stage (14-day-old), chilling stress caused stunted growth with visible toxicity along with alteration of biochemical markers, for example, increase in oxidative stress markers (superoxide, hydrogen peroxide, and malondialdehyde) and osmolytes (total soluble sugar; proline and soluble protein content, SPC), and decrease in chlorophyll (Chl), relative water content (RWC), and antioxidants. However, NO application attenuated toxicity symptoms with improving growth attributes which might be related to enhance activities of antioxidants, mineral contents, Chl, RWC and SPC. Furthermore, principal component analysis indicated that water imbalance and increased oxidative damage were the main contributors to chilling injury, whereas NO-mediated mineral homeostasis and antioxidant defense were the critical determinants for chilling tolerance in rice. Collectively, our findings revealed that NO protects against chilling stress through valorizing cellular defense mechanisms, suggesting that exogenous application of NO could be a potential tool to evolve cold tolerance as well as climate resilience in rice.

Role of Ascorbic acid, Glutathione and Proline Applied as Singly or in Sequence Combination in Improving Chickpea Plant through Physiological Change and Antioxidant Defense under Different Levels of Irrigation Intervals

In recent years, the harmful effects of drought stress have been be mitigated by using bioactive compounds such as antioxidants and osmolytes. In this research, pot experiments were carried out to investigate the effects of ascorbic acid, glutathione and proline on alleviating the harmful effect of drought stress in chickpea plants during season 2017. Chickpea plant seeds were soaked in ascorbic acid (0.75 mM), glutathione (0.75 mM), proline (0.75 mM) singly and/or in sequence combinations for 4 h and then planted in pots. The pots were irrigated with water after seven days (to serve as control), after 14 days (moderate drought stress) and after 28 days (severe drought stress). The sequence combination of antioxidants and proline under drought stress has not been studied yet. The results showed significantly decreased in plant growth, yielding characteristics, photosynthetic pigments and soluble protein content in response to moderate and severe drought stress. Moreover, treatment with antioxidants caused increment the antioxidant enzyme activity, non-enzymatic antioxidant (ascorbic acid and glutathione) contents and endogenous proline in stressed and unstressed plants. In conclusion, The sequence combination of antioxidants and proline caused improvement in plant growth under drought stress by up-regulating the antioxidant defense system and osmolyte synthesis.

Exogenous Ascorbic Acid Induced Chilling Tolerance in Tomato Plants Through Modulating Metabolism, Osmolytes, Antioxidants, and Transcriptional Regulation of Catalase and Heat Shock Proteins

Chilling, a sort of cold stress, is a typical abiotic ecological stress that impacts the development as well as the growth of crops. The present study was carried to investigate the role of ascorbic acid root priming in enhancing tolerance of tomato seedlings against acute chilling stress. The treatments included untreated control, ascorbic acid-treated plants (AsA; 0.5 mM), acute chilling-stressed plants (4 °C), and chilling stressed seedlings treated by ascorbic acid. Exposure to acute chilling stress reduced growth in terms of length, fresh and dry biomass, pigment synthesis, and photosynthesis. AsA was effective in mitigating the injurious effects of chilling stress to significant levels when supplied at 0.5 mM concentrations. AsA priming reduced the chilling mediated oxidative damage by lowering the electrolyte leakage, lipid peroxidation, and hydrogen peroxide. Moreover, up regulating the activity of enzymatic components of the antioxidant system. Further, 0.5 mM AsA proved beneficial in enhancing ions uptake in normal and chilling stressed seedlings. At the gene expression level, AsA significantly lowered the expression level of CAT and heat shock protein genes. Therefore, we theorize that the implementation of exogenous AsA treatment reduced the negative effects of severe chilling stress on tomato.

Over-expression of chickpea glutaredoxin (CaGrx) provides tolerance to heavy metals by reducing metal accumulation and improved physiological and antioxidant defence system

Glutaredoxins (Grxs) are small multifunctional redox proteins. Grxs have glutathione-dependent oxidoreductase activity in the presence of glutathione reductase and NADPH. The role of Grxs is well studied in heavy metal tolerance in prokaryotic and mammalian systems but not in plant genera. In the present study, a chickpea glutaredoxin (CaGrx) gene (LOC101493651) has been investigated against metal stress based on its primary screening in chickpea which revealed higher up-regulation of CaGrx gene under various heavy metals (AsIII-25 μM, AsV-250 μM, Cr(VI)-300 μM, and Cd-500 μM) stress. This CaGrx gene was overexpressed in Arabidopsis thaliana and investigated various biochemical and physiological performances under each metal stress. Transgenic plants showed significant up-regulation of the CaGrx gene during qRT-PCR analysis as well as longer roots, higher seed germination, and survival efficiency during each metal stress. The levels of stress markers, TBARS, H₂O_2, and electrolyte leakage were found to be less in transgenic lines as compared to WT revealed less toxicity in transgenics. The total accumulation of AsIII, AsV, and Cr(VI) were significantly reduced in all transgenic lines except Cd, which was slightly reduced. The physiological parameters such as net photosynthetic rate (P_N), stomatal conductance (g_s), transpiration (E), water use efficiency (WUE), photochemical quenching (qP), and electron transport rate (ETR), were maintained in transgenic lines during metal stress. Various antioxidant enzymes such as glutaredoxin (GRX), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione-S-transferase (GST), ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), antioxidant molecules (ascorbate, GSH) and stress-responsive amino acids (proline and cysteine) levels were significantly increased in transgenic lines which provide metal tolerance. The outcome of this study strongly indicates that the CaGrx gene participates in the moderation of metal stress in Arabidopsis, which can be utilized in biotechnological interventions to overcome heavy metal stress conditions in different crops.

Comparative Proteomic Analysis by iTRAQ Reveals that Plastid Pigment Metabolism Contributes to Leaf Color Changes in Tobacco (Nicotiana tabacum) during Curing

Tobacco (Nicotiana tabacum), is a world's major non-food agricultural crop widely cultivated for its economic value. Among several color change associated biological processes, plastid pigment metabolism is of trivial importance in postharvest plant organs during curing and storage. However, the molecular mechanisms involved in carotenoid and chlorophyll metabolism, as well as color change in tobacco leaves during curing, need further elaboration. Here, proteomic analysis at different curing stages (0 h, 48 h, 72 h) was performed in tobacco cv. Bi'na1 with an aim to investigate the molecular mechanisms of pigment metabolism in tobacco leaves as revealed by the iTRAQ proteomic approach. Our results displayed significant differences in leaf color parameters and ultrastructural fingerprints that indicate an acceleration of chloroplast disintegration and promotion of pigment degradation in tobacco leaves due to curing. In total, 5931 proteins were identified, of which 923 (450 up-regulated, 452 down-regulated, and 21 common) differentially expressed proteins (DEPs) were obtained from tobacco leaves. To elucidate the molecular mechanisms of pigment metabolism and color change, 19 DEPs involved in carotenoid metabolism and 12 DEPs related to chlorophyll metabolism were screened. The results exhibited the complex regulation of DEPs in carotenoid metabolism, a negative regulation in chlorophyll biosynthesis, and a positive regulation in chlorophyll breakdown, which delayed the degradation of xanthophylls and accelerated the breakdown of chlorophylls, promoting the formation of yellow color during curing. Particularly, the up-regulation of the chlorophyllase-1-like isoform X2 was the key protein regulatory mechanism responsible for chlorophyll metabolism and color change. The expression pattern of 8 genes was consistent with the iTRAQ data. These results not only provide new insights into pigment metabolism and color change underlying the postharvest physiological regulatory networks in plants, but also a broader perspective, which prompts us to pay attention to further screen key proteins in tobacco leaves during curing.

Mapping the Salt Stress-Induced Changes in the Root miRNome in Pokkali Rice

A plant's response to stress conditions is governed by intricately coordinated gene expression. The microRNAs (miRs) have emerged as relatively new players in the genetic network, regulating gene expression at the transcriptional and post-transcriptional level. In this study, we performed comprehensive profiling of miRs in roots of the naturally salt-tolerant Pokkali rice variety to understand their role in regulating plant physiology in the presence of salt. For comparisons, root miR profiles of the salt-sensitive rice variety Pusa Basmati were generated. It was seen that the expression levels of 65 miRs were similar for roots of Pokkali grown in the absence of salt (PKNR) and Pusa Basmati grown in the presence of salt (PBSR). The salt-induced dis-regulations in expression profiles of miRs showed controlled changes in the roots of Pokkali (PKSR) as compared to larger variations seen in the roots of Pusa Basmati. Target analysis of salt-deregulated miRs identified key transcription factors, ion-transporters, and signaling molecules that act to maintain cellular Ca2+ homeostasis and limit ROS production. These miR:mRNA nodes were mapped to the Quantitative trait loci (QTLs) to identify the correlated root traits for understanding their significance in plant physiology. The results obtained indicate that the adaptability of Pokkali to excess salt may be due to the genetic regulation of different cellular components by a variety of miRs.

Effects of temperature stress on the accumulation of ascorbic acid and folates in sweet corn (Zea mays L.) seedlings

BACKGROUND

Extreme temperatures are among the primary abiotic stresses that affect plant growth and development. Ascorbic acid (AsA) is an efficient antioxidant for scavenging relative oxygen species accumulated under stress. Folates play a significant role in DNA synthesis and protect plants against oxidative stress. Sweet corn (Zea mays L.), a crop grown worldwide, is sensitive to extreme temperatures at seedling stage, which may cause yield loss. This study was conducted to explore the biosynthetic regulative mechanism of AsA and folates in sweet corn seedlings under temperature stress.

RESULTS

The AsA and folate composition and relative gene expression in sweet corn seedlings grown under different temperature stresses (10, 25, and 40 °C) were evaluated. The imposition of temperature stress altered the AsA content mainly by modulating the expression of _Zm DHAR, whose encoded enzyme dehydroascorbic reductase (DHAR) is essential in the AsA recycle pathway. Low temperature stress raised the expressions of relative genes, leading to folate accumulation. High temperature stress modulated the folate content by influencing the expression of the correspondence gene for aminodeoxychorismate synthase, _Zm ADCS, as well as downstream genes that connected with DNA methylation.

CONCLUSION

These results provided a theoretical basis, at a genetic level, for understanding the stress responses mechanism in sweet corn seedlings, offering guidance for sweet corn cultivation. © 2019 Society of Chemical Industry.

Foliar applied fullerol differentially improves salt tolerance in wheat through ion compartmentalization, osmotic adjustments and regulation of enzymatic antioxidants

Earlier we reported that seed pre-treatment with PHF promoted early seedling growth and salinity tolerance in wheat. As a way forward, experiments were conducted to investigate whether and to what extent foliar spray of fullerol could influence growth and physio-biochemical responses in salt stressed wheat. In a control experiment, seeds were sown in sand filled pots (500 g) under control and 150 mM NaCl stress. After 15 days, foliar spray of fullerol at 0, 10, 40, 80 and 120 nM concentration was applied and the data for various morpho-biochemical attributes recorded after 2 weeks. Fullerol caused improvements in shoot growth attributes while had least effect on root growth traits. Increase in total chlorophyll while reduction in Car/Chl ratio was evident under salinity in response to fullerol spray. Only 40 and 80 nM spray treatments improved antioxidant activities and reduced H2O2 contents while MDA contents which increased due to salt stress, remained unaffected by foliar spray. Fullerol spray also improved sugars, proline and free amino acids under salinity. During second experiment under natural conditions, 60 day old plants grown in sand filled pots (10 kg) under 0 and 150 mM NaCl were foliar sprayed with selected concentrations (0, 40 and 80 nM) of fullerol. Salinity inhibited gas exchange and grain yield attributes while fullerol-sprayed plants exhibited recovery. Fullerol spray resulted in high root and shoot K+ and shoot Ca2+ contents. Also, increase in shoot and root P, while lesser shoot Na+ was recorded due to 80 nM spray under salt stress. Overall, 40 and 80 nM fullerol spray improved photosynthetic activity, osmolytes accumulation and altered tissue ion compartmentalization which contributed to improvement in grain yield attributes under salinity.

Vitamin C in Plants: Novel Concepts, New Perspectives, and Outstanding Issues

Significance: The concept that vitamin C (l-ascorbic acid) is at the heart of the peroxide processing and redox signaling hub in plants is well established, but our knowledge of the precise mechanisms involved remains patchy at best. Recent Advances: Ascorbate participates in the multifaceted signaling pathways initiated by both reactive oxygen species (ROS) and reactive nitrogen species. Crucially, the apoplastic ascorbate/dehydroascorbate (DHA) ratio that is regulated by ascorbate oxidase (AO) sculpts the apoplastic ROS (apoROS) signal that controls polarized cell growth, biotic and abiotic defences, and cell to cell signaling, as well as exerting control over the light-dependent regulation of photosynthesis. Critical Issues: Here we re-evaluate the roles of ascorbate in photosynthesis and other processes, addressing the question of how much we really know about the regulation of ascorbate homeostasis and its functions in plants, or how AO is regulated to modulate apoROS signals. Future Directions: The role of microRNAs in the regulation of AO activity in relation to stress perception and signaling must be resolved. Similarly, the molecular characterization of ascorbate transporters and mechanistic links between photosynthetic and respiratory electron transport and ascorbate synthesis/homeostasis are a prerequisite to understanding ascorbate homeostasis and function. Similarly, there is little in vivo evidence for ascorbate functions as an enzyme cofactor.

Effect of copper-resistant Stenotrophomonas maltophilia on maize (Zea mays) growth, physiological properties, and copper accumulation: potential for phytoremediation into biofortification

In this study, Cu-tolerant PGP bacteria were isolated from the contaminated soils of Tapi (Surat, Gujarat, India). From a set of 118 bacteria isolated from the contaminated soil, the isolate RBTS7 was found to be efficient in tolerating 0.3 g (w/v) Cu. The isolate was identified as Stenotrophomonas maltophilia, based on biochemical and 16S rRNA gene sequencing. Further, the isolate was also found to produce indole acetic acid (140 µg/ml) and siderophore, and solubilize potassium. Inoculation study was carried out in the presence and absence of Cu in the greenhouse. The results revealed that S. maltophilia enhanced plant growth and biomasses compared to control. In addition to plant growth attributes, the isolate also enhanced chlorophyll a and b (434.1 and 496.7%) contents and antioxidant properties such as proline (168.2%), total phenolic compounds (33.5%), and ascorbic acid oxidase (62.3%) compared to control with Cu and without Cu. Inoculation of S. maltophilia + Cu enhanced the uptake of Cu in maize root (77.4%) and stem (112.0%) compared to Cu-stressed control. The results clearly indicated the inoculation of S. maltophilia reduced the toxicity of Cu and in turn enhanced the plant growth and mobilization of Cu to the plant parts.

Spermine ameliorates prolonged fluoride toxicity in soil-grown rice seedlings by activating the antioxidant machinery and glyoxalase system

The current manuscript presents the first report on the ameliorative roles of exogenous spermine (Spm) during prolonged fluoride-induced toxicity and oxidative damages in the susceptible rice cultivar, IR-64. The application of Spm increased the overall growth in the stressed seedlings by significantly restricting fluoride bioaccumulation within the shoots and roots. The Spm-treated stressed seedlings exhibited low chlorosis and induced activity of pyruvate dehydrogenase and nitrate reductase due to reduced accumulation and localization of reactive oxygen species (ROS) in the shoot and root. Spm-supplementation during stress reduced the levels of molecular damages by lowering malondialdehyde, electrolyte leakage and protein carbonylation, and lipoxygenase and protease activity due to effective detoxification of ROS by the antioxidants like proline, glycine-betaine, anthocyanin, flavonoids, phenolics and higher polyamines like Spm and spermidine. Excessive accumulation of the toxic methylglyoxal was reversed due to the activation of the glyoxalase system (comprising of glyoxalase I and II) and the ascorbate-glutathione cycle. Exogenous Spm also triggered the activity of superoxide dismutase, guaiacol peroxidase, glutathione peroxidase and phenylalanine ammonia lyase, which efficiently scavenged ROS in the stressed seedlings. Overall, Spm treatment mitigated the fluoride-induced injuries in IR-64 by reducing fluoride bioaccumulation and elaborately refining the various defence machineries.

Towards a Sustainable Agriculture: Strategies Involving Phytoprotectants against Salt Stress

Salinity is one of the main constraints for agriculture productivity worldwide. This important abiotic stress has worsened in the last 20 years due to the increase in water demands in arid and semi-arid areas. In this context, increasing tolerance of crop plants to salt stress is needed to guarantee future food supply to a growing population. This review compiles knowledge on the use of phytoprotectants of microbial origin (arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria), osmoprotectants, melatonin, phytohormones and antioxidant metabolism-related compounds as alleviators of salt stress in numerous plant species. Phytoprotectants are discussed in detail, including their nature, applicability, and role in the plant in terms of physiological and phenotype effects. As a result, increased crop yield and crop quality can be achieved, which in turn positively impact food security. Herein, efforts from academic and industrial sectors should focus on defining the treatment conditions and plant-phytoprotectant associations providing higher benefits.

A metabolomics study of ascorbic acid-induced in situ freezing tolerance in spinach (Spinacia oleracea L.)

Freeze-thaw stress is one of the major environmental constraints that limit plant growth and reduce productivity and quality. Plants exhibit a variety of cellular dysfunctions following freeze-thaw stress, including accumulation of reactive oxygen species (ROS). This means that enhancement of antioxidant capacity by exogenous application of antioxidants could potentially be one of the strategies for improving freezing tolerance (FT) of plants. Exogenous application of ascorbic acid (AsA), as an antioxidant, has been shown to improve plant tolerance against abiotic stresses but its effect on FT has not been investigated. We evaluated the effect of AsA-feeding on FT of spinach (Spinacia oleracea L.) at whole plant and excised-leaf level, and conducted metabolite profiling of leaves before and after AsA treatment to explore metabolic explanation for change in FT. AsA application did not impede leaf growth, instead slightly promoted it. Temperature-controlled freeze-thaw tests revealed AsA-fed plants were more freezing tolerant as indicated by: (a) less visual damage/mortality; (b) lower ion leakage; and (c) less oxidative injury, lower abundance of free radicals ( O 2 · - and H2O2). Comparative leaf metabolite profiling revealed clear separation of metabolic phenotypes for control versus AsA-fed leaves. Specifically, AsA-fed leaves had greater abundance of antioxidants (AsA, glutathione, alpha- & gamma-tocopherol) and compatible solutes (proline, galactinol, and myo-inositol). AsA-fed leaves also had higher activity of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, and catalase). These changes, together, may improve FT via alleviating freeze-induced oxidative stress as well as protecting membranes from freeze desiccation. Additionally, improved FT by AsA-feeding may potentially include enhanced cell wall/lignin augmentation and bolstered secondary metabolism as indicated by diminished level of phenylalanine and increased abundance of branched amino acids, respectively.

Exogenously Applied Ascorbic Acid-Mediated Changes in Osmoprotection and Oxidative Defense System Enhanced Water Stress Tolerance in Different Cultivars of Safflower (Carthamus tinctorious L.)

The present study was conducted to examine the effect of exogenously applied ascorbic acid (AsA) on osmoprotectants and the oxidative defense system in four cultivars (16171, 16183, 16207 and 16246) of safflower under well-watered and water deficit conditions. Water stress (60% field capacity) significantly decreased the shoot and root fresh and dry weights, shoot and root lengths and chlorophyll contents in all four safflower cultivars, while it increased the leaf free proline, total phenolics, total soluble proteins, hydrogen peroxide content and activities of catalase, superoxide dismutase and peroxidase enzymes. Foliar-applied (100 mg L-1 and 150 mg L-1) ascorbic acid caused a marked improvement in shoot and root fresh and dry weights, plant height, chlorophyll and AsA contents as well as the activity of peroxidase (POD) enzyme particularly under water deficit conditions. It also increased the accumulation of leaf proline, total phenolics, total soluble proteins and glycine betaine (GB) content in all four cultivars. Exogenously applied AsA lowered the contents of MDA and H2O2, and the activities of CAT and SOD enzymes. Overall, exogenously applied AsA had a positive effect on the growth of safflower plants under water deficit conditions which could be related to AsA-induced enhanced osmoprotection and regulation of antioxidant defense system.

A Biostimulant Obtained from the Seaweed Ascophyllum nodosum Protects Arabidopsis thaliana from Severe Oxidative Stress

Abiotic stresses cause oxidative damage in plants. Here, we demonstrate that foliar application of an extract from the seaweed Ascophyllum nodosum, SuperFifty (SF), largely prevents paraquat (PQ)-induced oxidative stress in Arabidopsis thaliana. While PQ-stressed plants develop necrotic lesions, plants pre-treated with SF (i.e., primed plants) were unaffected by PQ. Transcriptome analysis revealed induction of reactive oxygen species (ROS) marker genes, genes involved in ROS-induced programmed cell death, and autophagy-related genes after PQ treatment. These changes did not occur in PQ-stressed plants primed with SF. In contrast, upregulation of several carbohydrate metabolism genes, growth, and hormone signaling as well as antioxidant-related genes were specific to SF-primed plants. Metabolomic analyses revealed accumulation of the stress-protective metabolite maltose and the tricarboxylic acid cycle intermediates fumarate and malate in SF-primed plants. Lipidome analysis indicated that those lipids associated with oxidative stress-induced cell death and chloroplast degradation, such as triacylglycerols (TAGs), declined upon SF priming. Our study demonstrated that SF confers tolerance to PQ-induced oxidative stress in A. thaliana, an effect achieved by modulating a range of processes at the transcriptomic, metabolic, and lipid levels.

Plant growth-regulating molecules as thermoprotectants: functional relevance and prospects for improving heat tolerance in food crops

Among various abiotic stresses, heat stress is one of the most damaging, threatening plant productivity and survival all over the world. Warmer temperatures due to climatic anomalies above optimum growing temperatures have detrimental impacts on crop yield potential as well as plant distribution patterns. Heat stress affects overall plant metabolism in terms of physiology, biochemistry, and gene expression. Membrane damage, protein degradation, enzyme inactivation, and the accumulation of reactive oxygen species are some of the harmful effects of heat stress that cause injury to various cellular compartments. Although plants are equipped with various defense strategies to counteract these adversities, their defensive means are not sufficient to defend against the ever-rising temperatures. Hence, substantial yield losses have been observed in all crop species under heat stress. Here, we describe the involvement of various plant growth-regulators (PGRs) (hormones, polyamines, osmoprotectants, antioxidants, and other signaling molecules) in thermotolerance, through diverse cellular mechanisms that protect cells under heat stress. Several studies involving the exogenous application of PGRs to heat-stressed plants have demonstrated their role in imparting tolerance, suggesting the strong potential of these molecules in improving the performance of food crops grown under high temperature.

Stripe rust induced defence mechanisms in the leaves of contrasting barley genotypes (Hordeum vulgare L.) at the seedling stage

Puccinia striiformis f. sp. hordei, the causal organism of stripe rust in barley poses serious threats to its production. The present study examined the seedling response and changes in antioxidant defence system along with NADPH oxidase, hydrogen peroxide, and lipid peroxidation marker-malondialdehyde (MDA) in the four barley genotypes namely Jyoti, RD2900, RD2901, and RD2552 in response to M and G-races of stripe rust pathogen. Disease reaction showed Jyoti as susceptible genotype, RD2901 and RD2552 as resistant, whereas RD2900 behaved differentially to both the races. M-race which is predominant was found to be more virulent than G-race of barley stripe rust pathogen. RD2901 showed an increase in activities of NADPH oxidase, catalase, peroxidase, and enzymes of ascorbate-glutathione pathway along with ascorbate and glutathione pool on inoculation with M-race, which was accompanied by the decrease in hydrogen peroxide and MDA contents. Jyoti, on the other hand, showed an increase in peroxidase and glutathione-S-transferase activities only which were unable to maintain redox homeostasis. The scrutiny of data indicated an increase in ASA/DHA ratio on infection in all the genotypes irrespective of their behaviour towards the races. However, GSH/GSSG ratio significantly declined in Jyoti and increased or remained unaffected in the resistant genotypes which suggested that GSH/GSSG might be playing a vital role in imparting tolerance against stripe rust. Further, correlation studies also revealed that leaf damage was positively correlated with H₂O₂ and MDA contents.

Cu-based metal–organic framework HKUST-1 as effective catalyst for highly sensitive determination of ascorbic acid

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature. Its morphology, structure and composition were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, nitrogen adsorption and desorption isotherms, energy dispersive X-ray spectroscopy (EDS) and elemental analysis (EA). This material was then loaded onto the surface of an indium tin oxide (ITO) electrode to catalyse the electrochemical oxidation of ascorbic acid (AA). An equal-electron-equal-proton reaction was deduced from the pH investigation, and a diffusion-controlled process was reinforced by the dynamics study. Under optimal conditions, the oxidation peak current at +0.02 V displayed a linear relationship with the concentration of AA within the ranges of 0.01–25 and 25–265 mM, respectively. The limit of detection (LOD) was 3 μM at S/N of 3. The superb response could be ascribed to the porous nanosheet structure of HKUST-1, which enhanced both the effective surface area and the electron transfer ability significantly. Moreover, the novel AA sensor demonstrated good reproducibility, favourable stability and high sensitivity towards glucose, uric acid (UA), dopamine (DA) and several amino acids. It was also successfully applied to the real sample testing of various AA-containing tablets.

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature and it demonstrated high capability and sensitivity towards the oxidation of ascorbic acid (AA).

Ascorbate-Mediated Modulation of Cadmium Stress Responses: Reactive Oxygen Species and Redox Status in Brassica napus

The role of ascorbate (AsA) in antioxidant defense system-associated resistance to cadmium (Cd) in oilseed rape plants has not yet been clearly demonstrated. The present study investigated the critical role of exogenous AsA on the physiological and biochemical responses of reactive oxygen species (ROS) and antioxidant scavenging defense systems in oilseed rape (Brassica napus L. cv. Tammi) seedlings exposed to Cd. Cd (10 μM) treatment led to significant reductions in plant growth; increases in the levels of superoxide anion radical, hydrogen peroxide, and malondialdehyde; and increases in Cd uptake and accumulation by the roots and shoots in hydroponically grown 10-day-old seedlings. Moreover, it reduced AsA content and AsA redox ratios, which have been correlated with reductions in glutathione (GSH) and/or nicotinamide adenine dinucleotide phosphate (NADPH) redox status. However, exogenously applying AsA to Cd-exposed seedlings decreased Cd-induced ROS, improved antioxidant defense systems by increasing AsA, GSH, and NADPH contents, and increased Cd uptake and accumulation in both roots and shoots of the plants. These results provided evidence that the enhancement in AsA redox status can be linked to an increase in the GSH and/or NADPH redox ratios through the induction of the AsA-GSH-NADPH cycle. Thus, these results suggest that exogenous AsA application to oilseed rape seedlings under Cd stress might alleviate the overall Cd toxicity by regulating the homeostasis of the AsA-GSH-NADPH cycle, which reestablishes the steady-state cellular redox status.

Vegetable Additives in Food Packaging Polymeric Materials

Plants are the most abundant bioresources, providing valuable materials that can be used as additives in polymeric materials, such as lignocellulosic fibers, nano-cellulose, or lignin, as well as plant extracts containing bioactive phenolic and flavonoid compounds used in the healthcare, pharmaceutical, cosmetic, and nutraceutical industries. The incorporation of additives into polymeric materials improves their properties to make them suitable for multiple applications. Efforts are made to incorporate into the raw polymers various natural biobased and biodegradable additives with a low environmental fingerprint, such as by-products, biomass, plant extracts, etc. In this review we will illustrate in the first part recent examples of lignocellulosic materials, lignin, and nano-cellulose as reinforcements or fillers in various polymer matrices and in the second part various applications of plant extracts as active ingredients in food packaging materials based on polysaccharide matrices (chitosan/starch/alginate).

Ascorbic Acid-The Little-Known Antioxidant in Woody Plants

Reactive oxygen species (ROS) are constantly produced by metabolically active plant cells. The concentration of ROS may determine their role, e.g., they may participate in signal transduction or cause oxidative damage to various cellular components. To ensure cellular homeostasis and minimize the negative effects of excess ROS, plant cells have evolved a complex antioxidant system, which includes ascorbic acid (AsA). AsA is a multifunctional metabolite with strong reducing properties that allows the neutralization of ROS and the reduction of molecules oxidized by ROS in cooperation with glutathione in the Foyer-Halliwell-Asada cycle. Antioxidant enzymes involved in AsA oxidation and reduction switches evolved uniquely in plants. Most experiments concerning the role of AsA have been performed on herbaceous plants. In addition to extending our understanding of this role in additional taxa, fundamental knowledge of the complex life cycle stages of woody plants, including their development and response to environmental factors, will enhance their breeding and amend their protection. Thus, the role of AsA in woody plants compared to that in nonwoody plants is the focus of this paper. The role of AsA in woody plants has been studied for nearly 20 years. Studies have demonstrated that AsA is important for the growth and development of woody plants. Substantial changes in AsA levels, as well as reduction and oxidation switches, have been reported in various physiological processes and transitions described mainly in leaves, fruits, buds, and seeds. Evidently, AsA exhibits a dual role in the photoprotection of the photosynthetic apparatus in woody plants, which are the most important scavengers of ozone. AsA is associated with proper seed production and, thus, woody plant reproduction. Similarly, an important function of AsA is described under drought, salinity, temperature, light stress, and biotic stress. This report emphasizes the involvement of AsA in the ecological advantages, such as nutrition recycling due to leaf senescence, of trees and shrubs compared to nonwoody plants.

Seed Pretreatment and Foliar Application of Proline Regulate Morphological, Physio-Biochemical Processes and Activity of Antioxidant Enzymes in Plants of Two Cultivars of Quinoa (Chenopodium quinoa Willd.)

In the current study, the effects of exogenously applied proline (25 and 50 mM) and low-temperature treatment were examined on the physiochemical parameters in the plants of two cultivars (V1 and V2) of quinoa (Chenopodium quinoa Willd.). The seeds were also exposed to chilling stress at 4 °C before sowing. Plants raised from the seeds treated with low temperature showed reduced plant growth and contents of chlorophyll and carotenoids, but they had significantly increased contents of malondialdehyde, proline, ascorbic acid, total free amino acids, total soluble sugars, and total phenolics, as well as the activity of the peroxidase (POD) enzyme. Cold stress applied to seeds remained almost ineffective in terms of bringing about changes in plant root, hydrogen peroxide, glycine betaine and activities of superoxide dismutase (SOD), and catalase (CAT) enzymes. The exogenous application of proline significantly increased plant growth, the contents of chlorophyll, carotenoids, proline, ascorbic acid, total free amino acids, phenolics, and total soluble sugars, as well as the activities of SOD, POD, and CAT, but it decreased malondialdehyde content. Overall, foliar application of proline was better than the seed treatment in improving root dry weight, root length, chlorophyll a, carotenoids, glycine betaine, ascorbic acid and superoxide dismutase activity, whereas seed pre-treatment with proline was effective in improving shoot dry weight, shoot length, hydrogen peroxide, malondialdehyde, and peroxidase activity in both quinoa cultivars.

Impact of Carbon Nanomaterials on the Antioxidant System of Tomato Seedlings

Tomato is one of the most economically important vegetables worldwide and is constantly threatened by various biotic and abiotic stress factors reducing the quality and quantity in the production of this crop. As an alternative to mitigate stress in plants, carbon nanomaterials (CNMs) have been used in agricultural areas. Therefore, the objective of the present work was to evaluate the antioxidant responses of tomato seedlings to the application via foliar and drench of carbon nanotubes (CNTs) and graphene (GP). Different doses (10, 50, 100, 250, 500, and 1000 mg L-1) and a control were evaluated. The results showed that the fresh and dry root weight increased with the application of CNMs. Regarding the antioxidant responses of tomato seedlings, the application of CNMs increased the content of phenols, flavonoids, ascorbic acid, glutathione, photosynthetic pigments, activity of the enzyme's ascorbate peroxidase, glutathione peroxidase, catalase, and phenylalanine ammonia lyase as well as the content of proteins. Therefore, the use of carbon-based nanomaterials could be a good alternative to induce tolerance to different stress in tomato crop.

Amelioration of Chromium VI Toxicity in Sorghum (Sorghum bicolor L.) using Glycine Betaine

The main objective of the present research work was to study the effect of Cr toxicity and its amelioration by glycine betaine (GB) in sorghum (HJ 541 and SSG 59-3). Chromium (Cr VI), 2 and 4 ppm led to a significant reduction in plant height, root length, chlorophyll content, antioxidant enzymes viz. catalase, peroxidase, ascorbate peroxidase, glutathione reductase, polyphenol oxidase, and superoxide dismutase; and metabolites viz. ascorbate, proline, and glutathione. The results of the present study supported the findings that the application of GB can minimize or reduce the toxic effects caused by Cr VI which reaches the plants via soil, water, and air pollution. It is concluded that GB at both 50, as well as 100 mM concentrations, successfully ameliorated Cr VI (up to 4 ppm) toxicity and its application may be recommended for crops affected by Cr VI toxicity to get better growth and yield.

Phytoextraction of iron from contaminated soils by inoculation of iron-tolerant plant growth-promoting bacteria in Brassica juncea L. Czern

Iron (Fe) is one of the essential micronutrients for all living organisms. Despite its abundance in most of the contaminated soil, it is usually in unavailable forms. The unavailable form of Fe could be mobilized to plants by the use of microorganisms. This study was carried out to show that the Fe-contaminated field soils could be used to accumulate Fe in the plant parts using bacterial inoculation. For this, from a set of bacterial isolates, four Fe-tolerant bacteria were selected and identified based on 16S rRNA gene sequencing. The Fe-tolerant bacteria belonged to the genus Bacillus toyonensis (MG430287), Rhodococcus hoagii (MG432495), Lysinibacillus mangiferihumi (MG432492), and Lysinibacillus fusiformis (MG430290). Screening of plant growth-promoting properties of these isolates revealed that all isolates were able to produce indole acetic acid (50.0-84.0 μg/ml), siderophore, and potassium solubilization (except R. hoagii). Pot assay using Fe-contaminated ((8.07-8.35 g kg^-1) soils River Directorate of India) revealed that Fe-tolerant bacteria enhanced the growth of Brassica juncea and its biomass. Besides the improved plant growth, the inoculated plants also showed an overall percentage increase in the uptake of iron in root, stem, and leaf (57.91-128.31%) compared with uninoculated plants. In addition to enhanced plant growth attributes, the isolates also improved the total chlorophyll content and antioxidant properties such as total phenol, proline, and ascorbic acid oxidase. Thus, the results clearly indicated that these isolates could be used as a bioinoculant to improve the sequestration of Fe from the contaminated soils and alleviation of Fe stress in plants.

Pre-treatment of two contrasting water-stressed genotypes of cassava (Manihot esculenta Crantz) with ascorbic acid. I. Growth, physiological and antioxidant responses

Water deficit-stress at early growth stage is a major constraint of cassava production. Ascorbic acid is a non-enzymatic antioxidant that mitigates oxidative damage caused by water stress in plants. Growth, physiological and antioxidant defense system responses of two contrasting water-stressed cassava genotypes to pre-treatment with foliar application of ascorbic acid (AA) were investigated. The objectives of this study were to assess the growth, proline, photosynthesis pigments and antioxidant activities of young water-stressed cassava plants pre-treated with ascorbic acid. The study consisted of IITA-TMS-IBA980581 (drought tolerant) and IITA-TMS-IBA010040 (drought sensitive) cassava genotypes treated with six doses (0.00, 0.25, 0.50, 0.75 and 1.00 mM) of AA before being subjected to water deficit (45.0% field capacity) and a water sufficient AA-untreated control. In both genotypes, water stress reduced shoot height (40.3%), leaf area (42.5%), and number of root (54.5%), biomass (28.6%), relative water content (RWC, 3.2%) and photosynthetic pigments (300.0%). However, water stress increased proline (91.3%), endogenous AA (112.0%), catalase (CAT, 300.0%) and superoxide dismutase (SOD, 15.3%) in both genotypes. Compared with IITA-TMS-IBA010040, leaf area, biomass, number of root and shoot height of IITA-TMS-IBA980581 were higher by 7.3, 24.6, 25.9 and 13.1%, respectively. By less than a quarter, chlorophylls a and b, activity of superoxide dismutase and relative water content of IITA-TMS-IBA980581 were higher compared with IITA-TMS-IBA010040. However, proline content of IITA-TMS-IBA010040 was higher than IITA-TMS-IBA980581 by 14.3%. Pre-treatment with AA improved growth parameters, photosynthetic pigments, RWC, endogenous AA, activity of CAT and SOD, but decreased proline in both genotypes with an optimum concentration at 0.5 mM. Pre-treatment with 0.5 mM AA increased shoot height, area of leaves, leaf number, number of root and dry weight by 46.3, 44.7, 14.4, 88.2 and 37.5%, respectively. Pre-treatment with 0.5 mM AA doubled chlorophylls, tripled carotenoids content, doubled endogenous AA and slightly enhanced RWC (2.1%) and SOD (2.0%) when compared with AA-untreated water stressed plants. But pre-stress application of AA reduced proline content by one-fold, increased CAT activity by one-fold in IITA-TMS-IBA980581 and by one-third in IITA-TMS-IBA010040. The study concluded that pre-treatment of cassava young plants with AA before water deficit could alleviate oxidative stress.

Targeting Acr3 from Ensifer medicae to the plasma membrane or to the tonoplast of tobacco hairy roots allows arsenic extrusion or improved accumulation. Effect of acr3 expression on the root transcriptome

Transgenic tobacco hairy roots expressing the bacterial arsenite efflux pump Acr3 from Ensifer medicae were generated. The gene product was targeted either to the plasma membrane (ACR3 lines) or to the tonoplast by fusing the ACR3 protein to the tonoplast integral protein TIP1.1 (TIP-ACR3 lines). Roots expressing Acr3 at the tonoplast showed greater biomass than those expressing Acr3 at the plasma membrane. Furthermore, higher contents of malondialdehyde (MDA) and RNA degradation in ACR3 lines were indicative of higher oxidative stress. The determination of ROS-scavenging enzymes depicted the transient role of peroxidases in ROS detoxification, followed by the action of superoxide dismutase during both short- and medium-term exposure periods. Regarding As accumulation, ACR3 lines accumulated up to 20-30% less As, whereas TIP-ACR3 achieved a 2-fold increase in As accumulation in comparison to control hairy roots. Strategies that presumably induce As uptake, such as phosphate deprivation or dehydration followed by rehydration in the presence of As, fostered As accumulation up to 10 800 μg g-1. Finally, the effects of the heterologous expression of acr3 on the root transcriptome were assessed. Expression at the plasma membrane induced drastic changes in gene expression, with outstanding overexpression of genes related to electron transport, ATP synthesis and ATPases, suggesting that As efflux is the main detoxification mechanism in these lines. In addition, genes encoding heat shock proteins and those related to proline synthesis and drought tolerance were activated. On the other hand, TIP-ACR3 lines showed a similar gene expression profile to that of control roots, with overexpression of the glutathione and phytochelatin synthesis pathways, together with secondary metabolism pathways as the most important resistance mechanisms in TIP-ACR3, for which As allocation into the vacuole allowed better growth and stress management. Our results suggest that modulation of As accumulation can be achieved by subcellular targeting of Acr3: expression at the tonoplast enhances As accumulation in roots, whereas expression at the plasma membrane could promote As efflux. Thus, both approaches open the possibilities for developing safer crops when grown on As-polluted paddy soils, but expression at the tonoplast leads to better growth and less stressed roots, since the high energy cost of As efflux likely compromises growth in ACR3 lines.

Compared to antioxidants and polyamines, the role of maize grain-derived organic biostimulants in improving cadmium tolerance in wheat plants

Recently, the strategy of seed soaking has been successfully applied using extracts from different plant parts for healthy growth of plant under different environmental stresses. Compared to antioxidants like ascorbic acid (AsA) and glutathione (GSH) or polyamines (PAs) like spermine (SPM), spermidine (SPD), and putrescine (PUT), the effects of seed soaking using maize grain extract (MGE) on the biomass, productivity, phytohormones, and antioxidant defense system and its different components were examined with Cd²⁺-stressed wheat plants. In a preliminary study, seed soaking using AsA + GSH or PUT + SPD + SPM was more effective in increasing shoot fresh and dry weights, SPAD chlorophyll, and grain yield, and reducing malondialdehyde (MDA) content than individuals. In addition, MGE at 2% was more efficient than other concentrations. Therefore, they were selected for the main study. In the main study, compared to the control, seed soaking in AsA + GSH, PUT + SPD + SPM or MGE had positive effects on plant growth, yield, photosynthetic efficiency, contents and redox states of AsA and GSH, contents of PAs and plant hormones to varying degrees. Proline content and its metabolism enzymes activity, contents of soluble protein, N-compounds, soluble sugars, and α-tocopherol (α-TOC), and activities of antioxidant enzymes were not affected. However, contents of MDA and hydrogen peroxide (H₂O₂) were significantly reduced under normal conditions. Under Cd²⁺ stress (1.2 mM), along with the detrimental increases in the contents of MDA, H₂O₂ and Cd²⁺, contents of N-compounds, soluble sugars, proline content and its metabolism enzymes activities, AsA and GSH and their redox states, and polyamines, and activities of antioxidant enzymes were increased. In contrast, plant growth and yield, photosynthetic efficiency, soluble protein, and plant hormones were significantly reduced compared to the control. However, all of these attributes were significantly improved to varying degrees along with reduced contents of Cd²⁺, MDA, and H₂O₂ by seed soaking in AsA + GSH, PUT + SPD + SPM or MGE compared to the Cd²⁺-stressed control. Compared to AsA + GSH or PUT + SPD + SPM, seed soaking in MGE at 2% conferred the best results. Therefore, it is recommended to soak wheat seeds using MGE to improve plant growth and productivity by restricting the inhibitory influences of oxidative stress induced by Cd²⁺ stress.

Vitamin C in Plants: From Functions to Biofortification

Vitamin C (l-ascorbic acid) is an excellent free radical scavenger, not only for its capability to donate reducing equivalents but also for the relative stability of the derived monodehydroascorbate radical. However, vitamin C is not only an antioxidant, since it is also a cofactor for numerous enzymes involved in plant and human metabolism. In humans, vitamin C takes part in various physiological processes, such as iron absorption, collagen synthesis, immune stimulation, and epigenetic regulation. Due to the functional loss of the gene coding for l-gulonolactone oxidase, humans cannot synthesize vitamin C; thus, they principally utilize plant-based foods for their needs. For this reason, increasing the vitamin C content of crops could have helpful effects on human health. To achieve this objective, exhaustive knowledge of the metabolism and functions of vitamin C in plants is needed. In this review, the multiple roles of vitamin C in plant physiology as well as the regulation of its content, through biosynthetic or recycling pathways, are analyzed. Finally, attention is paid to the strategies that have been used to increase the content of vitamin C in crops, emphasizing not only the improvement of nutritional value of the crops but also the acquisition of plant stress resistance.

Response of Mustard Microgreens to Different Wavelengths and Durations of UV-A LEDs

Ultraviolet A (UV-A) light-emitting diodes (LEDs) could serve as an effective tool for improving the content of health-promoting bioactive compounds in plants in controlled-environment agriculture (CEA) systems. The goal of this study was to investigate the effects of UV-A LEDs at different wavelengths (366, 390, and 402 nm) and durations (10 and 16 h) on the growth and phytochemical contents of mustard microgreens (Brassica juncea L. cv. "Red Lion"), when used as supplemental light to the main LED lighting system (with peak wavelengths of 447, 638, 665, and 731 nm). Plants were grown for 10 days under a total photon flux density (TPFD) of 300 µmol m^-2 s^-1 and 16-h light/8-h dark period. Different UV-A wavelengths and irradiance durations had varied effects on mustard microgreens. Supplemental UV-A radiation did not affect biomass accumulation; however, the longest UV-A wavelength (402 nm) increased the leaf area of mustard microgreens, regardless of the duration of irradiance. The concentration of the total phenolic content and α-tocopherol mostly increased under 402-nm UV-A, while that of nitrates increased under 366- and 390-nm UV-A at both radiance durations. The contents of lutein/zeaxanthin and β-carotene increased in response to the shortest UV-A wavelength (366 nm) at 10-h irradiance as well as longer UV-A wavelength (390 nm) at 16 h irradiance. The most positive effect on the accumulation of mineral elements, except iron, was observed under longer UV-A wavelengths at 16-h irradiance. Overall, these results suggest that properly composed UV-A LED parameters in LED lighting systems could improve the nutritional quality of mustard microgreens, without causing any adverse effects on plant growth.

Chemical Composition of Mango (Mangifera indica L.) Fruit: Nutritional and Phytochemical Compounds

Mango fruit has a high nutritional value and health benefits due to important components. The present manuscript is a comprehensive update on the composition of mango fruit, including nutritional and phytochemical compounds, and the changes of these during development and postharvest. Mango components can be grouped into macronutrients (carbohydrates, proteins, amino acids, lipids, fatty, and organic acids), micronutrients (vitamins and minerals), and phytochemicals (phenolic, polyphenol, pigments, and volatile constituents). Mango fruit also contains structural carbohydrates such as pectins and cellulose. The major amino acids include lysine, leucine, cysteine, valine, arginine, phenylalanine, and methionine. The lipid composition increases during ripening, particularly the omega-3 and omega-6 fatty acids. The most important pigments of mango fruit include chlorophylls (a and b) and carotenoids. The most important organic acids include malic and citric acids, and they confer the fruit acidity. The volatile constituents are a heterogeneous group with different chemical functions that contribute to the aromatic profile of the fruit. During development and maturity stages occur important biochemical, physiological, and structural changes affecting mainly the nutritional and phytochemical composition, producing softening, and modifying aroma, flavor, and antioxidant capacity. In addition, postharvest handling practices influence total content of carotenoids, phenolic compounds, vitamin C, antioxidant capacity, and organoleptic properties.

Elucidating Drought Stress Tolerance in European Oaks Through Cross-Species Transcriptomics

The impact of climate change that comes with a dramatic increase of long periods of extreme summer drought associated with heat is a fundamental challenge for European forests. As a result, forests are expected to shift their distribution patterns toward north-east, which may lead to a dramatic loss in value of European forest land. Consequently, unraveling key processes that underlie drought stress tolerance is not only of great scientific but also of utmost economic importance for forests to withstand future heat and drought wave scenarios. To reveal drought stress-related molecular patterns we applied cross-species comparative transcriptomics of three major European oak species: the less tolerant deciduous pedunculate oak (Quercus robur), the deciduous but quite tolerant pubescent oak (Q. pubescens), and the very tolerant evergreen holm oak (Q. ilex). We found 415, 79, and 222 differentially expressed genes during drought stress in Q. robur, Q. pubescens, and Q. ilex, respectively, indicating species-specific response mechanisms. Further, by comparative orthologous gene family analysis, 517 orthologous genes could be characterized that may play an important role in drought stress adaptation on the genus level. New regulatory candidate pathways and genes in the context of drought stress response were identified, highlighting the importance of the antioxidant capacity, the mitochondrial respiration machinery, the lignification of the water transport system, and the suppression of drought-induced senescence - providing a valuable knowledge base that could be integrated in breeding programs in the face of climate change.

Differential regulation of defence pathways in aromatic and non-aromatic indica rice cultivars towards fluoride toxicity

Excessive bioaccumulation of fluoride in IR-64 caused low abscisic acid level, inhibition of polyamine biosynthesis and ascorbate-glutathione cycle but not in Gobindobhog which had higher antioxidant activity. The current study presents regulation of diverse metabolic and molecular defence pathways during fluoride stress in non-aromatic rice variety, IR-64 and aromatic rice variety, Gobindobhog (GB). Increasing concentration of fluoride affected fresh weight, dry weight, vigour index and relative water content to a lesser extent in GB compared to IR-64. GB exhibited lower methylglyoxal accumulation and lipoxygenase activity compared to IR-64 during stress. The level of osmolytes (proline, amino acids and glycine-betaine) increased in both the stressed varieties. The biosynthesis of higher polyamines was stimulated in stressed GB. IR-64 accumulated higher amount of putrescine due to degradation of higher polyamines as supported by gene expression analysis. Unlike IR-64, GB efficiently maintained the ascorbate-glutathione cycle due to much lower fluoride bioaccumulation, compared to IR-64. GB adapted to fluoride stress by strongly inducing guaiacol peroxidase, phenylalanine ammonia lyase and a novel isozyme of superoxide dismutase. While GB accumulated higher abscisic acid (ABA) level during stress, IR-64 exhibited slow ABA degradation which enabled induction of associated osmotic stress-responsive genes. Unlike GB, ABA-independent DREB2A was downregulated in stressed IR-64. The research illustrates varietal differences in the defence machinery of the susceptible variety, IR-64, and the well adapted cultivar, GB, on prolonged exposure to increasing concentrations of fluoride.

Alleviation of Phytophthora infestans Mediated Necrotic Stress in the Transgenic Potato (Solanum tuberosum L.) with Enhanced Ascorbic acid Accumulation

Potato is the most widely cultivated non-cereal crop in the world, and like any other crop, it is susceptible to yield losses because of various factors, including pathogen attacks. Among the various diseases of potato, late blight caused by the oomycete Phytophthora infestans is considered as the most devastating disease worldwide. In this study, transgenic potato plants overexpressing the D-galacturonic acid reductase (GalUR) gene with an enhanced level of cellular L-ascorbate (L-AsA) were challenged with Phytophthora infestans to determine the level of stress tolerance induced in those plants. With the onset of pathogen infection, necrotic lesions progressively expanded and became necrotic in the control plants. The transgenic potato lines with enhanced ascorbic acid showed reduced necrotic lesions. Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels were relatively lower in transgenic plants compared to the untransformed control (UT) plants. The mRNA expressions of pathogenesis-related (PR) genes, such as pathogenesis related 1 (PR1) and phenylalanine ammonia-lyase (PAL) were slightly higher in GalUR overexpressing transgenic lines as compared to the untransformed control plants. Pathogen infection also altered the mRNA expression of genes associated with gibberellic acid (GA) and abscisic acid (ABA) biosynthesis. Furthermore, the increase in various antioxidant enzymes was also observed in the gene expression analysis with the transgenic plants. The complete loss of the pathogen growth and disease occurrence was not observed in our study; however, the findings indicated that an increase in the level of cellular L-ascorbate in the transgenic potato leads to enhanced cellular antioxidants, PR genes and plant defense hormones, such as GA and ABA resulting in the reduction of the disease symptoms caused by the Phytophthora infestans.

Regulation of Ascorbate-Glutathione Pathway in Mitigating Oxidative Damage in Plants under Abiotic Stress

Reactive oxygen species (ROS) generation is a usual phenomenon in a plant both under a normal and stressed condition. However, under unfavorable or adverse conditions, ROS production exceeds the capacity of the antioxidant defense system. Both non-enzymatic and enzymatic components of the antioxidant defense system either detoxify or scavenge ROS and mitigate their deleterious effects. The Ascorbate-Glutathione (AsA-GSH) pathway, also known as Asada-Halliwell pathway comprises of AsA, GSH, and four enzymes viz. ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, play a vital role in detoxifying ROS. Apart from ROS detoxification, they also interact with other defense systems in plants and protect the plants from various abiotic stress-induced damages. Several plant studies revealed that the upregulation or overexpression of AsA-GSH pathway enzymes and the enhancement of the AsA and GSH levels conferred plants better tolerance to abiotic stresses by reducing the ROS. In this review, we summarize the recent progress of the research on AsA-GSH pathway in terms of oxidative stress tolerance in plants. We also focus on the defense mechanisms as well as molecular interactions.