Influence of natural and synthetic vitamin C (ascorbic acid) on primary and secondary metabolites and associated metabolism in quinoa (Chenopodium quinoa Willd.) plants under water deficit regimes

Genetics aspect of vitamin C (Ascorbic Acid) biosynthesis and signaling pathways in fruits and vegetables crops

Vitamin C, also known as ascorbic acid, is an essential nutrient that plays a critical role in many physiological processes in plants and animals. In humans, vitamin C is an antioxidant, reducing agent, and cofactor in diverse chemical processes. The established role of vitamin C as an antioxidant in plants is well recognized. It neutralizes reactive oxygen species (ROS) that can cause damage to cells. Also, it plays an important role in recycling other antioxidants, such as vitamin E, which helps maintain the overall balance of the plant's antioxidant system. However, unlike plants, humans cannot synthesize ascorbic acid or vitamin C in their bodies due to the absence of an enzyme called gulonolactone oxidase. This is why humans need to obtain vitamin C through their diet. Different fruits and vegetables contain varying levels of vitamin C. The biosynthesis of vitamin C in plants occurs primarily in the chloroplasts and the endoplasmic reticulum (ER). The biosynthesis of vitamin C is a complex process regulated by various factors such as light, temperature, and plant hormones. Recent research has identified several key genes that regulate vitamin C biosynthesis, including the GLDH and GLDH genes. The expression of these genes is known to be regulated by various factors such as light, temperature, and plant hormones. Recent studies highlight vitamin C's crucial role in regulating plant stress response pathways, encompassing drought, high salinity, and oxidative stress. The key enzymes in vitamin C biosynthesis are L-galactose dehydrogenase (GLDH) and L-galactono-1, 4-lactone dehydrogenase (GLDH). Genetic studies reveal key genes like GLDH and GLDH in Vitamin C biosynthesis, offering potential for crop improvement. Genetic variations influence nutritional content through their impact on vitamin C levels. Investigating the roles of genes in stress responses provides insights for developing resilient techniques in crop growth. Some fruits and vegetables, such as oranges, lemons, and grapefruits, along with strawberries and kiwi, are rich in vitamin C. Guava. Papaya provides a boost of vitamin C and dietary fiber. At the same time, red and yellow bell peppers, broccoli, pineapple, mangoes, and kale are additional sources of this essential nutrient, promoting overall health. In this review, we will discuss a brief history of Vitamin C and its signaling and biosynthesis pathway and summarize the regulation of its content in various fruits and vegetables.

Multi-omics analysis provides insights intro lysine accumulation in quinoa (Chenopodium quinoa Willd.) sprouts

Lysine, the first limiting essential amino acid, the deficiency of which seriously affects the health of human and animals. In this study, quinoa germination significantly increased the nutrients, especially lysine content. To better understanding the underlying molecular mechanism of lysine biosynthesis, isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics, RNA-sequencing (RNA-Seq) technology and liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) platform-based phytohormones analyses were conducted. Through proteome analyses, a total of 11,406 differentially expressed proteins were identified, which were mainly related to secondary metabolites. The lysine-rich storage globulins and endogenous phytohormones probably contributed the increased lysine content in quinoa during germination. Furthermore, aspartic acid semialdehyde dehydrogenase is essential for lysine synthesis in addition to aspartate kinase and dihydropyridine dicarboxylic acid synthase. Protein-protein interaction analysis indicated lysine biosynthesis is associated with "amino metabolism" and "starch and sucrose metabolism". Above all, our study screens the candidate genes participated in lysine accumulation and explores the factors affected lysine biosynthesis by multi-omics analysis. These information not only paves a foundation for breeding lysine-rich quinoa sprouts but also provides valuable multi-omics resource to explore the characteristic of nutrients during quinoa germination.

Physiological and biochemical roles of ascorbic acid on mitigation of abiotic stresses in plants

Under conditions of abiotic stress several physiological and biochemical processes in plants can be modified. The production of reactive oxygen species (ROS) is toxic at high concentrations and promotes RNA, DNA and plant cell membrane degradation. Plants have enzymatic and non-enzymatic adaptation mechanisms to act against ROS detoxification. Ascorbic acid (AsA) is the non-enzymatic compound essential for several biological functions, which acts in the elimination and balance of ROS production and with the potential to promote several physiological functions in plants, such as the photosynthetic process. For plant development, AsA plays an important role in cell division, osmotic adjustment, hormone biosynthesis, and as an enzymatic cofactor. In this review, the redox reactions, biosynthetic pathways, and the physiological and biochemical functions of AsA against abiotic stress in plants are discussed. The concentration of AsA in plants can vary between species and depend on the biosynthetic pathways d-mannose/l-galactose, d-galacturonate, euglenids, and d-glucuronate. Although the endogenous levels of AsA in plants are used in large amounts in cell metabolism, the exogenous application of AsA further increases these endogenous levels to promote the antioxidant system and ameliorate the effects produced by abiotic stress. Foliar application of AsA promotes antioxidant metabolism in plants subjected to climate change conditions, also allowing the production of foods with higher nutritional quality and food safety, given the fact that AsA is biologically essential in the human diet.

Research Progress of Quinoa Seeds (Chenopodium quinoa Wild.): Nutritional Components, Technological Treatment, and Application

Quinoa (Chenopodium quinoa Wild.) is a pseudo-grain that belongs to the amaranth family and has gained attention due to its exceptional nutritional properties. Compared to other grains, quinoa has a higher protein content, a more balanced amino acid profile, unique starch features, higher levels of dietary fiber, and a variety of phytochemicals. In this review, the physicochemical and functional properties of the major nutritional components in quinoa are summarized and compared to those of other grains. Our review also highlights the technological approaches used to improve the quality of quinoa-based products. The challenges of formulating quinoa into food products are addressed, and strategies for overcoming these challenges through technological innovation are discussed. This review also provides examples of common applications of quinoa seeds. Overall, the review underscores the potential benefits of incorporating quinoa into the diet and the importance of developing innovative approaches to enhance the nutritional quality and functionality of quinoa-based products.

GA signaling protein LsRGL1 interacts with the abscisic acid signaling-related gene LsWRKY70 to affect the bolting of leaf lettuce

A variety of endogenous hormone signals, developmental cues, and environmental stressors can trigger and promote leaf lettuce bolting. One such factor is gibberellin (GA), which has been linked to bolting. However, the signaling pathways and the mechanisms that regulate the process have not been discussed in full detail. To clarify the potential role of GAs in leaf lettuce, significant enrichment of GA pathway genes was found by RNA-seq, among which the LsRGL1 gene was considered significant. Upon overexpression of LsRGL1, a noticeable inhibition of leaf lettuce bolting was observed, whereas its knockdown by RNA interference led to an increase in bolting. In situ hybridization analysis indicated a significant accumulation of LsRGL1 in the stem tip cells of overexpressing plants. Leaf lettuce plants stably expressing LsRGL1 were examined concerning differentially expressed genes through RNA-seq analysis, and the data indicated enhanced enrichment of these genes in the 'plant hormone signal transduction' and 'phenylpropanoid biosynthesis' pathways. Additionally, significant changes in LsWRKY70 gene expression were identified in COG (Clusters of Orthologous Groups) functional classification. The results of yeast one-hybrid, β-glucuronidase (GUS), and biolayer interferometry (BLI) experiments showed that LsRGL1 proteins directly bind to the LsWRKY70 promoter. Silencing LsWRKY70 by virus-induced gene silencing (VIGS) can delay bolting, regulate the expression of endogenous hormones, abscisic acid (ABA)-linked genes, and flowering genes, and improve the nutritional quality of leaf lettuce. These results strongly associate the positive regulation of bolting with LsWRKY70 by identifying its vital functions in the GA-mediated signaling pathway. The data obtained in this research are invaluable for further experiments concerning the development and growth of leaf lettuce.

Differential Effect of Heat Stress on Drought and Salt Tolerance Potential of Quinoa Genotypes: A Physiological and Biochemical Investigation

Soil salinity, drought, and increasing temperatures are serious environmental issues that drastically reduce crop productivity worldwide. Quinoa (Chenopodium quinoa Willd) is an important crop for food security under the changing climate. This study examined the physio-biochemical responses, plant growth, and grain yield of four quinoa genotypes (A7, Titicaca, Vikinga, and Puno) grown in pots containing normal (non-saline) or salt-affected soil exposed to drought and elevated-temperature treatments. Combinations of drought, salinity, and high-temperature stress decreased plant growth and yield more than the individual stresses. The combined drought, salinity, and heat stress treatment decreased the shoot biomass of A7, Puno, Titicaca, and Vikinga by 27, 36, 41, and 50%, respectively, compared to that of control plants. Similar trends were observed for grain yield, chlorophyll contents, and stomatal conductance. The combined application of these three stresses increased Na concentrations but decreased K concentrations in roots and shoots relative to control. Moreover, in the combined salinity, drought, and high-temperature treatment, A7, Puno, Titicaca, and Vikinga had 7.3-, 6.9-, 8-, and 12.6-fold higher hydrogen peroxide contents than control plants. All four quinoa genotypes increased antioxidant enzyme activities (CAT, SOD, and POD) to overcome oxidative stress. Despite A7 producing the highest biomass under stress, it did not translate into increased grain production. We conclude that Puno and Titicaca are more tolerant than Vikinga for cultivation in salt-affected soils prone to drought and heat stress.

Supportive effect of naringenin on NaCl-induced toxicity in Carthamus tinctorius seedlings

In the present study, we used exogenous naringenin (0.5 mM) pretreatment before the stress (25 mM NaCl) on the growth and tolerance of safflower seedlings under non-salinity conditions and salinity conditions. Our results showed that salinity treatment significantly declined the biomass, leaf relative water content, chlorophyll content, K⁺ content, and K⁺/Na⁺ ratio by 28%, 28%, 12%, 36%, and 56%, respectively, as compared to untreated control. The results obtained in the present study showed the beneficial effects of the pretreatment of naringenin in safflower seedlings under non-salinity conditions concerning increasing plant biomass, total phenolic compound, radical scavenging activity (RSA), soluble sugar content, proline, glutathione, enzymatic antioxidants, and K⁺ content. Nevertheless, naringenin pretreated plants showed a clear increment in the values of biomass, RSA, total phenolic compound, and catalase enzyme activity parameters under salinity stress. Salinity stress caused ionic phytotoxicity and oxidative stress by enhancing Na⁺ content, H₂O₂ accumulation, malondialdehyde (MDA), and antioxidants. However, naringenin alleviated salt-induced oxidative stress by decreasing H₂O₂ and MDA content in the leaves and improving the catalase activity in treated plants. Generally, it could be concluded pretreatment of naringenin before stress could partly diminish NaCl-caused oxidative stress in safflower seedlings, probably due to improvement in enzymatic and non-enzymatic antioxidants and reduced cell membrane damage.

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

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

The Role of Plant Growth Regulators in Modulating Root Architecture and Tolerance to High-Nitrate Stress in Tomato

Plant growth regulators are known to exert strong influences on plant performance under abiotic stress, including exposure to high nitrate, as occurs commonly in intensive vegetable production. However, direct comparative evaluations of growth regulators under otherwise identical conditions in major crop species are scarce. In this study, tomato (Solanum lycopersicum L.) was used as a model crop, and the roles of four common exogenously applied plant growth regulators (MT, melatonin; SA, salicylic acid; HA, humic acid; SNP, sodium nitroprusside) in regulating crop growth were studied under high-nitrate stress. We provide a particular focus on root system architecture and root physiological responses. Our data show that all four growth regulators improve tomato tolerance under high nitrate, but that this occurs to differing extents and via differing mechanisms. Optimal concentrations of MT, SA, HA, and SNP were 50 μmol L^-1, 25 μmol L^-1, 25 mg L^-1, and 50 μmol L^-1, respectively. MT and SNP produced the strongest effects. MT enhanced root growth while SNP enhanced above-ground growth. Growth of coarse and thin lateral roots was significantly improved. Furthermore, an enhancement of root vitality and metabolism, improved integrity of root cell membranes, and an increase in antioxidant enzyme activities were found, but regulatory mechanisms were different for each growth regulator. Our results show that in particular the application of MT and SNP can improve growth of tomato in intensive vegetable production under high-nitrate stress and that root growth stimulation is of special importance in procuring these beneficial effects.

Exogenous ascorbic acid application alleviates cadmium toxicity in seedlings of two wheat (Triticum aestivum L.) varieties by reducing cadmium uptake and enhancing antioxidative capacity

The aggravation of soil cadmium (Cd) pollution is a serious threat to human food health and safety. To reduce Cd uptake and alleviate Cd toxicity in staple food of wheat, a completely random experiment was performed to investigate the effect of exogenous ascorbic acid (AsA) on Cd toxicity in two wheat varieties (L979 and H27). In this study, the treatments with combinations of Cd (0, 5, and 10 µmol L^-1) and AsA (0, 50, and 200 µmol L^-1) were applied in a hydroponic system. Toxicity induced by Cd inhibited biomass accumulation; decreased wheat growth, photosynthesis, and chlorophyll content; increased lipid peroxidation; and reduced activity of superoxide dismutase (SOD), but stimulated catalase (CAT) and peroxidase (POD). The addition of AsA significantly improved the growth status by increasing the wheat biomass, chlorophyll content, photosynthetic rate, protein concentrations, and antioxidant enzyme activity. Besides, AsA significantly decreased Cd concentration of shoot and root by 14.1-53.9% and 20.8-59.5% in L979 and 23.7-58.8% and 22.1-58.1% in H27 under Cd5, and 23.7-53.6% and 16.6-57.1% in L979 and 21.5-51.6% and 15.3-54.0% in H27 under Cd10, respectively. Malondialdehyde (MDA) accumulation was decreased remarkably with the addition of AsA by 31.2-32.9% in L979 and 27.1-45.2% in H27 under Cd10, respectively. Overall, exogenous application of AsA alleviated the Cd toxicity in wheat plants by improving the wheat growth, soluble protein content, photosynthesis, and antioxidant defense systems, and decreasing MDA accumulation.

Spatial variations in the biochemical potential of okra [Abelmoschus esculentus L. (Moench)] leaf and fruit under field conditions

Okra (Abelmoschus esculentus L. (Moench) plays a significant role in humans nutrition because its fresh leaves, stems, flowers, pods and seeds, are used for multiple purposes. The present study attempted to determine the spatial variations in biochemical attributes of osmoprotectants and the oxidative defense system of okra plants. Samples of soil and okra plants (leaves and fruits) were collected from three different locations: Faisalabad region-1 (7 JB-I), Faisalabad region-2 (7 JB-II) and Pindi Bhattian. Chlorophyll contents, glycine betaine (GB), ascorbic acid (AsA), total phenolics, hydrogen peroxide (H₂O₂), proline, and malondialdehyde (MDA) contents were analyzed in the leaves and fruits of okra plants. Soil analyses showed that pH, electrical conductivity (EC), phosphorus (P), potassium (K), iron (Fe), and saturation of soil were higher in Faisalabad region 2, while organic matter, sand, Zn, and Cu were higher in the Pindi Bhattian region. The results from okra leaves showed that Pindi Bhattian had higher chlorophyll a, GB and H₂O₂ contents, while Faisalabad region 1 had a higher ratio of chlorophyll a/b compared to the other regions. However, Faisalabad regions 2 and 1 had higher leaf phenolic contents, Faisalabad regions 1 and 2 showed higher leaf proline contents, and Faisalabad region 2 possessed higher AsA and MDA contents. Analyses of okra fruits showed that Faisalabad region 2 had higher chlorophyll a and total chlorophyll contents, while Faisalabad region 1 had higher chlorophyll b contents. Faisalabad region 2 and Pindi Bhattian had higher ratios of chlorophyll a/b, and Faisalabad region 1 showed higher phenolic, AsA, H₂O₂, and MDA contents of okra fruit, whereas the Faisalabad regions exhibited higher proline and GB contents than the Pindi Bhattian region. Overall, okra leaves and fruits showed better responses in the Faisalabad regions, and these results may be used to screen for okra cultivars with better tolerance under different environmental conditions.

R, Choudhary AK, Salam MD, Sahoo MR, Bhutia TL, Devi SH, Thounaojam AS, Behera C, M. N. H, Kumar A, Dasgupta M, Devi YP, Singh D, Bhagowati S, Devi CP, Singh HR, Khaba CI. Role of biostimulants in mitigating the effects of climate change on crop performance

Climate change is a critical yield-limiting factor that has threatened the entire global crop production system in the present scenario. The use of biostimulants in agriculture has shown tremendous potential in combating climate change-induced stresses such as drought, salinity, temperature stress, etc. Biostimulants are organic compounds, microbes, or amalgamation of both that could regulate plant growth behavior through molecular alteration and physiological, biochemical, and anatomical modulations. Their nature is diverse due to the varying composition of bioactive compounds, and they function through various modes of action. To generate a successful biostimulatory action on crops under different parameters, a multi-omics approach would be beneficial to identify or predict its outcome comprehensively. The 'omics' approach has greatly helped us to understand the mode of action of biostimulants on plants at cellular levels. Biostimulants acting as a messenger in signal transduction resembling phytohormones and other chemical compounds and their cross-talk in various abiotic stresses help us design future crop management under changing climate, thus, sustaining food security with finite natural resources. This review article elucidates the strategic potential and prospects of biostimulants in mitigating the adverse impacts of harsh environmental conditions on plants.

Leaf extract of neem (Azadirachta indica) alleviates adverse effects of drought in quinoa (Chenopodium quinoa Willd.) plants through alterations in biochemical attributes and antioxidants

The influence of varying concentrations (0, 1, 3, 4, 5, 6, 8, and 10 % v/v) of neem (Azadirachta indica) leaf extract on drought stressed (40 % field capacity) quinoa (Chenopodium quinoa Willd.) plants was assessed. During the current study two cultivars of quinoa (V7 and V9) were used. This study revealed that water stress adversely affects the fresh and dry weight of shoots and roots as well as chlorophyll pigments (a and b) of both quinoa cultivars. In contrast, drought stress enhanced glycinebetaine (GB), free proline, phenolic content, hydrogen peroxide (H₂O₂), activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzymes, and relative membrane permeability (RMP). However, application of neem leaf extract improved the accumulation of key osmoprotectants like proline, GB and activities of enzymatic antioxidants. Our findings showed 5 % neem leaf extract is an effective treatment in counteracting the oxidative damage caused by water stress, thereby improving overall plant growth. Of both cultivars of quinoa, the response of cv. V9 to stress as well as foliar applied neem was relatively more promising.

Hydrogen sulfide mediates defense response in safflower by regulating secondary metabolism, oxidative defense, and elemental uptake under drought

Hydrogen sulfide (H₂ S) is a newly recognized molecule mediating plant defense responses under drought. The role of exogenous H₂ S in regulating plant responses under drought has been reported in a few plant species including spinach, wheat, Arabidopsis, soybean, and citrus plants. However, no report is available on the outcome of exogenous H₂ S on drought response in safflower plants. Therefore, the present study was planned to get insight into H₂ S-mediated regulation of growth, secondary metabolism, oxidative defense, and uptake of minerals in two safflower cultivars (Safflower-16427 and Safflower-16493). Plants were exposed to two NaHS (0.5 and 1.0 mM) and two drought levels (70 and 50% field capacity [FC]). We found a notable depression in growth, yield, chlorophyll, and potassium (K⁺ ) uptake under drought. The decline was more significant in plants facing 50% FC. The oxidative injury in plants was higher under severe drought and led to the decline in chlorophyll, plant biomass, and yield production. Drought induced a noticeable accretion in the accumulation of total soluble sugars, proline, ascorbic acid, anthocyanins, and secondary metabolites that protect plants against oxidative damages caused by drought. The activities of antioxidant enzymes increased substantially in safflower cultivars under drought. Besides, plants pretreated with NaHS (0.5 mM) subsided the oxidative damage by increasing the accumulation of secondary metabolites and strengthening the antioxidant capacity under drought. Further, drought plants suffered significant disturbances in ions homeostasis that was circumvented by exogenous H₂ S. The interactive effect of drought and H₂ S did not display a significant difference between the cultivars.

Impact of exogenously applied trehalose on leaf biochemistry, achene yield and oil composition of sunflower under drought stress

This study was carried out to assess the influence of trehalose, a non-reducing disaccharide involved in improving plant stress tolerance, on two cultivars (Hysun 33 and FH 598) of sunflower (Helianthus annuus L.) grown under control and drought stress conditions. At pre-flowering stage, varying concentrations (10, 20 and 30 mM) of trehalose were applied to the foliage. Drought stress significantly suppressed the plant growth, total soluble proteins, chlorophyll, achene yield per plant, oil percentage, organic contents, as well as oil palmitic and linoleic acids in both sunflower cultivars. External application of trehalose significantly reduced RMP (relative membrane permeability), and the accumulation of H₂ O₂ (hydrogen peroxide), while a considerable improvement was recorded in shoot fresh and shoot and root dry weights, total soluble proteins, glycinebetaine, AsA (ascorbic acid), total phenolics, achene yield per plant, oil contents, inorganic and organic contents, and the activities of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) enzymes under water-limited regimes. The cultivar Hysun 33 was superior to the other cultivar in plant growth, RMP, glycinebetaine, proline, achene yield per plant, oil contents, and palmitic and linoleic acids. Overall, foliar-applied trehalose improved plant growth, oxidative defense system, yield and oil composition of sunflower under drought stress conditions.

Exogenous Application of Zinc to Mitigate the Salt Stress in Vigna radiata (L.) Wilczek-Evaluation of Physiological and Biochemical Processes

Salt stress adversely affects the growth and productivity of crops. However, reports suggest that the application of various micronutrients could help the plant to cope with this stress. Hence, the objective of the study was to examine the effect of exogenous application of Zinc (Zn) on salt tolerance in Vigna radiata (L.) Wilczek (mungbean). Mungbean is considered to be an economically important crop and possess a strategic position in Southeast Asian countries for sustainable crop production. It is rich in quality proteins, minerals and vitamins. Three weeks old grown seedlings were subjected to NaCl (150 mM and 200 mM) alone or with Zn (250 µM). After 21 days of treatment, plants were harvested for investigating morphological, physiological and biochemical changes. We found that the Zn application mitigates the negative effect upon plant growth to a variable extent. This may be attributed to the increased shoot and root length, improved chlorophyll and carotenoid contents, enhanced total soluble sugar (TSS), total soluble protein (TSP) and proline accumulation, decreased H2O2 content and increased enzymatic antioxidant activities. Zn's application improved the performance of the enzymes such as phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) of the secondary metabolism, which resulted in the improvement of total phenol and flavonoids. The antioxidant activities such as 1,1diphenyl 2-picryl hydrazine (DPPH) and ferrous reducing antioxidant power assay (FRAP) of the plants also showed improved results in their salt only treatments. Furthermore, hydrogen peroxide (H2O2) and superoxide radical (SOD) scavenging activity were also improved upon the application of 250 µM zinc. Thus, Zn application in low doses offers promising potential for recovering plants suffering from salinity stress. In conclusion, we assume that zinc application improved salt tolerance in mungbean through the improvement of various physiological and photochemical processes which could prove to be useful in nutrient mediated management for crop improvement.

Antioxidant Enzymatic Activities and Growth Response of Quinoa (Chenopodium quinoa Willd) to Exogenous Selenium Application

Selenium is a trace element essential to many organisms, including higher plants. At low concentrations, it enhances growth and development; however, it is toxic at high concentrations. The development of crops with proper levels of selenium will be worth for both nutrition and Se-based therapeutics. This study aimed to investigate the morphological, physiological, and biochemical responses of the quinoa plant to 0, 2.5, 5, 10, and 20 mg/L of Na2SeO3·5H2O. Selenium at low concentrations (2.5 and 5 mg/L), quinoa plant showed a significant increase of growth parameters, relative water content, photosynthetic pigments, proline, total soluble sugars, and antioxidant enzymes activities as (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD, ascorbate peroxidase (APX), and glutathione reductase (GR)), and contents of malondialdehyde (MDA) and H2O2 were reduced. However, high concentrations (10 and 20) mg/L caused a decrease in plant growth parameters, relative water content, and photosynthetic pigments. In contrast, excess selenium increased the oxidative stress monitored by hydrogen peroxide and lipid peroxidation levels. The enzymatic antioxidant system responded to the selenium supply significantly increased. Osmolytes compounds, such as total sugars and proline, increased in selenium-treated plants. The increase in these osmolytes compounds may show a defense mechanism for the osmotic readjustment of quinoa plants to mitigate the toxicity caused by selenium. This study shows the morphological and physiological responses that must be considered for success in the sustainable cultivation of quinoa plants in environments containing excess selenium.

Foliar application of ascorbic acid enhances salinity stress tolerance in barley (Hordeum vulgare L.) through modulation of morpho-physio-biochemical attributes, ions uptake, osmo-protectants and stress response genes expression

Barley (Hordeum vulgare L.) is a major cereal grain and is known as a halophyte (a halophyte is a salt-tolerant plant that grows in soil or waters of high salinity). We therefore conducted a pot experiment to explore plant growth and biomass, photosynthetic pigments, gas exchange attributes, stomatal properties, oxidative stress and antioxidant response and their associated gene expression and absorption of ions in H. Vulgare. The soil used for this analysis was artificially spiked at different salinity concentrations (0, 50, 100 and 150 mM) and different levels of ascorbic acid (AsA) were supplied to plants (0, 30 and 60 mM) shortly after germination of the seed. The results of the present study showed that plant growth and biomass, photosynthetic pigments, gas exchange parameters, stomatal properties and ion uptake were significantly (p < 0.05) reduced by salinity stress, whereas oxidative stress was induced in plants by generating the concentration of reactive oxygen species (ROS) in plant cells/tissues compared to plants grown in the control treatment. Initially, the activity of antioxidant enzymes and relative gene expression increased to a saline level of 100 mM, and then decreased significantly (P < 0.05) by increasing the saline level (150 mM) in the soil compared to plants grown at 0 mM of salinity. We also elucidated that negative impact of salt stress in H. vulgare plants can overcome by the exogenous application of AsA, which not only increased morpho-physiological traits but decreased oxidative stress in the plants by increasing activities of enzymatic antioxidants. We have also explained the negative effect of salt stress on H. vulgare can decrease by exogenous application of AsA, which not only improved morpho-physiological characteristics, ions accumulation in the roots and shoots of the plants, but decreased oxidative stress in plants by increasing antioxidant compounds (enzymatic and non-enzymatic). Taken together, recognizing AsA's role in nutrient uptake introduces new possibilities for agricultural use of this compound and provides a valuable basis for improving plant tolerance and adaptability to potential salinity stress adjustment.

Abiotic Stress in Crop Species: Improving Tolerance by Applying Plant Metabolites

Reductions in crop yields brought about by abiotic stress are expected to increase as climate change, and other factors, generate harsher environmental conditions in regions traditionally used for cultivation. Although breeding and genetically modified and edited organisms have generated many varieties with greater abiotic stress tolerance, their practical use depends on lengthy processes, such as biological cycles and legal aspects. On the other hand, a non-genetic approach to improve crop yield in stress conditions involves the exogenous application of natural compounds, including plant metabolites. In this review, we examine the recent literature related to the application of different natural primary (proline, l-tryptophan, glutathione, and citric acid) and secondary (polyols, ascorbic acid, lipoic acid, glycine betaine, α-tocopherol, and melatonin) plant metabolites in improving tolerance to abiotic stress. We focus on drought, saline, heavy metal, and temperature as environmental parameters that are forecast to become more extreme or frequent as the climate continues to alter. The benefits of such applications are often evaluated by measuring their effects on metabolic, biochemical, and morphological parameters in a variety of crop plants, which usually result in improved yields when applied in greenhouse conditions or in the field. As this strategy has proven to be an effective way to raise plant tolerance to abiotic stress, we also discuss the prospect of its widespread implementation in the short term.

Menadione sodium bisulfite neutralizes chromium phytotoxic effects in okra by regulating cytosolutes, lipid peroxidation, antioxidant system and metal uptake

Chromium (Cr) is a major abiotic stress for plant species that significantly impacted plant development and impeded agricultural production. Menadione sodium bisulfite (MSB) has recently manifested a remarkable role in modulating plant defense responses. In the present experiment, Cr caused a significant decrease in growth, relative water contents, and chlorophyll in okra cultivars (Shabnam 786 and Arka Anamika). Cr produced an increase in proline, total soluble proteins, total free amino acids, phenolics, flavonoids, ascorbic acid, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and Cr accumulation. Besides, activities of antioxidant enzymes were also higher in Cr-stressed plants. MSB application (50, 100, 150, and 200 µM) profoundly impacted growth and important physio-biochemical characteristics in okra under Cr stress. Better growth in MSB treated plants was associated with lower oxidative damage and better oxidative defense system reflected in the form of higher antioxidant enzyme activities alongside the concentrations of non-enzymatic antioxidant compounds. In this background, cv. Shabnam-786 exhibited greater Cr tolerance over Arka Anamika. The degree of oxidative damage measured in the form of H₂O₂ and MDA was greater in cv. Arka Anamika. Lower MSB levels (50 and 100 µM) circumvented inhibitory Cr effects in okra, while higher doses proved lethal for plant growth and development.

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.

Ascorbic acid alleviation of manganese-induced toxicity in Vallisneria natans (Lour.) Hara

We investigated the growth and physiological responses of the submerged aquatic plant species Vallisneria natans (Lour.) Hara to 80 mg L^-1 manganese (Mn) with different doses of ascorbic acid (AsA 0, 5, 10, 20, 50, 100, 200 mg L^-1) after 21 days of treatment. Mn stress significantly reduced the final leaf number and superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities of V. natans, while increased the malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and proline contents, and peroxidase (POD) activity, with no significant differences in plant relative growth rate (RGR) and photosynthetic pigment contents. With increasing doses of AsA supplementation (≤ 50 mg L^-1), the MDA content gradually decreased, while the proline, soluble protein, and photosynthetic pigment contents, antioxidase (except POD) activities, and RGR of V. natans increased. AsA levels ≥ 100 mg L^-1 exacerbated Mn toxicity in V. natans by significantly reducing the antioxidase activities and photosynthetic pigment contents and even triggering plant lethal effects. These results suggest that the Mn stress induced in this investigation could bring about oxidative stress and influence the growth of V. natans. Moreover, the optimal AsA dose that can alleviate Mn-induced oxidative stress was 41.37-50.25 mg L^-1 according to the regression analysis based on plant growth and enzymatic responses.

Sulfur-enriched leonardite and humic acid soil amendments enhance tolerance to drought and phosphorus deficiency stress in maize (Zea mays L.)

Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha⁻¹), P deficiency (phosphorus stress (PS): 62.5 kg P ha⁻¹), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha⁻¹). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha⁻¹ and (iii) 1250 kg S + 37.5 kg humic acid ha⁻¹) tested on stress treatments. Drought and P deficiency reduced plant biomass, grain yield, chlorophyll content, F_v/F_m, RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H₂O₂ in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils.

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.

Physicochemical and functional properties of isolated starch and their correlation with flour from the Andean Peruvian quinoa varieties

Quinoa has been recognized as a complete food due to its balanced nutritional composition. Quinoa flour is used as an ingredient to improve the nutritional and functional characteristics of cereal-based foods. The physicochemical and functional (thermal and pasting) properties of flours and isolated starches of three Andean Peruvian quinoa varieties (Blanca de Hualhuas, BH; Rosada de Huancayo, RHY and Pasankalla, PK) were studied and the correlation among them properties were evaluated in order to explore their possible uses as a food ingredient. Proximal chemical composition of flour and isolated starches from quinoa varieties showed differences. Isolated starches from quinoa varieties showed a XRD Type A crystallinity patterns with polygonal shapes, small size, higher crystallinity degree and lower amylose content (<15%). The thermal (gelatinization temperatures and enthalpies) and pasting (temperature and time of gelatinization and viscosities) properties of flours and isolated starches showed differences and the principal component analysis demonstrated that those properties are significantly correlated to the starch and fat content. Based on the differences found among physicochemical and functional properties, isolated starch and flour of BH, RHY and PK quinoa varieties have potential as food ingredient for several cereal-based products.

C4 photosynthetic enzymes play a key role in wheat spike bracts primary carbon metabolism response under water deficit

C4 photosynthetic enzymes are present in C3 plants and participate in non-photosynthetic metabolism. Wheat spike bracts had a higher drought tolerance, photosynthesis and senesced later compared to the flag leaves under water deficit. This research was conducted to investigate the different response of primary carbon metabolism induced by C4 photosynthetic enzymes in wheat flag leaves and spike bracts including glumes and lemmas under water deficit. The activities of C4 photosynthetic enzymes and Ribulose bisphosphate carboxylase oxygenase (Rubisco), the expression of related genes and primary carbon metabolism contents were demonstrated in wheat flag leaves and spike bracts exposed to water deficit. Results showed that drought stress strongly inhibited wheat photosynthetic metabolism by decreasing Rubisco activity in flag leaves. The activities of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), phosphate dikinase (PPDK) and NADP- malic dehydrogenase (NADP-MDH) increased in wheat spike bracts under water deficit. Transcript levels of C4 photosynthetic genes in wheat spike bracts were higher under water deficit than that of control. Furthermore, the results indicated that drought stress induced changes in the contents of primary carbon metabolism including malate, oxaloacetic acid (OAA), citric, fumaric acid were organ-specific. In conclusion, the functions of C4 photosynthetic enzymes appear to be important for wheat spike bracts primary carbon metabolism and defence response under drought stress.

Exogenous application of ascorbic acid mitigates cadmium toxicity and uptake in Maize (Zea mays L.)

Cadmium (Cd) contamination in agricultural soils is a prevalent environmental issue and poses potential threats to food security. Foliar ascorbic acid might prove a potent tool to alleviate toxicity of Cd toxicity in maize. An experiment was conducted with objectives to study exogenous ascorbic acid-modulated improvements in physiochemical attributes of maize under Cd toxicity. The experiment was conducted under completely randomized design. Treatments were comprised of varying concentrations of foliar ascorbic acid viz. 0.0, 0.1, 0.3, and 0.5 mM of AsA. Toxicity of Cd decreased the maize growth, increased lipid peroxidation, disturbed protein metabolism, and reduced the antioxidant defense capabilities compared with the control. However, foliar AsA significantly improved maize growth and development, photosynthetic capabilities, and protein concentrations in Cd-stressed maize plants. Meanwhile, the malondialdehyde contents and hydrogen peroxide accumulation levels in Cd-stressed maize plants decreased remarkably with increasing AsA concentrations. Furthermore, the combined treatments conspicuously boosted activities of superoxide dismutase, peroxidase, catalase, and glutathione reductase under the Cd stress alone. In addition, the application of AsA reduced the Cd uptake by 10.3-12.3% in grains. Conclusively, foliar ascorbic acid alleviated the negative effects of Cd stress in maize and improved photosynthetic processes, osmolytes, and antioxidant defense systems.

Differential response of quinoa genotypes to drought and foliage-applied H2O2 in relation to oxidative damage, osmotic adjustment and antioxidant capacity

Quinoa (Chenopodium quinoa Willd.), a highly nutritious grain crop, is resistant to abiotic stresses (drought, salinity, and cold) and offers an alternate crop to endure harsh environmental conditions under the face of climate change. Naturally, quinoa genome displays a wide degree of variabilities in drought tolerance strategies. Therefore, the present study was designed to investigate drought tolerance variations and stress tolerance enhancement in four quinoa genotypes (Pichaman, Colorado-407D, IESP and 2-Want) thorough foliage-applied H₂O₂ with the purpose of identifying suitable genotype for water limited environments. The plants were exposed to two watering regimes (75% and 30% pot WHC) and foliage-applied H₂O₂ treatments (15 mM). The drought stress significantly reduced plant growth, relative water contents, chlorophyll and carotenoids contents and increased ROS production (H₂O₂ and O₂^•-) resulting in higher oxidative damage in all quinoa genotypes. Besides, drought stress significantly enhanced the antioxidants (SOD, PPO, and PAL) activity, total soluble sugars, proline, AsA contents and increased the total accumulation of measured inorganic ions in all quinoa genotypes. The PCA analysis indicated that parameters related to osmotic adjustment and antioxidant capacity were more pronounced in 2-Want and IESP genotypes, while parameters depicting oxidative damage were higher in Colorado-407D and more specifically in Pichaman. However, foliage-applied H₂O₂ effectively improved the osmolytes accumulation, antioxidants activity and K⁺/Na⁺ ratio which increased water relations, reduced lipid peroxidation and ultimately resulted in higher plant growth. Overall, 2-Want and IESP genotypes were found relatively more drought resistant, while exogenous application of H₂O₂ can be opted for more improvement in osmotic adjustment and antioxidant system, which may further enhance drought tolerance, even in sensitive genotypes of quinoa, such as Pichaman.

Quinoa Abiotic Stress Responses: A Review

Quinoa (Chenopodium quinoa Willd.) is a genetically diverse Andean crop that has earned special attention worldwide due to its nutritional and health benefits and its ability to adapt to contrasting environments, including nutrient-poor and saline soils and drought stressed marginal agroecosystems. Drought and salinity are the abiotic stresses most studied in quinoa; however, studies of other important stress factors, such as heat, cold, heavy metals, and UV-B light irradiance, are severely limited. In the last few decades, the incidence of abiotic stress has been accentuated by the increase in unpredictable weather patterns. Furthermore, stresses habitually occur as combinations of two or more. The goals of this review are to: (1) provide an in-depth description of the existing knowledge of quinoa's tolerance to different abiotic stressors; (2) summarize quinoa's physiological responses to these stressors; and (3) describe novel advances in molecular tools that can aid our understanding of the mechanisms underlying quinoa's abiotic stress tolerance.

Responses of nonenzymatic antioxidants to atrazine in arbuscular mycorrhizal roots of Medicago sativa L

Atrazine induces the production of reactive oxygen species (ROS), which are detoxified by enzymatic and nonenzymatic mechanisms in plants. Arbuscular mycorrhizal fungi improve on this first level of plant resistance to environmental stresses through the antioxidant defense system, but the way in which nonenzymatic antioxidants relate to atrazine in arbuscular mycorrhizal roots is not well-known. In this study, a symbiotic relationship between Funneliformis mosseae and Medicago sativa L. roots was established successfully. Then, a non-targeted metabolite analysis which was hypothesis-free concerning particular metabolites was used to provide a comprehensive metabolic fingerprint and to subsequently identify, quantify, and finally find different nonenzymatic antioxidants in mycorrhizal and non-mycorrhizal roots following atrazine addition. Tocotrienol, (iso)flavonoids, and their derivate concentrations in F. mosseae-M. sativa mycorrhizal roots were significantly higher than in non-mycorrhizal roots. The majority of (iso)flavonoids and their derivates increased significantly via methylation or glycosylation, but dehydroascorbic acid in its oxidized form decreased significantly in mycorrhizal roots. In general, F. mosseae colonization results in significantly greater nonenzymatic antioxidant tocotrienol and (iso)flavonoids derivate concentrations in M. sativa roots, which may be associated with resistance to atrazine.

Exogenously applied zinc and copper mitigate salinity effect in maize (Zea mays L.) by improving key physiological and biochemical attributes

Zinc or copper deficiency and salinity are known soil problems and often occur simultaneously in agriculture soils. Plants undergo various changes in physiological and biochemical processes to respond to high salt in the growing medium. There is lack of information on the relation of exogenous application of Zn and Cu with important salinity tolerance mechanisms in plants. Therefore, the present study was conducted to determine the effect of foliar Zn and Cu on two maize cultivars (salt-tolerant cv. Yousafwala Hybrid and salt-sensitive cv. Hybrid 1898). Salinity caused a significant reduction in water and turgor potentials, stomatal conductance, and transpiration and photosynthetic rate, while increase in glycine betaine, proline, total soluble sugars, and total free amino acids was evident in plants under saline regimes. Furthermore, there was significant decline in P, N, Ca, K, Mn, Fe, Zn, and Cu and increase in Na and Cl contents in plants fed with NaCl salinity. Nitrate reductase activity was lower in salt-stressed plants. However, foliar application of Zn and Cu circumvented salinity effect on water relations, photosynthesis, and nutrition and this was attributed to the better antioxidant system and enhanced accumulation of glycine betaine, proline, total free amino acids, and sugars. The results of the present study suggested that Zn application was superior to Cu for mediating plant defense responses under salinity.