Drought Stress Alleviator Melatonin Reconfigures Water-Stressed Barley (Hordeum vulgare L.) Plants' Photosynthetic Efficiency, Antioxidant Capacity, and Endogenous Phytohormone Profile

The production of crops is severely limited by water scarcity. We still do not fully understand the underlying mechanism of exogenous melatonin (MT)-mediated water stress tolerance in barley. This study is the first of its kind to show how MT can potentially mitigate changes in barley's physio-biochemical parameters caused by water deficiency. Barley was grown under three irrigation levels (100%, 70%, and 30% of field capacity) and was foliar sprayed with 70 μM MT. The results showed that exogenously applied MT protected the photosynthetic apparatus by improving photosynthetic pigment content, photochemical reactions of photosynthesis, Calvin cycle enzyme activity, gas exchange capacity, chlorophyll fluorescence system, and membrane stability index. Furthermore, the increased levels of salicylic acid, gibberellins, cytokinins, melatonin, and indole-3-acetic acid, as well as a decrease in abscisic acid, indicated that foliar-applied MT greatly improved barley water stress tolerance. Additionally, by increasing the activity of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and decreasing hydrogen peroxide content, lipid peroxidation, and electrolyte leakage, MT application lessened water stress-induced oxidative stress. According to the newly discovered data, MT application improves barley water stress tolerance by reprogramming endogenous plant hormone production and antioxidant activity, which enhances membrane stability and photosynthesis. This study unraveled MT's crucial role in water deficiency mitigation, which can thus be applied to water stress management.

Spermine-Salicylic Acid Interplay Restrains Salt Toxicity in Wheat (Triticum aestivum L.)

Spermine (SPM) and salicylic acid (SA) are plant growth regulators, eliciting specific responses against salt toxicity. In this study, the potential role of 30 mgL^-1 SPM and/or 100 mgL^-1 SA in preventing salt damage was investigated. Wheat plants were grown under non-saline or saline conditions (6.0 and 12.0 dS m^-1) with and without SA and/or SPM foliar applications. Exogenously applied SA and/or SPM alleviated the inhibition of plant growth and productivity under saline conditions by increasing Calvin cycle enzyme activity. Foliage applications also improved ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities, which effectively scavenged hydrogen peroxide and superoxide radicals in stressed plants. Furthermore, foliar treatments increased antioxidants such as ascorbate and glutathione, which effectively detoxified reactive oxygen species (ROS). Exogenous applications also increased N, P, and K⁺ acquisition, roots' ATP content, and H⁺-pump activity, accompanied by significantly lower Na⁺ accumulation in stressed plants. Under saline environments, exogenous SA and/or SPM applications raised endogenous SA and SPM levels. Co-application of SA and SPM gave the best response. The newly discovered data suggest that the increased activities of Calvin cycle enzymes, root H⁺-pump, and antioxidant defense machinery in treated plants are a mechanism for salt tolerance. Therefore, combining the use of SA and SPM can be a superior method for reducing salt toxicity in sustainable agricultural systems.

Plant Growth Stimulators Improve Two Wheat Cultivars Salt-Tolerance: Insights into Their Physiological and Nutritional Responses

Spermine (SPM) and salicylic acid (SA), plant growth stimulators, are involved in various biological processes and responses to environmental cues in plants. However, the function of their combined treatment on wheat salt tolerance is unclear. In this study, wheat (Triticum aestivum L. cvs. Shandawel 1 and Sids 14) plants were grown under non-saline and saline (6.0 and 12.0 dS m^-1) conditions and were foliar sprayed with 100 mgL^-1 SA and/or 30 mgL^-1 SPM. Exogenously applied SA and/or SPM relieved the adverse effects caused by salt stress and significantly improved wheat growth and production by inducing higher photosynthetic pigment (chlorophyll a, chlorophyll b, carotenoids) content, nutrient (N, P, K⁺, Ca²⁺, Mg²⁺, Fe, Zn, Cu) acquisition, ionic (K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺) homeostatics, osmolyte (soluble sugars, free amino acids, proline, glycinebetaine) accumulation, protein content, along with significantly lower Na⁺ accumulation and chlorophyll a/b ratio. The best response was registered with SA and SPM combined treatment, especially in Shandawel 1. This study highlighted the recovery impact of SA and SPM combined treatment on salinity-damaged wheat plants. The newly discovered data demonstrate that this treatment significantly improved the photosynthetic pigment content, mineral homeostasis, and osmoprotector solutes buildup in salinity-damaged wheat plants. Therefore, it can be a better strategy for ameliorating salt toxicity in sustainable agricultural systems.

Synergistic Effects of Salicylic Acid and Melatonin on Modulating Ion Homeostasis in Salt-Stressed Wheat (Triticum aestivum L.) Plants by Enhancing Root H+-Pump Activity

Salicylic acid (SA) and melatonin (MT) have been shown to play important roles in plant salt tolerance. However, the underlying mechanisms of SA-MT-interaction-mediated ionic homeostasis in salt-stressed plants are unknown. As a first investigation, this study aimed to clarify how SA-MT interaction affects H⁺-pump activity in maintaining the desired ion homeostasis under saline conditions and its relation to ROS metabolism. Wheat (Triticum aestivum L.) plants were grown under non-saline or saline conditions and were foliar sprayed with 75 mg L^-1 SA or 70 μM MT. The SA+MT combined treatment significantly increased N, P, K⁺, Fe, Zn, and Cu acquisition, accompanied by significantly lower Na⁺ accumulation in salt-stressed plants compared to non-stressed ones. Additionally, it significantly enhanced ATP content and H⁺-pump activity of the roots. The mitigation was also detected in the reduced superoxide radical content, electrolyte leakage, and lipoxygenase activity, as well as increased superoxide dismutase, catalase, peroxidase, and polyphenol oxidase activities; K⁺/Na⁺, Ca²⁺/Na⁺, and Mg²⁺/Na⁺ ratios; relative water content; membrane stability index; and free amino acid accumulation in treated plants. The novel evidence shows that the higher root H⁺-pump activity in treated plants is a tolerance mechanism that increases the salt tolerance via maintaining ionic homeostasis.

Modulation of Physiological Stress Response of Triticum aestivum L. to Glyphosate by Brassinosteroid Application

The potential of brassinosteroids to modulate the physiological responses of winter wheat (Triticum aestivum L.) to herbicide stress was evaluated. Young winter wheat seedlings were treated with 24-epibrassinolide (EBL) and 24 h later were sprayed with glyphosate. The physiological responses of treated plants were assessed 14 days after herbicide application. Wheat growth was noticeably inhibited by glyphosate. The herbicide application significantly increased the content of the stress markers proline and malondialdehyde (MDA) evidencing oxidative damage. The content of phenolic compounds was decreased in the herbicide-treated plants. Slight activation of superoxide dismutase (SOD) and catalase (CAT) and considerable increase of glutathione reductase (GR) and guaiacol peroxidase (POX) activities were found. Increased POX and glutathione S-transferase (GST) activities were anticipated to be involved in herbicide detoxification. Conjugation with glutathione in herbicide-treated plants could explain the reduction of thiols suggesting unbalanced redox state. EBL application did not alter the plant growth but a moderate activation of antioxidant defense (POX, GR, and CAT activities and phenolic levels) and detoxifying enzyme GST was observed. The hormonal priming provoked a slight decrease in MDA and proline levels. The results demonstrate that EBL-pretreatment partly restored shoot growth and has a potential to mitigate the oxidative damages in glyphosate-treated plants through activation of the enzymatic antioxidant defense and increase of the phenolic compounds.

Effective microorganisms enhance the scavenging capacity of the ascorbate-glutathione cycle in common bean (Phaseolus vulgaris L.) plants grown in salty soils

No information is available regarding effective microorganisms (EM) influence on the enzymatic and non-enzymatic antioxidant defence system involved in the ascorbate-glutathione cycle under saline conditions. Therefore, as a first approach, this article focuses on the contribution of EM to the scavenging capacity of the ascorbate-glutathione cycle in salt-stressed plants. It investigates some mechanisms underlying alleviation of salt toxicity by EM application. Phaseolus vulgaris cv. Nebraska plants were grown under non-saline or saline conditions (2.5 and 5.0 dSm(-1)) with and without EM application. Lipid peroxidation and H2O2 content were significantly increased in response to salinity, while they decreased with EM application in both stressed and non-stressed plants. Activities of ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) increased under saline conditions; these increases were more significant in salt-stressed plants treated by EM. Activities of monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) and dehydroascorbate reductase (DHAR; EC 1.8.5.1) decreased in response to salinity; however, they were significantly increased in stressed plants treated with EM. Ascorbate and glutathione contents were increased with the increasing salt concentration; moreover they further increased in stressed plants treated with EM. Ratios of AsA/DHA and GSH/GSSG decreased under saline conditions, whereas they were significantly increased with EM treatment in the presence or in the absence of soil salinization. The EM treatment detoxified the stress generated by salinity and significantly improved plant growth and productivity. Enhancing the H2O2-scavenging capacity of the ascorbate-glutathione cycle in EM-treated plants may be an efficient mechanism to attenuate the activation of plant defences.

RNAi based simultaneous silencing of all forms of light-dependent NADPH:protochlorophyllide oxidoreductase genes result in the accumulation of protochlorophyllide in tobacco (Nicotiana tabacum)

Conversion of protochlorophyllide (Pchlide) into chlorophyllide (Chlide), a key step in chlorophyll biosynthesis, is mediated by a light-dependent NADPH:protochlorophyllide oxidoreductase (POR). POR exists in multiple isoforms that share high degree of homology. RNAi-mediated gene silencing approach was used to suppress the expression of POR genes in order to study its role in the Chls biosynthesis in tobacco (Nicotiana tabacum L.). The transgenic plants were devoid of chlorophyll pigments and resembled albino plants. Northern blot analysis confirmed the degradation of POR transcripts into 21-23 bp fragments. Pigment analysis showed the accumulation of various intermediate compounds of Chl biosynthesis pathway including Pchlide. However, no trace of chlorophyll was observed. As compared to wild type, POR-silenced plants accumulated larger (60%) amounts of Pchlide from its endogenous substrate. When leaf discs of WT and POR-silenced plants were treated with exogenous ALA both WT and POR-silenced plants accumulated large amounts of tetrapyrrolic intermediates demonstrating that Pchlide biosynthesis potential was not suppressed in POR-silenced plants. Upon illumination, WT plants photo-transformed large amounts of Pchlide to Chlide. However, POR-silenced plants almost completely failed to do so. Results demonstrate that the antisense approaches to drop expression of individual POR isoforms have provided valuable insights into the role of distinct PORs during greening. Moreover, data illustrate that the POR is the only enzyme that can convert the Pchlide to Chlide and there is no alternate enzyme that can substitute the POR in higher plants. Thus, this investigation describes ideal mechanism for the silencing of POR isozymes in tobacco.