Integrative application of silicon and/or proline improves Sweet corn (Zea mays L. saccharata) production and antioxidant defense system under salt stress condition.

Silicon (Si) and/or proline (Pro) are natural supplements that are considered to induce plants' stress tolerance against various abiotic stresses. Sweet corn (Zea mays L. saccharata) production is severely afflicted by salinity stress. Therefore, two field tests were conducted to evaluate the potential effects of Si and/or Pro (6mM) used as seed soaking (SS) and/or foliar spray (FS) on Sweet corn plant growth and yield, physio-biochemical attributes, and antioxidant defense systems grown in a saline (EC = 7.14dS m-1) soil. The Si and/or Pro significantly increased growth and yield, photosynthetic pigments, free proline, total soluble sugars (TSS), K+/Na+ratios, relative water content (RWC), membrane stability index (MSI), α-Tocopherol (α-TOC), Ascorbate (AsA), glutathione (GSH), enzymatic antioxidants activities and other anatomical features as compared to controls. In contrast, electrolytes, such as SS and/or FS under salt stress compared to controls (SS and FS using tap water) were significantly decreased. The best results were obtained when SS was combined with FS via Si or Pro. These alterations are brought about by the exogenous application of Si and/or Pro rendering these elements potentially useful in aiding sweet corn plants to acclimate successfully to saline soil.

Glutathione-mediated changes in productivity, photosynthetic efficiency, osmolytes, and antioxidant capacity of common beans (Phaseolus vulgaris) grown under water deficit.

Globally, salinity and drought are severe abiotic stresses that presently threaten vegetable production. This study investigates the potential exogenously-applied glutathione (GSH) to relieve water deficits on Phaseolus vulgaris plants cultivated in saline soil conditions (6.22 dS m-1) by evaluating agronomic, stability index of membrane, water satatus, osmolytes, and antioxidant capacity responses. During two open field growing seasons (2017 and 2018), foliar spraying of glutathione (GSH) at 0.5 (GSH1) or 1.0 (GSH1) mM and three irrigation rates (I100 = 100%, I80 = 80% and I60 = 60% of the crop evapotranspiration) were applied to common bean plants. Water deficits significantly decreased common bean growth, green pods yield, integrity of the membranes, plant water status, SPAD chlorophyll index, and photosynthetic capacity (Fv/Fm, PI), while not improving the irrigation use efficiency (IUE) compared to full irrigation. Foliar-applied GSH markedly lessened drought-induced damages to bean plants, by enhancing the above variables. The integrative I80 + GSH1 or GSH2 and I60 + GSH1 or GSH2 elevated the IUE and exceeded the full irrigation without GSH application (I100) treatment by 38% and 37%, and 33% and 28%, respectively. Drought stress increased proline and total soluble sugars content while decreased the total free amino acids content. However, GSH-supplemented drought-stressed plants mediated further increases in all analyzed osmolytes contents. Exogenous GSH enhanced the common bean antioxidative machinery, being promoted the glutathione and ascorbic acid content as well as up-regulated the activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione peroxidase. These findings demonstrate the efficacy of exogenous GSH in alleviating water deficit in bean plants cultivated in salty soil.

Interplay of silymarin and clove fruit extract effectively enhances cadmium stress tolerance in wheat (Triticum aestivum).

Introduction: Osmoprotectant supplementation can be used as a useful approach to enhance plant stress tolerance. However, the effect of silymarin and clove fruit extract (CFE) on wheat plants grown under cadmium (Cd) stress has not been studied. Methods: Wheat seeds were planted in plastic pots filled with ions-free sand. A ½-strength Hoagland's nutrient solution was used for irrigation. Pots were treated with eight treatments thirteen days after sowing: 1) Control, 2) 0.5 mM silymarin foliar application [silymarin], 3) 2% CFE foliar application [CFE], 4) CFE enriched with silymarin (0.24 g silymarin L-1 of CFE) [CFE-silymarin], 5) Watering wheat seedlings with a nutritious solution of 2 mM Cd [Cd]. 6) Cadmium + silymarin, 7) Cadmium + CFE, and 8) Cadmium + CFE-silymarin. The experimental design was a completely randomized design with nine replicates. Results and discussion: The Cd stress decreased grain yield, shoot dry weight, leaf area, carotenoids, chlorophylls, stomatal conductance, net photosynthetic rate, transpiration rate, membrane stability index, nitrogen, phosphorus, and potassium content by 66.9, 60.6, 56.7, 23.8, 33.5, 48.1, 41.2, 48.7, 42.5, 24.1, 39.9, and 24.1%, respectively. On the other hand, Cd has an Application of CFE, silymarin, or CEF-silymarin for wheat plants grown under Cd stress, significantly improved all investigated biochemical, morphological, and physiological variables and enhanced the antioxidant enzyme activities. Applying CFE and/or silymarin enhanced plant tolerance to Cd stress more efficiently. Our findings suggest using CFE-silymarin as a meaningful biostimulator for wheat plants to increase wheat plants' tolerance to Cd stress via enhancing various metabolic and physiological processes.

Spirulina platensis extract improves the production and defenses of the common bean grown in a heavy metals-contaminated saline soil.

Plants have to cope with several abiotic stresses, including salinity and heavy metals (HMs). Under these stresses, several extracts have been used as effective natural biostimulants, however, the use of Spirulina platensis (SP) extract (SPE) remains elusive. The effects of SPE were evaluated as soil addition (SA) and/or foliar spraying (FS) on antioxidant defenses and HMs content of common bean grown in saline soil contaminated with HMs. Individual (40 or 80 mg SPE/hill added as SA or 20 or 40 mg SPE/plant added as FS) or integrative (SA+FS) applications of SPE showed significant improvements in the following order: SA-80+FS-40 > SA-80+FS-20 > SA-40+FS-40 > SA-40+FS-20 > SA-80 > SA-40 > FS-40 > FS-20 > control. Therefore, the integrative SA+FS with 40 mg SP/plant was the most effective treatment in increasing plant growth and production, overcoming stress effects and minimizing contamination of the edible part. It significantly increased plant growth (74%-185%) and yield (107%-227%) by enhancing net photosynthetic rate (78.5%), stomatal conductance (104%), transpiration rate (124%), and contents of carotenoids (60.0%), chlorophylls (49%-51%), and NPK (271%-366%). These results were concurrent with the marked reductions in malondialdehyde (61.6%), hydrogen peroxide (42.2%), nickel (91%-94%), lead (80%-9%), and cadmium (74%-91%) contents due to the improved contents of glutathione (87.1%), ascorbate (37.0%), and α-tocopherol (77.2%), and the activities of catalase (18.1%), ascorbate peroxidase (18.3%), superoxide dismutase (192%), and glutathione reductase (52.2%) as reinforcing mechanisms. Therefore, this most effective treatment is recommended to mitigate the stress effects of salinity and HMs on common bean production while minimizing HMs in the edible part.

Silymarin-Enriched Biostimulant Foliar Application Minimizes the Toxicity of Cadmium in Maize by Suppressing Oxidative Stress and Elevating Antioxidant Gene Expression.

For maize, the potential preventive role of foliar spraying with an extract derived from maize grain (MEg, 2%), silymarin (Sm, 0.5 mM), or silymarin-enriched MEg (MEg-Sm) in attenuating the stress effects of cadmium (Cd, 0.5 mM) was examined using a completely randomized design layout. Under normal conditions, foliar spraying with MEg, Sm, or MEg-Sm was beneficial (with MEg-Sm preferred) for maize plants, whereas the benefit was more pronounced under Cd stress. The use of Cd through irrigation water decreased plant growth traits, photosynthetic efficiency, including instantaneous carboxylation efficiency, Fv/Fm, and pigment contents, and hormonal contents (e.g., auxin, gibberellins, cytokinins including trans-zeatin, and salicylic acid). These undesired findings were due to an increase in Cd content, leading to increased levels of oxidative stress (O2•- and H2O2), ionic leakage, and lipid peroxidation. Therefore, this damage resulted in an increase in the activities of nonenzymatic antioxidants, Sm, antioxidative enzymes, and enzyme gene expression. However, under Cd stress, although foliar spray with MEg or Sm had better findings than control, MEg-Sm had better findings than MEg or Sm. Application of MEg-Sm greatly increased photosynthesis efficiency, restored hormonal homeostasis, and further increased the activities of various antioxidants, Sm, antioxidative enzymes, and enzyme gene expression. These desired findings were due to the suppression of the Cd content, and thus the levels of O2•-, H2O2, ionic leakage, and lipid peroxidation, which were positively reflected in the growth and accumulation of dry matter in maize plants. The data obtained in this study recommend applying silymarin-enriched maize grain extract (MEg-Sm at 0.24 g Sm L-1 of MEg) as a spray solution to maize plants when exposed to excess Cd in soil or irrigation water.

Foliar Application of Zinc Oxide Nanoparticles Promotes Drought Stress Tolerance in Eggplant (Solanum melongena L.).

Water shortage and salinity are major challenges for sustaining global food security. Using nutrients in the nano-scale formulation including zinc oxide nanoparticles (ZnO NP) is a novel fertilization strategy for crops. In this study, two field-based trials were conducted during 2018 and 2019 to examine the influence of three ZnO NP concentrations (0, 50, and 100 ppm) in eggplant grown under full irrigation (100 of crop evapotranspiration; ETc) and drought stress (60% of ETc). Plant growth, yield, water productivity (WP), physiology, biochemistry, and anatomy responses were evaluated. Drought stress significantly decreased membrane stability index (MSI), relative water content (RWC), and photosynthetic efficiency, thus hampered eggplant growth and yield. In contrast, exogenous ZnO NP to water-stressed eggplant resulted in increased RWC and MSI associated with improved stem and leaf anatomical structures and enhanced photosynthetic efficiency. Under drought stress, supplementation of 50 and 100 ppm ZnO NP improved growth characteristics and increased fruit yield by 12.2% and 22.6%, respectively, compared with fully irrigated plants and nonapplied ZnO NP. The highest water productivity (WP) was obtained when eggplant was irrigated with 60% ETc and foliarly treated with 50 or 100 ppm of ZnO NP, which led to 50.8-66.1% increases in WP when compared with nontreated fully irrigated plants. Collectively, these findings demonstrated that foliar spraying ZnO NP gives the utility for alleviating drought stress effects on eggplant cultivated in saline soil.

Sequenced application of glutathione as an antioxidant with an organic biostimulant improves physiological and metabolic adaptation to salinity in wheat.

Globally, salinity threatens the agricultural crops productivity by inhibiting plant growth and development through osmotic stress and ionic cytotoxicity. The polygenic nature of salinity offers several pragmatic shotgun approaches to improve salinity tolerance. The present study investigated the potential of glutathione (GSH; 1 mM) as an antioxidant and moringa leaf extract (MLE; 3%) as an organic biostimulant applied in sequence as seed priming and foliar spray on wheat growth, physiology and metabolic adaptation under saline conditions (9.16 dS m-1). Plants without any treatment and water spray (H2O) were considered controls. Salinity induced osmotic stress reduced the plant tissue water status and photosynthetic performance, and perturbed ionic (K+/Na+, Ca2+/Na+, K++Ca2+/Na+) and hormonal (IAA, GA3, zeatin, ABA) homeostasis, consequently affected growth and yield in wheat. Sequenced applied MLE and/or GSH improved osmotic stress tolerance by stabilizing membrane integrity and decreasing electrolyte leakage. These positive results were owed to enhanced endogenous GSH and ascorbate levels. Improved tissue water status was attributed to increased osmotic adjustment, better ionic and hormonal homeostasis contributed to improving photosynthetic efficiency and growth under salinity. Exogenously applied MLE and GSH sequences improved grain yield, which was attributed to the maintenance of green leaf area and delayed senescence associated with an increase in photosynthetic pigments and chlorophyll fluorescence traits. In crux, exogenous applied MLE and/or GSH can be the best physiological strategy to reduce the deleterious effects of salinity and improve physiological and metabolic adaptation in wheat under saline field conditions.

Stimulating antioxidant defenses, antioxidant gene expression, and salt tolerance in Pisum sativum seedling by pretreatment using licorice root extract (LRE) as an organic biostimulant.

Plant extracts have recently been used as exogenous adjuvants to strengthen the endogenous plant defense systems when they grow under different environmental stresses, including salinity. The study aimed at determining the effects of seed soaking using licorice root extract (LRE) on photosynthesis and antioxidant defense systems, including transcript levels of enzyme-encoding genes in pea seedling grown under 150 mM NaCl-salinity. Salt stress reduced seedling growth, photosynthesis attributes, and K+ content, and increased oxidative stress (O2•‒ and H2O2, and MDA), Na+, and Cl-, along with an increase in antioxidative defense activities compared to control. However, LRE pretreatment enhanced seedling growth, photosynthetic attributes (chlorophylls, carotenoids, Fv/Fm, Pn, Tr, and gs), ascorbate and glutathione and their redox states, proline, soluble sugars, α-TOC, and enzyme activities compared to stressed control. LRE pretreatment also upregulated transcript levels of CAT-, SOD-, APX-, GR-, DHAR-, and PrxQ-encoding genes in salt-stressed seedlings, decreasing oxidative stress and Na+ and Cl- contents and increasing K+ content and K+/Na+ ratio.

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

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

Interplaying roles of silicon and proline effectively improve salt and cadmium stress tolerance in Phaseolus vulgaris plant.

The interplaying defensive roles of silicon (Si) and proline (Pro) in improving growth and yield attributes, physio-biochemical attributes, and antioxidant defense systems in common bean plant grown under saline (NaCl) and/or cadmium (Cd2+) stress were assessed. Seed were sown in plastic pots filled with sand-free ions as a growing medium that watered with a ½-strength Hoagland's nutrient solution. Twenty five days after planting, pots were split into 4 plots; control (no stress), 150 mM NaCl (salt stress), 1.5 mM Cd2+ in CdCl2 (Cd2+ stress), and 100 mM NaCl + 1.0 mM Cd2+ (salt + Cd2+ stress). Four treatments; foliar spray with distilled water, 6 mM Si (in K2SiO3.nH2O) solution, 6 mM Pro solution, and a combination of Si and Pro were allotted under each of the 4 plots. The experimental layout was a completely randomized design with 15 replicates. Compared to control, NaCl or Cd2+ stress significantly (P ≤ 0.05) reduced plant growth and yield attributes, leaf contents of chlorophylls, carotenoids, N, P, and K+, K+/Na+ ratio, RWC, MSI, Pn and Tr, while elevated significantly leaf EL, leaf contents of proline, soluble sugar, glutathione, MDA, Na+, and root, leaf and pod contents of Cd2+. The activities of antioxidant enzymes were also raised. The combined stress (NaCl + Cd2+) was more influential. Addition of Si and/or Pro for common bean plants under NaCl and/or Cd2+ stress significantly enhanced all investigated attributes of physiology, morphology, and biochemistry, and further increased the activities of antioxidant enzymes. Supplementation of Si + Pro was the best treatment having more positive influential, especially reducing the Cd2+ content in Phaseolus vulgaris pods to the limits (0.27 mg kg-1) for legumes. Therefore, this combined treatment is recommended to use for alleviating environmental stress effects, especially salinity and Cd2+ for common bean production.

Integrative moringa and licorice extracts application improves Capsicum annuum fruit yield and declines its contaminant contents on a heavy metals-contaminated saline soil.

Green approaches for improving plant performance using natural supplementations are highly seeking. Following a preliminary study conducted on contaminated saline (EC = 7.75 dS m-1) and normal (EC = 1.4 dS m-1) soils, two main field trials were conducted to study the potential effects of licorice root (LRE; 0.5%) and moringa seed (MSE; 0.5%) extracts, supplemented to soil through irrigation water (SA) and/or as foliar spray (FS), on performance, physio-biochemical components, antioxidant defense system, and contaminants contents of Capsicum annuum plants grown on heavy metals-contaminated saline soil. Both extracts were applied in single treatments such as LRE-SA, MSE-SA, LRE-FS, and MSE-FS or in integrations like LRE-SA+LRE-FS, LRE-SA+MSE-FS, MSE-SA+LRE-FS, and MSE-SA+MSE-FS. The preliminary study results showed significant reductions in plant performance (growth and yield), chlorophylls content and significant increase in Cd content due to heavy metals and salt stress. However, LRE and MSE applied singly or in combinations positively modified these parameters compared to the control (SA and FS were applied with tap water). On the other hand, these parameters were not responded to LRE and/or MSE applications on the normal soil. The main studies results showed that all single or integrative treatments significantly increased plant growth and yield, leaf contents of leaf photosynthetic pigments, free proline, total soluble sugars, N, P, and K+, ratio of K+/Na+, and activities of CAT, POX, APX, SOD, and GR. In contrast, contaminants; Na+, Cd, Cu, Pb and Ni contents in plant leaves and fruits were significantly reduced on heavy metals-contaminated saline soil compared to the control. Additionally, all integrative treatments significantly exceeded all single treatments in this concern. The integrative MSE-SA+LRE-FS was the best treatment that is recommended to be used to maximize pepper plant performances and minimize plant contaminant contents on contaminated saline soils.

The defensive role of silicon in wheat against stress conditions induced by drought, salinity or cadmium.

In the crust of earth, silicon (Si) is one of the two major elements. For plant growth and development, importance of Si remains controversial due to the widely differences in ability of plants to take up this element. In this paper, pot experiments were done to study Si roles in improving salt, drought or cadmium (Cd) stress tolerance in wheat. Up to full emergence, all pots were watered at 100% field capacity (FC) every other day with nutrient solution without any treatments. Fifteen days after sowing, pots were divided into four plots, each with 40 pots for no stress (control) and three stress treatments; drought (50% FC), salinity (200 mM NaCl) and cadmium (2 mM Cd). For all plots, Si was applied at four levels (0, 2, 4 and 6 mM). Under no stress condition, Si applications increased Si content and improved growth as a result of reduced electrolyte leakage (EL), malondialdehyde (MDA) and Na+ contents. Under stress conditions, Si supplementation conferred higher growth, gas exchange, tissue water and membranes stabilities, and K+ content, and had limited MDA and Na+ contents and EL compared to those obtained without Si. Compared to those without Si, enzyme (e.g., superoxide dismutase, catalase and peroxidase) activity was improved by Si applications, which were linked with elevated antioxidants and osmoprotectants (e.g., free proline, soluble sugars, ascorbic acid and glutathione) contents, might providing antioxidant defense against abiotic stress in wheat. The level of 4 mM Si was most effective for mitigating the salt and drought stress conditions, while 6 mM Si level was most influentially for alleviating the Cd stress condition. These results suggest that Si is beneficial in remarkably affecting physiological phenomena and improving wheat growth under abiotic stress.