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

Pre treatment with Bacillus subtilis mitigates drought induced photo-oxidative damages in okra by modulating antioxidant system and photochemical activity

Growth promoting potential of Bacillus subtilis (BS) in drought stressed Abelmoschus esculentus (L.) Moench (okra) was assessed by measuring the chlorophyll stability index (CSI), chlorophyll a (Chl-a) fluorescence, leaf osmotic potential and lipid peroxidation by malondialdehyde content, emission of reactive oxygen species (ROS), osmolyte content and the activity of non-enzyme and enzyme antioxidants. BS treatment significantly increased the leaf osmotic potential, osmolyte production and the activity of non-enzyme and enzyme antioxidants under drought stress. BS treatment mitigated the drought-induced reduction in Chl a fluorescence and CSI. Concomitant increase in total sugar, proline, non-enzyme antioxidants [glutathione and ascorbate] and enzyme antioxidants like superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase modulate the intracellular ROS concentration in okra to resist the stress induced oxidative damage in BS treated plants led to fast recovery and less photodamage.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00982-8.

Effects of exogenous ascorbic acid on seed germination and seedling salt-tolerance of alfalfa

Alfalfa (Medicago sativa L.) is an important legume crop for forage, agriculture, and environment in the world. Ascorbic acid (AsA) plays positive roles in plants. However, its effects on germination and salt-tolerance of alfalfa are unknown. The effects of AsA applications on seed germination and seedling salt-tolerance of alfalfa were investigated. The results revealed that 0.1 and 1 mmol L^-1 of exogenous AsA increased germination, amylase, and protease, as well as seedling length, fresh weight (FW), dry weight (DW), and endogenous AsA both in the shoots and roots, except that 1 mmol L^-1 AsA reduced the activities of α-amylase, β-amylase and protease on day 3. However, 10 and 100 mmol L^-1 AsA inhibited these parameters and even caused serious rot. It indicates that 0.1 mmol L^-1 AsA has the optimal effects, whereas 100 mmol L^-1 AsA has the worst impacts. Another part of the results showed that 0.1 mmol L^-1 AsA not only enhanced stem elongation, FW and DW, but also increased chlorophyll and carotenoids both under non-stress and 150 mmol L^-1 NaCl stress. Furthermore, 0.1 mmol L^-1 AsA mitigated the damages of membrane permeability, malondialdehyde, and excessive reactive oxygen species (ROS) and ions both in the shoots and roots under 150 mmol L^-1 NaCl stress. Hence, 0.1 mmol L^-1 AsA improves growth and induces salt-tolerance by inhibiting excessive ROS, down-regulating the ion toxicity and up-regulating the antioxidant system. The principal component analysis included two main components both in the shoots and roots, and it explained the results well. In summary, the optimum concentration of 0.1 mmol L^-1 AsA can be implemented to improve the seed germination and seedling growth of alfalfa under salt stress.

Wuxal amino (Bio stimulant) improved growth and physiological performance of tomato plants under salinity stress through adaptive mechanisms and antioxidant potential

In the present study, ameliorative capabilities of wuxal amino (bio stimulant) under salt stress has been investigated through adaptive mechanisms and antioxidant potential in tomato plants. In the experiment, two different concentrations (2 cm L^-1 and 3 cm L^-1) of wuxal amino through foliar application and soil irrigation were applied to the salt (150 mM) treated tomato plants and then morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress and antioxidant enzymes activity were assessed at 60 days after planting. The results revealed that salt stress decreased the growth parameters, photosynthetic pigments, soluble sugars and soluble protein whereas, content of proline, ascorbic acid, total phenols, malondialdehyde, hydrogen peroxide and the activity of antioxidant enzymes activity increased under salt stress. Moreover, Wuxal amino application through foliar or soil to salt stressed plants improved morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Interestingly, the deleterious impact of salinity on tomato plants were significantly reduced and it can be evident from reduced MDA and H₂O₂ levels. These responses varied with the mode (foliar or soil) of application of Wuxal amino under different concentrations (2 cm L^-1 and 3 cm L^-1). It was concluded that application of Wuxal amino (2 cm L^-1, foliar) and (3 cm L^-1; soil) proved best and could be commercially used as eco-friendly tool for the protection of tomato plants grown under salinity stress.

Integrative Analysis of Transcriptome and Metabolome Reveals Salt Stress Orchestrating the Accumulation of Specialized Metabolites in Lycium barbarum L. Fruit

Salt stress seriously affects yield and quality of crops. The fruit of Lycium barbarum (LBF) is extensively used as functional food due to its rich nutrient components. It remains unclear how salt stress influences the quality of LBF. In this study, we identified 71 differentially accumulated metabolites (DAMs) and 1396 differentially expressed genes (DEGs) among ripe LBF with and without 300 mM of NaCl treatment. Pearson correlation analysis indicated that the metabolomic changes caused by salt stress were strongly related to oxidoreductases; hydrolases; and modifying enzymes, in particular, acyltransferases, methyltransferases and glycosyltransferases. Further analysis revealed that salt stress facilitated flavonoid glycosylation and carotenoid esterification by boosting the expression of structural genes in the biosynthetic pathways. These results suggested that salt stress prompts the modification of flavonoids and carotenoids to alleviate ROS damage, which in turn improves the quality of LBF. Our results lay a solid foundation for uncovering the underlying molecular mechanism of salt stress orchestrating LBF quality, and the candidate genes identified will be a valuable gene resource for genetic improvement of L. barbarum.

Silicon Application Modulates Growth, Physio-Chemicals, and Antioxidants in Wheat (Triticum aestivum L.) Exposed to Different Cadmium Regimes

Silicon (Si) application enhanced the tolerance of plants against different environmental stresses. Therefore, objective of the study revealed that foliar applied Si alleviates the adverse effect of Cd by enhancing the growth, metabolite accumulation, strengthening the antioxidant defense system, reducing oxidative injury, improving plant nutrient status, and decreasing the Cd uptake in wheat. The surface sterilized seeds of Sahar-2006 (tolerant) and Inqalab-91 (sensitive) having the differential metal tolerance capacity were sown in plastic pots containing normal and Cd spiked sandy loamy soil. The design of experiments was completely randomized with 3 replicates per treatment. Two weeks after germination, plants were sprayed with different concentrations of Si (1.5 and 3 mM) with 0.1% surfactant in the form of Tween-20. The plants were harvested after 2 weeks of Si application to determine various attributes. High concentration of Cd (25 mg kg-1) decreased growth-related-attributes, essential nutrient uptake and increase the levels of oxidative stress indicators. The application of Si increased the growth-related attributes, photosynthetic pigments, essential nutrient uptake and also enhanced the activities of various antioxidant compounds (superoxide dismutase (SOD), peroxidase (POD, ascorbate peroxidase (APX) and catalase (CAT) by decreasing the contents of oxidative stress indicators and Cd uptake in root and shoot of both wheat cultivars. Sahar-2006 cultivar showed more tolerance to Cd regimes than that of Inqalab-91 as clear from greater plant dry masses. Thus, our results showed that the applied Si level (3 mM) is an efficient strategy for field use in the areas, where slightly Cd polluted soils limit the agriculture production.

Ascorbate oxidation by iron, copper and reactive oxygen species: review, model development, and derivation of key rate constants

Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biological response. Because ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical organic molecule, reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chemistry, but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chemical kinetics model, and use seven sets of laboratory measurements to constrain mechanisms for the iron and copper reactions and derive key rate constants. We find that micromolar concentrations of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH2 and AH-) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II) + AH2/AH-  + O2 → Fe(III)/Cu(II) + H2O2 + products. Rate constants are 5.7 × 104 and 4.7 × 104 M-2 s-1 for Fe(III) + AH2/AH- and 7.7 × 104 and 2.8 × 106 M-2 s-1 for Cu(II) + AH2/AH-, respectively.

Experimental and theoretical study on the hydrogen bond interactions between ascorbic acid and glycine

Cyclic voltammetry, 1H nuclear magnetic resonance and quantum chemistry calculations were applied to explore the hydrogen bond interactions between ascorbic acid (AA) and glycine. The experimental results demonstrate the existence of hydrogen bonds in AA-glycine system, which has a significant effect on the oxidation peak potentials and currents of AA and the chemical shifts of glycine. The formation of hydrogen bonds between AA and glycine were further confirmed by the density functional theory, quantum theory of atoms in molecules and natural bond orbital analyses.

Proteomic profiling of human uterine extracellular vesicles reveal dynamic regulation of key players of embryo implantation and fertility during menstrual cycle

Endometrial extracellular vesicles (EVs) are emerging as important players in reproductive biology. However, how their proteome is regulated throughout the menstrual cycle is not known. Such information can provide novel insights into biological processes critical for embryo development, implantation, and successful pregnancy. Using mass spectrometry-based quantitative proteomics, we show that small EVs (sEVs) isolated from uterine lavage of fertile women (UL-sEV), compared to infertile women, are laden with proteins implicated in antioxidant activity (SOD1, GSTO1, MPO, CAT). Functionally, sEVs derived from endometrial cells enhance antioxidant function in trophectoderm cells. Moreover, there was striking enrichment of invasion-related proteins (LGALS1/3, S100A4/11) in fertile UL-sEVs in the secretory (estrogen plus progesterone-driven, EP) versus proliferative (estrogen-driven, E) phase, with several players downregulated in infertile UL-sEVs. Consistent with this, sEVs from EP- versus E-primed endometrial epithelial cells promote invasion of trophectoderm cells. Interestingly, UL-sEVs from fertile versus infertile women carry known players/predictors of embryo implantation (PRDX2, IDHC), endometrial receptivity (S100A4, FGB, SERPING1, CLU, ANXA2), and implantation success (CAT, YWHAE, PPIA), highlighting their potential to inform regarding endometrial status/pregnancy outcomes. Thus, this study provides novel insights into proteome reprograming of sEVs and soluble secretome in uterine fluid, with potential to enhance embryo implantation and hence fertility.

Fullerenol regulates oxidative stress and tissue ionic homeostasis in spring wheat to improve net-primary productivity under salt-stress

The effects of fullerenol nanopriming (0, 10, 40, 80 and 120 nM concentration) on salt stressed-wheat (0 and 150 mM NaCl) were investigated under natural conditions. Salinity resulted in a shift in wheat growth pattern in the form of LAR (+ 40.9% increase) and RGR (+ 13.4% increase) while decreased NAR (- 31.7%). It also disturbed shoot and root biomass, ion uptake and reduced chlorophyll contents. Despite increase in enzyme activities, higher ROS generation (+ 48.1% O₂^- anion; and + 62.2% H₂O₂) and lipid peroxidation (+ 40.8% MDA) were detected in salt-stressed wheat plants. Possibly, the increases in enzyme activities were not up to the level to completely counteract the salinity induced oxidative stress. Nanopriming with fullerenol improved NAR (+ 8.77% to 23.2%), ROS metabolism and decreased indicators of oxidative stress. Hydropriming treatment also promoted NAR recovery by 21.9% than control plants. Compared to Na⁺ ions, improvements in shoot relative concentrations of K⁺, Ca²⁺ and P also recorded along with soluble sugars and amino acids, which improved osmotic balance. These biochemical modifications contributed to improvements in grain yield attributes (+11.8% to 18.3% in 100 grain-weight) than salinity stressed control. Hydropriming also contributed to a recovery in grain yield attributes by 12.6%. Above all, the harvested seeds from fullerenol treated plants also showed better germination and seedlings growth traits. Conclusively, we report non-toxic, growth-promoting effects of fullerenol nanoparticles on wheat crop and as a way forward; we suggest its exogenous application to recover crop productivity under saline environments.

Sustainable Processing of Floral Bio-Residues of Saffron (Crocus sativus L.) for Valuable Biorefinery Products

Tepals constitute the most abundant bio-residues of saffron (Crocus sativus L.). As they are a natural source of polyphenols with antioxidant properties, they could be processed to generate valuable biorefinery products for applications in the pharmaceutical, cosmetic, and food industries, becoming a new source of income while reducing bio-waste. Proper storage of by-products is important in biorefining and dehydration is widely used in the herb sector, especially for highly perishable harvested flowers. This study aimed to deepen the phytochemical composition of dried saffron tepals and to investigate whether this was influenced by the extraction technique. In particular, the conventional maceration was compared with the Ultrasound Assisted Extraction (UAE), using different solvents (water and three methanol concentrations, i.e., 20%, 50%, and 80%). Compared to the spice, the dried saffron tepals showed a lower content of total phenolics (average value 1127.94 ± 32.34 mg GAE 100 g⁻¹ DW) and anthocyanins (up to 413.30 ± 137.16 mg G3G 100 g⁻¹ DW), but a higher antioxidant activity, which was measured through the FRAP, ABTS, and DPPH assays. The HPLC-DAD analysis detected some phenolic compounds (i.e., ferulic acid, isoquercitrin, and quercitrin) not previously found in fresh saffron tepals. Vitamin C, already discovered in the spice, was interestingly detected also in dried tepals. Regarding the extraction technique, in most cases, UAE with safer solvents (i.e., water or low percentage of methanol) showed results of phenolic compounds and vitamin C similar to maceration, allowing an improvement in extractions by halving the time. Thus, this study demonstrated that saffron tepals can be dried maintaining their quality and that green extractions can be adopted to obtain high yields of valuable antioxidant phytochemicals, meeting the requirement for a sustainable biorefining.

The Relationship between the Antioxidant System and Proline Metabolism in the Leaves of Cucumber Plants Acclimated to Salt Stress

The study examines the effect of acclimation on the antioxidant system and proline metabolism in cucumber leaves subjected to 100 and 150 NaCl stress. The levels of protein carbonyl group, thiobarbituric acid reactive substances, α-tocopherol, and activity of ascorbate and glutathione peroxidases, catalase, glutathione S-transferase, pyrroline-5-carboxylate: synthetase and reductase as well as proline dehydrogenase were determined after 24 and 72 h periods of salt stress in the acclimated and non-acclimated plants. Although both groups of plants showed high α-tocopherol levels, in acclimated plants was observed higher constitutive concentration of these compounds as well as after salt treatment. Furthermore, the activity of enzymatic antioxidants grew in response to salt stress, mainly in the acclimated plants. In the acclimated plants, protein carbonyl group levels collapsed on a constitutive level and in response to salt stress. Although both groups of plants showed a decrease in proline dehydrogenase activity, they differed with regard to the range and time. Differences in response to salt stress between the acclimated and non-acclimated plants may suggest a relationship between increased tolerance in acclimated plants and raised activity of antioxidant enzymes, high-level of α-tocopherol as well, as decrease enzyme activity incorporates in proline catabolism.

Comparative transcriptome and metabolome profiling reveal molecular mechanisms underlying OsDRAP1-mediated salt tolerance in rice

Integration of transcriptomics and metabolomics data can provide detailed information for better understanding the molecular mechanisms underlying salt tolerance in rice. In the present study, we report a comprehensive analysis of the transcriptome and metabolome of rice overexpressing the OsDRAP1 gene, which encodes an ERF transcription factor and was previously identified to be conferring drought tolerance. Phenotypic analysis showed that OsDRAP1 overexpression (OE) improved salt tolerance by increasing the survival rate under salt stress. OsDRAP1 affected the physiological indices such as superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) to enhance redox homeostasis and membrane stability in response to salt stress. Higher basal expression of OsDRAP1 resulted in differential expression of genes that potentially function in intrinsic salt tolerance. A core set of genes with distinct functions in transcriptional regulation, organelle gene expression and ion transport were substantially up-regulated in the OE line in response to salt stress, implying their important role in OsDRAP1-mediated salt tolerance. Correspondingly, metabolome profiling detected a number of differentially metabolites in the OE line relative to the wild type under salt stress. These metabolites, including amino acids (proline, valine), organic acids (glyceric acid, phosphoenolpyruvic acid and ascorbic acid) and many secondary metabolites, accumulated to higher levels in the OE line, demonstrating their role in salt tolerance. Integration of transcriptome and metabolome analysis highlights the crucial role of amino acids and carbohydrate metabolism pathways in OsDRAP1-mediated salt tolerance.

Kaolin Application Modulates Grapevine Photochemistry and Defence Responses in Distinct Mediterranean-Type Climate Vineyards

At a local scale, kaolin particle-film technology is considered a short-term adaptation strategy to mitigate the adverse effects of global warming on viticulture. This study aims to evaluate kaolin application effects on photochemistry and related defence responses of Touriga Franca (TF) and Touriga Nacional (TN) grapevines planted at two Portuguese winegrowing regions (Douro and Alentejo) over two summer seasons (2017 and 2018). For this purpose, chlorophyll a fluorescence transient analysis, leaf temperature, foliar metabolites, and the expression of genes related to heat stress (VvHSP70) and stress tolerance (VvWRKY18) were analysed. Kaolin application had an inhibitory effect on VvHSP70 expression, reinforcing its protective role against heat stress. However, VvWRKY18 gene expression and foliar metabolites accumulation revealed lower gene expression in TN-treated leaves and higher in TF at Alentejo, while lipid peroxidation levels decreased in both treated varieties and regions. The positive kaolin effect on the performance index parameter (PIABS) increased at ripening, mainly in TN, suggesting that stress responses can differ among varieties, depending on the initial acclimation to kaolin treatment. Moreover, changes on chlorophyll fluorescence transient analysis were more pronounced at the Douro site in 2017, indicating higher stress severity and impacts at this site, which boosted kaolin efficiency in alleviating summer stress. Under applied contexts, kaolin application can be considered a promising practice to minimise summer stress impacts in grapevines grown in Mediterranean-like climate regions.

Differential Morpho-Physiological and Transcriptomic Responses to Heat Stress in Two Blueberry Species

Blueberries (Vaccinium spp.) are highly vulnerable to changing climatic conditions, especially increasing temperatures. To gain insight into mechanisms underpinning the response to heat stress, two blueberry species were subjected to heat stress for 6 and 9 h at 45 °C, and leaf samples were used to study the morpho-physiological and transcriptomic changes. As compared with Vaccinium corymbosum, Vaccinium darrowii exhibited thermal stress adaptation features such as small leaf size, parallel leaf orientation, waxy leaf coating, increased stomatal surface area, and stomatal closure. RNAseq analysis yielded ~135 million reads and identified 8305 differentially expressed genes (DEGs) during heat stress against the control samples. In V. corymbosum, 2861 and 4565 genes were differentially expressed at 6 and 9 h of heat stress, whereas in V. darrowii, 2516 and 3072 DEGs were differentially expressed at 6 and 9 h, respectively. Among the pathways, the protein processing in the endoplasmic reticulum (ER) was the highly enriched pathway in both the species: however, certain metabolic, fatty acid, photosynthesis-related, peroxisomal, and circadian rhythm pathways were enriched differently among the species. KEGG enrichment analysis of the DEGs revealed important biosynthesis and metabolic pathways crucial in response to heat stress. The GO terms enriched in both the species under heat stress were similar, but more DEGs were enriched for GO terms in V. darrowii than the V. corymbosum. Together, these results elucidate the differential response of morpho-physiological and molecular mechanisms used by both the blueberry species under heat stress, and help in understanding the complex mechanisms involved in heat stress tolerance.

Responses of Phragmites australis to copper stress: A combined analysis of plant morphology, physiology and proteomics

Few relevant research attempts have been made to determine heavy metal resistance mechanisms of rhizomatous perennial plants. Thus, it is pertinent to investigate the physiological and biochemical changes in Phragmites australis under metal-stressed conditions to facilitate the development of strategies to enhance copper (Cu) tolerance. We measured parameters related to plant growth and development, metal translocation and physiological responses of P. australis subjected to Cu stress. In addition, the differentially expressed proteins (DEP) were evaluated using the isobaric tag for relative and absolute quantification (iTRAQ) system. A large amount of copper accumulates in the roots of P.australis, but the growth parameters were not sensitive to Cu. However, the high concentration of Cu reduced the content of chlorophyll a and chlorophyll b, and the expression of important photosynthesis proteins PsbD, PsbO and PsaA were all down-regulated, so photosynthesis was inhibited. In contrast, the content of ascorbic acid and proline both increased with the increase of copper stress. P.australis fixed a large amount of Cu in its roots, limiting the migration of Cu to other parts of the plant. Moreover, Cu stress can affect photosynthesis by inhibiting the activity of PSI, PSII and LHCII. In addition, P.australis synthesizes ascorbic acid through the D-mannose/L-galactose pathway, and synthesizes proline through the ornithine pathway. Ascorbic acid and proline can increase Cu tolerance and protect photosynthesis. These results provide a theoretical basis for understanding the tolerance and repair mechanisms of plants in response to heavy metal pollution.

Silver nanoparticles improved the plant growth and reduced the sodium and chlorine accumulation in pearl millet: a life cycle study

Salt stress in agricultural soils is a global issue and little information is available about the efficiency of silver nanoparticles (AgNPs) in plants under salt stress. The aim of current study was to assess the efficacy of AgNPs in improving plant growth and reducing the salt-induced damages in pearl millet. The exposure of pearl millet plants grown in pots containing soil to different doses of salinity (0, 120, 150 mM) and AgNPs (0, 10, 20 and 30 mM) significantly influenced the morphology, physiology and yield-related attributes. Salt stress remarkably increased the concentration of sodium (Na) and chloride (Cl) in different organs of pearl millet plants. This led to increase the enhancement of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content and caused severe oxidative damage by augmenting the activities of antioxidant enzymes. The obvious decrease in plant growth, height, dry biomass of root and shoot, chlorophylls and carotenoid contents was observed in salt-stressed plants which ultimately reduced the yield of plants. The AgNPs remarkably improved the plant growth by reducing oxidative stress and Na and Cl uptake by salt-stressed plants. The AgNPs were also found to maintain the ionic balance of cell (Na⁺, K⁺ and Na⁺/K⁺ ratio). The AgNPs improved the superoxide dismutase, catalase activities and decreased the peroxidase activity while reduced the H₂O₂ and MDA contents in plants under salt stress. Overall, AgNPs increased the plant height, yield, and photosynthesis of salt-stressed plants in a dose-additive manner.

Ascorbic acid modulation by ABI4 transcriptional repression of VTC2 in the salt tolerance of Arabidopsis

BACKGROUND

Abscisic acid (ABA) plays an important role in plant abiotic stress responses, and ABA INSENSITIVE 4 (ABI4) is a pivotal transcription factor in the ABA signaling pathway. In Arabidopsis, ABI4 negatively regulates salt tolerance; however, the mechanism through which ABI4 regulates plant salt tolerance is poorly understood. Our previous study showed that ABI4 directly binds to the promoter of the VITAMIN C DEFECTIVE 2 (VTC2) gene, inhibiting the transcription of VTC2 and ascorbic acid (AsA) biosynthesis.

RESULTS

In the present study, we found that treatment with exogenous AsA could alleviate salt stress sensitivity of ABI4-overexpressing transgenic plants. The decreased AsA content and increased reactive oxygen species (ROS) levels in ABI4-overexpressing seedlings under salt treatment indicated that AsA-promoted ROS scavenging was related to ABI4-mediated salt tolerance. Gene expression analysis showed that ABI4 was induced at the early stage of salt stress, giving rise to reduced VTC2 expression. Accordingly, the abundance of the VTC2 protein decreased under the same salt stress conditions, and was absent in the ABI4 loss-of-function mutants, suggesting that the transcriptional inhibition of ABI4 on VTC2 resulted in the attenuation of VTC2 function. In addition, other encoding genes in the AsA biosynthesis and recycling pathways showed different responses to salt stress, demonstrating that AsA homeostasis is complicated under salinity stress.

CONCLUSIONS

This study elucidates the negative modulation of ABI4 in salt stress tolerance through the regulation of AsA biosynthesis and ROS accumulation in plants.

Impact of Foliar Application of Chitosan Dissolved in Different Organic Acids on Isozymes, Protein Patterns and Physio-Biochemical Characteristics of Tomato Grown under Salinity Stress

In this study, the anti-stress capabilities of the foliar application of chitosan, dissolved in four different organic acids (acetic acid, ascorbic acid, citric acid and malic acid) have been investigated on tomato (Solanum lycopersicum L.) plants under salinity stress (100 mM NaCl). Morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress, minerals, antioxidant enzymes activity, isozymes and protein patterns were tested for potential tolerance of tomato plants growing under salinity stress. Salinity stress was caused a reduction in growth parameters, photosynthetic pigments, soluble sugars, soluble proteins and potassium (K⁺) content. However, the contents of proline, ascorbic acid, total phenol, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), sodium (Na⁺) and antioxidant enzyme activity were increased in tomato plants grown under saline conditions. Chitosan treatments in any of the non-stressed plants showed improvements in morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Besides, the harmful impacts of salinity on tomato plants have also been reduced by lowering MDA, H₂O₂ and Na⁺ levels. Chitosan treatments in either non-stressed or stressed plants showed different responses in number and density of peroxidase (POD), polyphenol oxidase (PPO) and superoxide dismutase (SOD) isozymes. NaCl stress led to the diminishing of protein bands with different molecular weights, while they were produced again in response to chitosan foliar application. These responses were varied according to the type of solvent acid. It could be suggested that foliar application of chitosan, especially that dissolved in ascorbic or citric acid, could be commercially used for the stimulation of tomato plants grown under salinity stress.

Stress response and tolerance to perfluorooctane sulfonate (PFOS) in lettuce (Lactuca sativa)

Comprehensive understanding of stress response and tolerance to perfluorooctane sulfonate (PFOS) in plants at physiological, biochemical and molecular levels is scarce. Here, lettuce was cultivated in hydroponic media, to investigate the cross-talk among reactive oxygen species (ROS) production, oxidative damage, antioxidative defense and metabolic regulation in different parts of plants. Under exposure to 5 and 50 μg/L PFOS for 10 days, 8.8 and 82.5 ng/g dry weight (dw) PFOS were accumulated in leaves, respectively, and 150.9 and 1445.6 ng/g dw in roots, respectively·H2O2 was the dominant ROS in roots, while H2O2 and •O2- were detected in leaves. Impaired permeability of plasma membrane (58.7-88.7%, p < 0.05) and reduction in chlorophyll a (41.4-55.6%, p < 0.01) and b (38.4-41.3%, p < 0.01) were observed in leaves. The concentration of soluble proteins was elevated by 93.2-127.4% in roots (p < 0.05). Non-enzymatic antioxidants (glutathione, phenolics and carotenoids) were regulated to scavenge ROS in leaves, beside additional enzymatic antioxidants (ascorbate peroxidase, peroxidase, catalase and glutathione peroxidase) were activated in roots. Metabolomics revealed that some metabolites in primary (amino acids and carbohydrates) and secondary ((poly)phenols, terpenoids and benzylisoquinolines) metabolism were regulated, in accordance with the ROS scavenging process in plants. Our results demonstrated stress response and tolerance to PFOS were different in lettuce leaves and roots, and multiple defensive mechanisms in roots rendered high tolerance to PFOS.

Screening and Genetic Network Analysis of Genes Involved in Freezing and Thawing Resistance in DaMDHAR-Expressing Saccharomyces cerevisiae Using Gene Expression Profiling

The cryoprotection of cell activity is a key determinant in frozen-dough technology. Although several factors that contribute to freezing tolerance have been reported, the mechanism underlying the manner in which yeast cells respond to freezing and thawing (FT) stress is not well established. Therefore, the present study demonstrated the relationship between DaMDHAR encoding monodehydroascorbate reductase from Antarctic hairgrass Deschampsia antarctica and stress tolerance to repeated FT cycles (FT2) in transgenic yeast Saccharomyces cerevisiae. DaMDHAR-expressing yeast (DM) cells identified by immunoblotting analysis showed high tolerance to FT stress conditions, thereby causing lower damage for yeast cells than wild-type (WT) cells with empty vector alone. To detect FT2 tolerance-associated genes, 3′-quant RNA sequencing was employed using mRNA isolated from DM and WT cells exposed to FT (FT2) conditions. Approximately 332 genes showed ≥2-fold changes in DM cells and were classified into various groups according to their gene expression. The expressions of the changed genes were further confirmed using western blot analysis and biochemical assay. The upregulated expression of 197 genes was associated with pentose phosphate pathway, NADP metabolic process, metal ion homeostasis, sulfate assimilation, β-alanine metabolism, glycerol synthesis, and integral component of mitochondrial and plasma membrane (PM) in DM cells under FT2 stress, whereas the expression of the remaining 135 genes was partially related to protein processing, selenocompound metabolism, cell cycle arrest, oxidative phosphorylation, and α-glucoside transport under the same condition. With regard to transcription factors in DM cells, MSN4 and CIN5 were activated, but MSN2 and MGA1 were not. Regarding antioxidant systems and protein kinases in DM cells under FT stress, CTT1, GTO, GEX1, and YOL024W were upregulated, whereas AIF1, COX2, and TRX3 were not. Gene activation represented by transcription factors and enzymatic antioxidants appears to be associated with FT2-stress tolerance in transgenic yeast cells. RCK1, MET14, and SIP18, but not YPK2, have been known to be involved in the protein kinase-mediated signalling pathway and glycogen synthesis. Moreover, SPI18 and HSP12 encoding hydrophilin in the PM were detected. Therefore, it was concluded that the genetic network via the change of gene expression levels of multiple genes contributing to the stabilization and functionality of the mitochondria and PM, not of a single gene, might be the crucial determinant for FT tolerance in DaMDAHR-expressing transgenic yeast. These findings provide a foundation for elucidating the DaMDHAR-dependent molecular mechanism of the complex functional resistance in the cellular response to FT stress.

Alleviatory effects of Silicon on the morphology, physiology, and antioxidative mechanisms of wheat (Triticum aestivum L.) roots under cadmium stress in acidic nutrient solutions

Silicon (Si), as a quasi-essential element, has a vital role in alleviating the damaging effects of various environmental stresses on plants. Cadmium (Cd) stress is severe abiotic stress, especially in acidic ecological conditions, and Si can demolish the toxicity induced by Cd as well as acidic pH on plants. Based on these hypotheses, we demonstrated 2-repeated experiments to unfold the effects of Si as silica gel on the root morphology and physiology of wheat seedling under Cd as well as acidic stresses. For this purpose, we used nine treatments with three levels of Si nanoparticles (0, 1, and 3 mmol L⁻¹) derived from sodium silicate (Na₂SiO₃) against three concentrations of Cd (0, 50, and 200 µmol L⁻¹) in the form of cadmium chloride (CdCl₂) with three replications were arranged in a complete randomized design. The pH of the nutrient solution was adjusted at 5. The averages of three random replications showed that the mutual impacts of Si and Cd in acidic pH on wheat roots depend on the concentrations of Si and Cd. The collective or particular influence of low or high levels of Si (1 or 3 mM) and acidic pH (5) improved the development of wheat roots, and the collective influence was more significant than that of a single parallel treatment. The combined effects of low or high concentrations of Cd (50 or 200 µM) and acidic pH significantly reduced root growth and biomass while increased antioxidants, and reactive oxygen species (ROS) contents. The incorporation of Si (1 or 3 mmol L⁻¹) in Cd-contaminated acidic nutrient solution promoted the wheat root growth, decreased ROS contents, and further increased the antioxidants in the wheat roots compared with Cd single treatments in acidic pH. The demolishing effects were better with a high level of Si (3 mM) than the low level of Si (1 Mm). In conclusion, we could suggest Si as an effective beneficial nutrient that could participate actively in several morphological and physiological activities of roots in wheat plants grown under Cd and acidic pH stresses.

Bioregulators: unlocking their potential role in regulation of the plant oxidative defense system

Plant bioregulators play an important role in managing oxidative stress tolerance in plants. Utilizing their ability in stress sensitive crops through genetic engineering will be a meaningful approach to manage food production under the threat of climate change. Exploitation of the plant defense system against oxidative stress to engineer tolerant plants in the climate change scenario is a sustainable and meaningful strategy. Plant bioregulators (PBRs), which are important biotic factors, are known to play a vital role not only in the development of plants, but also in inducing tolerance in plants against various environmental extremes. These bioregulators include auxins, gibberellins, cytokinins, abscisic acid, brassinosteroids, polyamines, strigolactones, and ascorbic acid and provide protection against the oxidative stress-associated reactive oxygen species through modulation or activation of a plant's antioxidant system. Therefore, exploitation of their functioning and accumulation is of considerable significance for the development of plants more tolerant of harsh environmental conditions in order to tackle the issue of food security under the threat of climate change. Therefore, this review summarizes a new line of evidence that how PBRs act as inducers of oxidative stress resistance in plants and how they could be modulated in transgenic crops via introgression of genes. Reactive oxygen species production during oxidative stress events and their neutralization through an efficient antioxidants system is comprehensively detailed. Further, the use of exogenously applied PBRs in the induction of oxidative stress resistance is discussed. Recent advances in engineering transgenic plants with modified PBR gene expression to exploit the plant defense system against oxidative stress are discussed from an agricultural perspective.

The Multiple Roles of Ascorbate in the Abiotic Stress Response of Plants: Antioxidant, Cofactor, and Regulator

Ascorbate (ASC) plays a critical role in plant stress response. The antioxidant role of ASC has been well-studied, but there are still several confusing questions about the function of ASC in plant abiotic stress response. ASC can scavenge reactive oxygen species (ROS) and should be helpful for plant stress tolerance. But in some cases, increasing ASC content impairs plant abiotic stress tolerance, whereas, inhibiting ASC synthesis or regeneration enhances plant stress tolerance. This confusing phenomenon indicates that ASC may have multiple roles in plant abiotic stress response not just as an antioxidant, though many studies more or less ignored other roles of ASC in plant. In fact, ACS also can act as the cofactor of some enzymes, which are involved in the synthesis, metabolism, and modification of a variety of substances, which has important effects on plant stress response. In addition, ASC can monitor and effectively regulate cell redox status. Therefore, we believe that ASC has atleast triple roles in plant abiotic stress response: as the antioxidant to scavenge accumulated ROS, as the cofactor to involve in plant metabolism, or as the regulator to coordinate the actions of various signal pathways under abiotic stress. The role of ASC in plant abiotic stress response is important and complex. The detail role of ASC in plant abiotic stress response should be analyzed according to specific physiological process in specific organ. In this review, we discuss the versatile roles of ASC in the response of plants to abiotic stresses.

Ascorbic Acid-Induced Photosynthetic Adaptability of Processing Tomatoes to Salt Stress Probed by Fast OJIP Fluorescence Rise

In this study, the protective role of exogenous ascorbic acid (AsA) on salt-induced inhibition of photosynthesis in the seedlings of processing tomatoes under salt stress has been investigated. Plants under salt stress (NaCl, 100 mmol/L) were foliar-sprayed with AsA (0.5 mmol/L), lycorine (LYC, 0.25 mmol/L, an inhibitor of key AsA synthesis enzyme l-galactono-γ-lactone dehydrogenase activity), or AsA plus LYC. The effects of AsA on fast OJIP fluorescence rise curve and JIP parameters were then examined. Our results demonstrated that applying exogenous AsA significantly changed the composition of O-J-I-P fluorescence transients in plants subjected to salt stress both with and without LYC. An increase in basal fluorescence (F _o) and a decrease in maximum fluorescence (F _m) were observed. Lower K- and L-bands and higher I-band were detected on the OJIP transient curves compared, respectively, with salt-stressed plants with and without LYC. AsA application also significantly increased the values of normalized total complementary area (S_m), relative variable fluorescence intensity at the I-step (V_I), absorbed light energy (ABS/CS_m), excitation energy (TR_o/CS_m), and reduction energy entering the electron transfer chain beyond Q_A (ET_o/CS_m) per reaction centre (RC) and electron transport flux per active RC (ET_o/RC), while decreasing some others like the approximated initial slope of the fluorescence transient (M_o), relative variable fluorescence intensity at the K-step (V_K), average absorption (ABS/RC), trapping (TR_o/RC), heat dissipation (DI_o/RC) per active RC, and heat dissipation per active RC (DI_o/CS_m) in the presence or absence of LYC. These results suggested that exogenous AsA counteracted salt-induced photoinhibition mainly by modulating the endogenous AsA level and redox state in the chloroplast to promote chlorophyll synthesis and alleviate the damage of oxidative stress to photosynthetic apparatus. AsA can also raise the efficiency of light utilization as well as excitation energy dissipation within the photosystem II (PSII) antennae, thus increasing the stability of PSII and promoting the movement of electrons among PS1 and PSII in tomato seedling leaves subjected to salt stress.

A Metabolomic Landscape of Maize Plants Treated With a Microbial Biostimulant Under Well-Watered and Drought Conditions

Microbial plant biostimulants have been successfully applied to improve plant growth, stress resilience and productivity. However, the mechanisms of action of biostimulants are still enigmatic, which is the main bottleneck for the fully realization and implementation of biostimulants into the agricultural industry. Here, we report the elucidation of a global metabolic landscape of maize (Zea mays L) leaves in response to a microbial biostimulant, under well-watered and drought conditions. The study reveals that the increased pool of tricarboxylic acid (TCA) intermediates, alterations in amino acid levels and differential changes in phenolics and lipids are key metabolic signatures induced by the application of the microbial-based biostimulant. These reconfigurations of metabolism gravitate toward growth-promotion and defense preconditioning of the plant. Furthermore, the application of microbial biostimulant conferred enhanced drought resilience to maize plants via altering key metabolic pathways involved in drought resistance mechanisms such as the redox homeostasis, strengthening of the plant cell wall, osmoregulation, energy production and membrane remodeling. For the first time, we show key molecular events, metabolic reprogramming, activated by a microbial biostimulant for plant growth promotion and defense priming. Thus, these elucidated metabolomic insights contribute to ongoing efforts in decoding modes of action of biostimulants and generating fundamental scientific knowledgebase that is necessary for the development of the plant biostimulants industry, for sustainable food security.

Maize bHLH55 functions positively in salt tolerance through modulation of AsA biosynthesis by directly regulating GDP-mannose pathway genes

Ascorbic acid (AsA) is an antioxidant and enzyme co-factor that is vital to plant development and abiotic stress tolerance. However, the regulation mechanisms of AsA biosynthesis in plants remain poorly understood. Here, we report a basic helix-loop-helix 55 (ZmbHLH55) transcription factor that regulates AsA biosynthesis in maize. Analysis of publicly available transcriptomic data revealed that ZmbHLH55 is co-expressed with several genes of the GDP-mannose pathway. Experimental data showed that ZmbHLH55 forms homodimers localized to the cell nuclei, and it exhibits DNA binding and transactivation activity in yeast. Under salt stress conditions, knock down mutant (zmbhlh55) in maize accumulated lower levels of AsA compared with wild type, accompanied by lower antioxidant enzymes activity, shorter root length, and higher malondialdehyde (MDA) level. Gene expression data from the WT and zmbhlh55 mutant, showed that ZmbHLH55 positively regulates the expression of ZmPGI2, ZmGME1, and ZmGLDH, but negatively regulates ZmGMP1 and ZmGGP. Furthermore, ZmbHLH55-overexpressing Arabidopsis, under salt conditions, showed higher AsA levels, increased rates of germination, and elevated antioxidant enzyme activities. In conclusion, these results have identified previously unknown regulation mechanisms for AsA biosynthesis, indicating that ZmbHLH55 may be a potential candidate to enhance plant salt stress tolerance in the future.

Pure Organic Active Compounds Against Abiotic Stress: A Biostimulant Overview

Biostimulants (BSs) are probably one of the most promising alternatives nowadays to cope with yield losses caused by plant stress, which are intensified by climate change. Biostimulants comprise many different compounds with positive effects on plants, excluding pesticides and chemical fertilisers. Usually mixtures such as lixiviates from proteins or algal extracts have been used, but currently companies are interested in more specific compounds that are capable of increasing tolerance against abiotic stress. Individual application of a pure active compound offers researchers the opportunity to better standarise formulations, learn more about the plant defence process itself and assist the agrochemical industry in the development of new products. This review attempts to summarise the state of the art regarding various families of organic compounds and their mode/mechanism of action as BSs, and how they can help maximise agricultural yields under stress conditions aggravated by climate change.

Glycinebetaine-Induced Alteration in Gaseous Exchange Capacity and Osmoprotective Phenomena in Safflower (Carthamus tinctorius L.) under Water Deficit Conditions

Several inorganic and organic compounds including glycine betaine (GB) are presently being used as an exogenous application to enhance tolerance in plants to different environmental stresses. The current study assessed to what extent exogenously applied GB could improve the gaseous exchange capacity and primary and secondary metabolites in two accessions (16178 and 16180) of safflower (Carthamus tinctorius L.) plants under drought stress. Three-week-old plants of both safflower accessions were subjected to well-watered (control) or water-deficit conditions (60% field capacity (FC)). Three levels of GB (control, 50 mM and 100 mM) were sprayed to the foliage of the control and stressed plants after one month of drought application. After two weeks of foliar application of GB, gas exchange characteristics and other biochemical parameters were determined. The results showed that water deficiency markedly suppressed plant biomass, chlorophyll contents, photosynthesis rate (A), water use efficiency (A/E), stomatal conductance (gs) and relative water contents (RWC) of both accessions of safflower, while it enhanced the levels of osmolytes (GB and proline), hydrogen peroxide (H2O2) and total phenolics. Foliar application of GB was effective in enhancing the plant biomass, chlorophyll contents, gs, sub-stomatal CO2 concentration (Ci), Ci/Ca ratio, osmolytes, H2O2, ascorbic acid (AsA), total phenolics and RWC in safflower plants under water shortage. Thus, exogenous application of GB could be used as an effective strategy to improve plant growth, photosynthetic attributes and secondary metabolites in safflower plants under water deficit conditions.

Carotenoids, Vitamin C, and Antioxidant Capacity in the Peel of Mandarin Fruit in Relation to the Susceptibility to Chilling Injury during Postharvest Cold Storage

Chilling injury (CI) is a postharvest disorder occurring in the fruit of cold-sensitive Citrus species during storage at low temperatures. This study investigated the involvement of carotenoids and vitamin C, two major antioxidants of citrus peel, and the antioxidant capacity in the CI susceptibility of mandarin fruit. To that end, the fruit of three commercial varieties, Fortune, Nova, and Nadorcott, with significant differences in CI susceptibility, were selected. By on-tree fruit bagging, carotenoids and vitamin C contents were modified, and a differential effect of each cultivar on CI was observed. Carotenoid analysis in the peel revealed a strong negative correlation between total carotenoid concentration (TCC) at harvest, and specifically of β-cryptoxanthin and violaxanthin, and CI index at the end of storage. In contrast, vitamin C content was significantly and positively correlated with CI susceptibility. The antioxidant activity assessed by the DPPH• and FRAP reflected the contribution of vitamin C to the antioxidant system, while the SOAC assay correlated positively with TTC, β-cryptoxanthin, and violaxanthin. Collectively, the antioxidant capacity of carotenoids at harvest, as efficient singlet oxygen quenchers, suggests a protective role against the development of CI in mandarin fruit, while vitamin C is not likely playing a critical role.

Response of Vallisneria natans to aluminum phytotoxicity and their synergistic effect on nitrogen, phosphorus change in sediments

Increasing aluminum (Al) use and its effects on aquatic systems have been a global issue, however the Al impacts on submerged plants and their ecological functions were poorly understood. Aquatic simulation experiments were performed to study Al-toxicity on the germination and seedling morphological and physiological characteristics of Vallisneria natans, and investigate their synergistic effect on nitrogen (N), phosphorus (P) change and microbial community in sediment. The seeds germination characteristics, growth and physiological parameters of seedlings, including root activity, were significantly affected by alum treatments and the inhibition levels increased with Al³⁺ concentration. The Al accumulation in roots and leaves were significantly different. Al³⁺ concentration above 0.3 mg/L showed toxic to V. natans. TN, TP, IP, Fe/Al-P contents in sediments varied markedly under co-existence of Al and V. natans. Additionally, the relative abundance of sediment microbial community related to N, P cycle was effected. Results concluded that the increasing aquatic Al-concentration inhibits growth and propagation of submerged plants and the ecological restoration effect, and exerts synergistic effect with submerged plants on N, P components in sediments. Such findings were helpful for Al ecological evaluation, and were instructive for the submerged plants restoration in shallow eutrophic lakes with Al input.

Assessment of Air Pollution Tolerance Index (APTI) and Anticipated Performance Index (API) of Roadside Plants for the Development of Greenbelt in Urban Area of Bathinda City, Punjab, India

The aim of the present study is to biomonitor the tolerance level of roadside plant species towards mitigation of air pollution for the development of greenbelt. The leaves of four plant species (Azadirachta indica, Ficus benghalensis, Melia azedarach and Polyalthia longifolia) were collected from 41 sampling sites of Bathinda city during summer and winter seasons. Seasonal variation in APTI and API was determined in selected plants. Highest APTI (13.54) was reported in F. benghalensis during summer and lowest APTI (11.69) in A. indica during winter season. The APTI and API value revealed that F. benghalensis was the best performer, A. indica and M. azedarach were excellent performers and P. longifolia a good performer in greenbelt development to mitigate the air pollution. Pearson's correlation analysis illustrated significant correlation between APTI, ascorbic acid, total chlorophyll, relative water and pH, respectively.

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

Nanoreporter of an Enzymatic Suicide Inactivation Pathway

Enzymatic suicide inactivation, a route of permanent enzyme inhibition, is the mechanism of action for a wide array of pharmaceuticals. Here, we developed the first nanosensor that selectively reports the suicide inactivation pathway of an enzyme. The sensor is based on modulation of the near-infrared fluorescence of an enzyme-bound carbon nanotube. The nanosensor responded selectively to substrate-mediated suicide inactivation of the tyrosinase enzyme via bathochromic shifting of the nanotube emission wavelength. Mechanistic investigations revealed that singlet oxygen generated by the suicide inactivation pathway induced the response. We used the nanosensor to quantify the degree of enzymatic inactivation by measuring response rates to small molecule tyrosinase modulators. This work resulted in a new capability of interrogating a specific route of enzymatic death. Potential applications include drug screening and hit-validation for compounds that elicit or inhibit enzymatic inactivation and single-molecule measurements to assess population heterogeneity in enzyme activity.

Challenging microalgal vitamins for human health

BACKGROUND

Vitamins' deficiency in humans is an important threat worldwide and requires solutions. In the concept of natural biofactory for bioactive compounds production, microalgae represent one of the most promising targets filling many biotechnological applications, and allowing the development of an eco-sustainable production of natural bioactive metabolites. Vitamins are probably one of the cutting edges of microalgal diversity compounds.

MAIN TEXT

Microalgae can usefully provide many of the required vitamins in humans, more than terrestrial plants, for instance. Indeed, vitamins D and K, little present in many plants or fruits, are instead available from microalgae. The same occurs for some vitamins B (B12, B9, B6), while the other vitamins (A, C, D, E) are also provided by microalgae. This large panel of vitamins diversity in microalgal cells represents an exploitable platform in order to use them as natural vitamins' producers for human consumption. This study aims to provide an integrative overview on vitamins content in the microalgal realm, and discuss on the great potential of microalgae as sources of different forms of vitamins to be included as functional ingredients in food or nutraceuticals for the human health. We report on the biological roles of vitamins in microalgae, the current knowledge on their modulation by environmental or biological forcing and on the biological activity of the different vitamins in human metabolism and health protection.

CONCLUSION

Finally, we critically discuss the challenges for promoting microalgae as a relevant source of vitamins, further enhancing the interests of microalgal "biofactory" for biotechnological applications, such as in nutraceuticals or cosmeceuticals.

Nanofomulation of zinc oxide and chitosan zinc sustain oxidative stress and alter secondary metabolite profile in tobacco

Advancement in nanotechnology has improved ways for large-scale production and characterization of nanoparticles of physiologically important metals. The current study explores the impact of Zinc Oxide Nanoparticles (ZnO-NP) and Chitosan-Zinc oxide nano-bioformulation (CH-ZnO) in tissue culture raised callus of Nicotiana benthamiana. Results indicated augmented biomass in CH-ZnO treated callus, while a reduced biomass was observed in ZnO-NP treated callus, at all the concentrations tested. Higher chlorophyll and carotenoid content were recorded in callus treated with 800 ppm CH-ZnO as compared to ZnO-NP treated callus. A higher accumulation of proline was observed in CH-ZnO treated callus when compared to ZnO-NP treatment, which was significantly higher at 50, 200 and 400 ppm CH-ZnO treatment. A maximum reduction in malondialdehyde (MDA) content was recorded at 800 ppm, for both the nano-formulations tested. Likewise, a significant reduction in the H2O2 levels was observed in all the treatments, while the callus treated with 400 ppm ZnO-NP and 800 ppm CH-ZnO recorded the highest reduction. Phenylalanine Ammonia-Lyase (PAL), activity increased significantly in callus treated with 400 ppm concentration for both ZnO-NP and CH-ZnO with respect to control. An increased level of tannin and nicotine were recorded in callus supplemented with 50, 200 and 400 ppm CH-ZnO. Notably, a significant decline of 94 and 52% in tannin content and 25 and 50% in nicotine content was recorded in the callus treated with 800 ppm CH-ZnO and ZnO-NP, respectively. The findings of this study suggest that an optimized dosage of these nano-bioformulations could be utilized to regulate the nicotine content and stress tolerance level.

Biochemical characteristics of urban maple trees

The study, which covers the period between 2014 and 2018, was carried out in the city of Naberezhnye Chelny, Republic of Tatarstan, Russia. The aim of the study was to examine the biochemical response of maple trees growing in the anthropogenic environments. Leaf samples from 600 trees (Acer platanoides L. and Acer negundo L.) were collected at monthly intervals from June through August. Sampling was performed early in the morning (11 a.m.) in the middle of the month. The study offers statistical data on the tannin content, determined via permanganometry; the ascorbic acid concentration, found via titration with 2.6-dichlorophenolindophenol; the ascorbate oxidase activity determined by absorbance at 265 nm; and the polyphenol oxidase activity, found by the spectrophotometric method. Relatively higher ascorbate oxidase activity was detected in August among ash-leaved Acer platanoides L. and Acer negundo L. in areas with strong anthropogenic impact. Due to increased air pollution, maple trees were found to exhibit an increase of polyphenol oxidase activities. The condensed tannin content in Norway maple trees dropped over time: by 1.24 in July (avenue); by 0.94 (buffer area) and 0.76 (avenue) in August. The condensed tannin content in the ash-leaved maple trees also decreased: by 0.69 (buffer area) and 0.22 (avenue) in July; by 0.37 (buffer area) and 0.61(avenue) in August.

Effects of ethylene biosynthesis and signaling on oxidative stress and antioxidant defense system in Nelumbo nucifera G. under cadmium exposure

Water contamination with cadmium (Cd) is a global environmental problem and its remediation becomes urgent. Phytoremediation using ornamental plants has attracted much attention for its advantages of cost-effectiveness and beautification of the environment. Nelumbo nucifera G. is a popular ornamental aquatic macrophyte with fast growth, large biomass, and high capacities for Cd accumulation and removal. However, information about Cd resistance and defense responses in N. nucifera is rather scarce, which restricts its large-scale utilization for phytoremediation. The phytohormone ethylene plays an important role in plant resistance to Cd stress, but the underlying mechanism remains unclear. In this study, we investigated morphophysiological responses of N. nucifera seedlings to Cd stress, and focused on the effects of ethylene on oxidative damage, Cd accumulation, and antioxidant defense system at the metabolic and transcript levels in leaves under Cd stress. Our results showed that Cd exposure led to leaf chlorosis and necrosis, coupled with an increase in contents of hydrogen peroxide, electrolyte leakage, and malondialdehyde, and decrease in chlorophyll content. Exogenous ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) application intensified Cd-induced stress responses and Cd accumulation, and increased ethylene production by inducing ACC synthase (ACS) gene NnACS. Such enhanced ethylene emission inhibited catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities, and modulated ascorbate (AsA) and glutathione (GSH) accumulation through transcriptional regulation of their respective metabolic genes. After ethylene action inhibitor silver thiosulfate (STS) supplementation, Cd-induced oxidative damage was abolished, and Cd content declined but still at a relatively high level. Blocking of ethylene perception by STS inhibited ethylene biosynthesis; enhanced CAT, APX, and GR activities and their transcript levels; increased AsA accumulation via inducing its biosynthetic genes; but reduced GSH content and NnGSH2 expression level. These results suggest that ethylene biosynthesis and signaling play an important role in N. nucifera response to Cd stress, and maintaining appropriate ethylene level and low ethylene sensitivity could improve its Cd tolerance via efficient antioxidant defenses.

Drought-hardening improves drought tolerance in Nicotiana tabacum at physiological, biochemical, and molecular levels

BACKGROUND

Drought stress is the most harmful one among other abiotic stresses with negative impacts on crop growth and development. Drought-hardening is a feasible and widely used method in tobacco seedlings cultivation. It has gained extensive interests due to its role in improving drought tolerance. This research aimed to investigate the role of drought-hardening and to unravel the multiple mechanisms underlying tobacco drought tolerance and adaptation.

RESULTS

This study was designed in which various drought-hardening treatments (CK (no drought-hardening), T1 (drought-hardening for 24 h), T2 (drought-hardening for 48 h), and T3 (drought-hardening for 72 h)) were applied to two tobacco varieties namely HongHuaDaJinYuan (H) and Yun Yan-100 (Y). The findings presented a complete framework of drought-hardening effect at physiological, biochemical, and gene expression levels of the two tobacco varieties under drought stress. The results showed that T2 and T3 significantly reduced the growth of the two varieties under drought stress. Similarly, among the various drought-hardening treatments, T3 improved both the enzymatic (POD, CAT, APX) and non-enzymatic (AsA) defense systems along with the elevated levels of proline and soluble sugar to mitigate the negative effects of oxidative damage and bringing osmoregulation in tobacco plants. Finally, the various drought-hardening treatments (T1, T2, and T3) showed differential regulation of genes expressed in the two varieties, while, particularly T3 drought-hardening treatment-induced drought tolerance via the expression of various stress-responsive genes by triggering the biosynthesis pathways of proline (P5CS1), polyamines (ADC2), ABA-dependent (SnRK2, AREB1), and independent pathways (DREB2B), and antioxidant defense-related genes (CAT, APX1, GR2) in response to drought stress.

CONCLUSIONS

Drought-hardening made significant contributions to drought tolerance and adaptation in two tobacco variety seedlings by reducing its growth and, on the other hand, by activating various defense mechanisms at biochemical and molecular levels. The findings of the study pointed out that drought-hardening is a fruitful strategy for conferring drought tolerance and adaptations in tobacco. It will be served as a useful method in the future to understand the drought tolerance and adaptation mechanisms of other plant species. Drought-hardening improved drought tolerance and adaptation of the two tobacco varieties. T1 indicates drought-hardening for 24 h, T2 indicates drought-hardening for 48 h, T3 indicates drought-hardening for 72 h.

Developmentally controlled changes during Arabidopsis leaf development indicate causes for loss of stress tolerance with age

Leaf senescence is the final stage of leaf development and is induced by the gradual occurrence of age-related changes (ARCs). The process of leaf senescence has been well described, but the cellular events leading to this process are still poorly understood. By analysis of progressively ageing, but not yet senescing, Arabidopsis thaliana rosette leaves, we aimed to better understand processes occurring prior to the onset of senescence. Using gene expression analysis, we found that as leaves mature, genes responding to oxidative stress and genes involved in stress hormone biosynthesis and signalling were up-regulated. A decrease in primary metabolites that provide protection against oxidative stress was a possible explanation for the increased stress signature. The gene expression and metabolomics changes occurred concomitantly to a decrease in drought, salinity, and dark stress tolerance of individual leaves. Importantly, stress-related genes showed elevated expression in the early ageing mutant old5 and decreased expression in the delayed ageing mutant ore9. We propose that the decreased stress tolerance with age results from the occurrence of senescence-inducing ARCs that is integrated into the leaf developmental programme, and that this ensures a timely and certain death.

The antioxidant defense system in Chinese jujube is triggered to cope with phytoplasma invasion

Reactive oxygen species (ROS) in plants increase dramatically under pathogen attack, and the antioxidant defense system is then triggered to protect the plant against the ROS. Jujube witches' broom disease (JWB), caused by phytoplasma, is a destructive disease of Chinese jujube. The results of fluorescence-based measurement revealed that ROS were overproduced within jujube leaves after phytoplasma invasion. Furthermore, analysis based on mRNA and metabolite levels revealed that ascorbic acid (AsA) metabolism was strengthened under phytoplasma stress. The high expression of genes involved in the AsA/glutathione (GSH) cycle and thioredoxin (Trx) synthesis in diseased leaves indicated that GSH and Trx actively respond to phytoplasma infection. Moreover, higher activities of enzymatic antioxidants and the upregulated expression of related genes were confirmed in diseased tissues. Both nonenzymatic and enzymatic antioxidants in the host jujube were strongly stimulated to cope with ROS caused by phytoplasma stress. Compared with that in the susceptible variety, the activities of glutathione S-transferase and peroxidase in the resistant variety at the earlier infection stage were higher, indicating that enzymes might be involved in the resistance to phytoplasma. These results highlight the roles of the antioxidant defense system of the host plant in the tolerance to phytoplasma invasion.

Reactive oxygen species are required for spore wall formation in Physcomitrella patens

A robust spore wall was a key requirement of terrestrialization by early plants. Sporopollenin in spore and pollen grain walls is thought to be polymerized and cross-linked to other macromolecular components partly through oxidative processes involving H2O2. Therefore, we investigated effects of scavengers of reactive oxygen species (ROS) on formation of spore walls in the moss, Physcomitrella patens. Exposure of sporophytes, containing spores in the process of forming walls, to ascorbate, dimethylthiourea or 4-hydroxy-TEMPO prevented normal wall development in a dose, chemical and stage-dependent manner. Mature spores, exposed while developing to a ROS scavenger, burst when mounted in water on a flat slide under a coverslip (a phenomenon we named "augmented osmolysis" since they did not burst in phosphate-buffered saline or in water on a depression slide). Additionally, walls of exposed spores were more susceptible to alkaline hydrolysis than those of control spores and some were characterized by discontinuities in the exine, anomalies in perine spine structure, abnormal intine and aperture and occasionally wall shedding. Our data support involvement of oxidative cross-linking in spore wall development, including sporopollenin polymerization or deposition, as well as a role for ROS in intine/aperture development.

Production of ascorbic acid, total protein, callus and root in vitro of non-heading Chinese cabbage by tissue culture

The objective of the present work was the selection of cultivar, suitable medium and explant type for callus, root production, ascorbic acid, total ascorbic acid, dehydroascorbic and total protein of non-heading Chinese cabbage in two cultivars 'Caixin' and 'Suzhouqing'. We compared 10 types of MS media supplemented with 0.0, 1.0, 2.0 and 3.0 mg/l TDZ; 0.0, 0.25, 0.50 and 1.0 mg/l NAA and 0.0, 5.0, 7.5 and 9.0 mg/l AgNO₃ and 5 kinds of explants as embryo, leaf, root, cotyledon and hypocotyl. Maximum frequency of callus fresh weight was recorded with hypocotyl explant, which were cultured on MS + 2.0 mg/l TDZ + 1.0 mg/l NAA + 9.0 mg/l AgNO₃ in 'Suzhouqing', optimum callus dry weight was obtained on the same media. The highest result for root fresh and dry weight recorded with 'Caixin' with MS + 3.0 mg/l TDZ + 1.0 mg/l NAA + 9.0 mg/l AgNO₃ when we used embryo as explant. The highest ascorbic acid content was found with callus cultured on MS + 1.0 mg/l TDZ + 0.25 mg/l NAA + 5.0 mg/l AgNO₃, when used leaf explant in 'Caixin' or root in 'Suzhouqing', and there were no significant difference between them. While the highest value of total AsA content was registered with callus cultured on MS + 2.0 mg/l TDZ + 0.25 mg/l NAA + 5.0 mg/l AgNO₃ extracted from cotyledon in 'Caixin'. The highest content of DHA was registered with MS + 2.0 mg/l TDZ + 0.25 mg/l NAA + 5.0 mg/l AgNO₃ with cotyledon in 'Caixin'. Also, in 'Caixin' MS + 3.0 mg/l TDZ + 0.25 mg/l NAA + 5.0 mg/l AgNO₃ recorded the highest value of total protein content with embryo explant.

Overexpression of rice glutaredoxin genes LOC_Os02g40500 and LOC_Os01g27140 regulate plant responses to drought stress

Glutaredoxins (Grxs) are small (10-15 kDa) glutathione (GSH) - dependent redox proteins. The role of Grxs are well documented in tolerance to heavy metal stress in prokaryotic and mammalian systems and a few plant genera, but is poorly understood in plants against drought. In the present study, two rice glutaredoxin (Osgrx) genes (LOC_Os02g40500 and LOC_Os01g27140) responsible for tolerance against heavy metal stress have been studied for investigating their role against drought. Each glutaredoxin gene was over-expressed in Arabidopsis thaliana to reveal their role in drought stress. The relative expression of both Osgrx genes was higher in the transgenic lines. Transgenic lines of both Osgrxs showed longer roots, higher seed germination, and survival efficiency during drought stress. The physiological parameters (P_N, g_s, E, WUE, qP, NPQ and ETR), antioxidant enzymes (GRX, GR, GPX, GST, APX, POD, SOD, CAT, DHAR, and MDHAR), antioxidant molecules (ascorbate and GSH) and stress-responsive amino acids (cysteine and proline) levels were additionally increased in transgenic lines of both Osgrxs to provide drought tolerance. The outcomes from this study strongly determined that each Osgrx gene participated in the moderation of drought and might be utilized in biological engineering strategies to overcome drought conditions in different crops.

The Apple microR171i-SCARECROW-LIKE PROTEINS26.1 Module Enhances Drought Stress Tolerance by Integrating Ascorbic Acid Metabolism

Drought stress severely restricts crop yield and quality. Small noncoding RNAs play critical roles in plant growth, development, and stress responses by regulating target gene expression, but their roles in drought stress tolerance in apple (Malus domestica) are poorly understood. Here, we identified various small noncoding RNAs and their targets from the wild apple species Malus sieversii via high-throughput sequencing and degradome analysis. Forty known microRNAs (miRNAs) and eight new small noncoding RNAs were differentially expressed in response to 2 or 4 h of drought stress treatment. We experimentally verified the expression patterns of five selected miRNAs and their targets. We established that one miRNA, mdm-miR171i, specifically targeted and degraded SCARECROW-LIKE PROTEINS26 1 (MsSCL26 1) transcripts. Both knockout of mdm-miR171i and overexpression of MsSCL26 1 improved drought stress tolerance in the cultivated apple line 'GL-3' by regulating the expression of antioxidant enzyme genes, especially that of MONODEHYDROASCORBATE REDUCTASE, which functions in metabolism under drought stress. Transient expression analysis demonstrated that MsSCL26.1 activates MsMDHAR transcription by positively regulating the activity of the P1 region in its promoter. Therefore, the miR171i-SCL26 1 module enhances drought stress tolerance in apple by regulating antioxidant gene expression and ascorbic acid metabolism.

Exogenous proline induces regulation in 2-acetyl-1-pyrroline (2-AP) biosynthesis and quality characters in fragrant rice (Oryza sativa L.)

Proline is one of the precursors of the biosynthesis of 2-acetyl-1-pyrroline (2-AP) which is the key and characteristic volatile component of fragrant rice aroma. In order to study the effects of exogenous proline on 2-AP biosynthesis and other grain quality attributes in fragrant rice, two indica fragrant rice cultivars, "Meixiangzhan-2" and "Xiangyaxiangzhan", and one japonica fragrant rice, "Yunjingyou", were used in present study. At initial heading stage, proline solutions at 0 (CK), 0.10 (Pro1), 0.20 (Pro2) and 0.50 (Pro3) g L^-1 were applied as foliar spray solution to fragrant rice plants. Compared with CK, Pro1, Pro2 and Pro3 treatments significantly increased the grain 2-AP content. The significant up-regulation effects due to proline treatments were observed in the contents of proline, △1-pyrrolidine-5-carboxylic acid (P5C) and △1-pyrroline which involved in 2-AP formation. Exogenous proline application also significantly decreased the grain γ-aminobutyric acid (GABA) content. Furthermore, proline treatments enhanced the activity of proline dehydrogenase (ProDH) as well as transcript level of gene PRODH. On the other hand, the transcript level of gene BADH2 and activity of betaine aldehyde dehydrogenase (BADH) decreased under proline treatments. Proline treatments (Pro2 and Pro3) also increased the grain protein content by 3.57-6.51%. Moreover, 32.03-34.25% lower chalky rice rate and 30.80-48.88% lower chalkiness were recorded in proline treatments (Pro2 and Pro3) for both Meixiangzhan and Xiangyaxiangzhan whilst for Yunjingyou, foliar application of proline had no significant effect on chalky rice rate and chalkiness. There was no remarkable difference observed in grain milled quality (brown rice rate, milled rice rate and head rice rate) and amylose content between CK and proline treatments. In conclusion, exogenous proline enhanced the 2-AP biosynthesis and promoted some grain quality characters of fragrant rice.

ROS Homeostasis in Abiotic Stress Tolerance in Plants

Climate change-induced abiotic stress results in crop yield and production losses. These stresses result in changes at the physiological and molecular level that affect the development and growth of the plant. Reactive oxygen species (ROS) is formed at high levels due to abiotic stress within different organelles, leading to cellular damage. Plants have evolved mechanisms to control the production and scavenging of ROS through enzymatic and non-enzymatic antioxidative processes. However, ROS has a dual function in abiotic stresses where, at high levels, they are toxic to cells while the same molecule can function as a signal transducer that activates a local and systemic plant defense response against stress. The effects, perception, signaling, and activation of ROS and their antioxidative responses are elaborated in this review. This review aims to provide a purview of processes involved in ROS homeostasis in plants and to identify genes that are triggered in response to abiotic-induced oxidative stress. This review articulates the importance of these genes and pathways in understanding the mechanism of resistance in plants and the importance of this information in breeding and genetically developing crops for resistance against abiotic stress in plants.