Sustainable agriculture is increasingly being put in danger by environmental contamination with dangerous heavy metals (HMs), especially lead (Pb). Plants have developed a sophisticated mechanism for nitric oxide (NO) production and signaling to regulate hazardous effects of abiotic factors, including HMs. In the current study, we investigated the role of exogenously applied sodium nitroprusside (SNP, a nitric oxide (NO) donor) in ameliorating the toxic effects of lead (Pb) on rice. For this purpose, plants were subjected to 1.2 mM Pb alone and in combination with 100 µM SNP. We found that under 1.2 mM Pb stress conditions, the accumulation of oxidative stress markers, including hydrogen peroxide (H₂O₂) (37%), superoxide anion (O₂⁻) (28%), malondialdehyde (MDA) (33%), and electrolyte leakage (EL) (34%), was significantly reduced via the application of 100 µM SNP. On the other hand, under the said stress of Pb, the activity of the reactive oxygen species (ROS) scavengers such as polyphenol oxidase (PPO) (60%), peroxidase (POD) (28%), catalase (CAT) (26%), superoxide dismutase (SOD) (42%), and ascorbate peroxidase (APX) (58%) was significantly increased via the application of 100 µM SNP. In addition, the application of 100 µM SNP rescued agronomic traits such as plant height (24%), number of tillers per plant (40%), and visible green pigments (44%) when the plants were exposed to 1.2 mM Pb stress. Furthermore, after exposure to 1.2 mM Pb stress, the expression of the heavy-metal stress-related genes OsPCS1 (44%), OsPCS2 (74%), OsMTP1 (83%), OsMTP5 (53%), OsMT-I-1a (31%), and OsMT-I-1b (24%) was significantly enhanced via the application of 100 µM SNP. Overall, our research evaluates that exogenously applied 100 mM SNP protects rice plants from the oxidative damage brought on by 1.2 mM Pb stress by lowering oxidative stress markers, enhancing the antioxidant system and the transcript accumulation of HMs stress-related genes.

Heavy metal toxicity, including lead (Pb) toxicity, is increasing in soils, and heavy metals are considered to be toxic in small amounts. Pb contamination is mainly caused by industrialization (e.g., smelting and mining), agricultural practices (e.g., sewage sludge and pests), and urban practices (e.g., lead paint). An excessive concentration of Pb can seriously damage and threaten crop growth. Furthermore, Pb adversely affects plant growth and development by affecting the photosystem, cell membrane integrity, and excessive production of reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) and superoxide (O₂⁻). Nitric oxide (NO) is produced via enzymatic and non-enzymatic antioxidants to scavenge ROS and lipid peroxidation substrates to protect cells from oxidative damage. Thus, NO improves ion homeostasis and confers resistance to metal stress. In the present study, we investigated the effect of exogenously applied NO and S-nitrosoglutathione in soybean plants Our results demonstrated that exogenously applied NO aids in better growth under lead stress due to its ability in sensing, signaling, and stress tolerance in plants under heavy metal stress along with lead stress. In addition, our results showed that S-nitrosoglutathione (GSNO) has a positive effect on soybean seedling growth under lead-induced toxicity and that NO supplementation helps to reduce chlorophyll maturation and relative water content in leaves and roots following strong bursts under lead stress. GSNO supplementation (200 µM and 100 µM) reduced compaction and approximated the oxidative damage of MDA, proline, and H₂O₂. Moreover, under plant stress, GSNO application was found to relieve the oxidative damage by reactive oxygen species (ROS) scavenging. Additionally, modulation of NO and phytochelatins (PCS) after prolonged metal reversing GSNO application confirmed detoxification of ROS induced by the toxic metal lead in soybean. In summary, the detoxification of ROS caused by toxic metal concentrations in soybean is confirmed by using NO, PCS, and traditionally sustained concentrations of metal reversing GSNO application.

Soybean, a major legume crop, has seen a decline in its production owing to challenges in seed germination and the development of seedlings. Thus, in this study, we systematically investigated the influence of various chitosan–S-nitrosoglutathione (chitosan-GSNO) nanoparticle (0, 25, 50, and 100 µM) and Si (0, 0.5, and 1 mM) priming concentrations on soybean seed germination and seedling growth over five different priming durations (range: 1–5 h at each concentration). Significant differences were observed in all parameters, except seedling diameter, with both treatments. Seed germination was significantly enhanced after 3 h of priming in both treatments. The final germination percentage (FGP), peak germination percentage (PGP), vigor index (VI), seedling biomass (SB), hypocotyl length (HL), and radical length (RL) of 100 μM chitosan-GSNO-nanoparticle-primed seeds increased by 20.3%, 41.3%, 78.9%, 25.2%, 15.7%, and 65.9%, respectively, compared with those of the control; however, the mean germination time (MGT) decreased by 18.43%. Si priming at 0.5 mM increased the FGP, PGP, VI, SB, HL, and RL by 13.9%, 55.17%, 39.2%, 6.5%, 22.5%, and 25.1%, respectively, but reduced the MGT by 12.29% compared with the control treatment. Chitosan-GSNO and Si treatment up-regulated the relative expression of gibberellic acid (GA)-related genes (GmGA3ox3 and GmGA2ox1) and down-regulated that of abscisic acid (ABA)-related genes (GmABA2, GmAAO3, and GmNCED5). Chitosan-GSNO and Si application increased bioactive GA₄ levels and simultaneously reduced ABA content. Hence, the use of exogenous chitosan-GSNO nanoparticles and Si as priming agents had a beneficial effect on seed germination and seedling growth because of the up-regulation in the expression of GA and down-regulation in the expression of ABA. Additional research is needed to understand the combined impact of Si and chitosan-GSNO nanoparticles, including their effects on the expression levels of other hormones and genes even in the later growth stage of the crop.

Nitric oxide (NO) and melatonin (MT) significantly influence photosynthetic processes by modulating redox homeostasis, chlorophyll content, stomatal conductance, and gene expression, particularly under abiotic stress conditions. This review summarizes the intricate crosstalk between NO and melatonin, focusing on their coordinated roles in regulating photosynthetic efficiency. Evidence from various plant species indicates that the application of exogenous NO and melatonin enhances chlorophyll content, photosystem efficiency (particularly PSII), and photosynthetic performance, mitigating stress-induced damage. Molecular analysis demonstrates that both molecules influence key photosynthetic gene modulating photosystems I and II, and Calvin cycle activities. Moreover, NO and melatonin collaboratively regulate stomatal movements through ABA, Ca²⁺, and H₂O₂ signaling pathways, involving genes such as PMRT1, CIPKs, and OST1. Experimental data from diverse plant species under stress conditions, including drought, salinity, heavy metals, and flooding, highlight their synergistic protective effects. Exploring these mechanisms further may enable practical agricultural strategies involving combined NO and melatonin treatments to improve crop resilience and productivity under increasingly challenging environmental conditions. Future research directions should emphasize unraveling detailed molecular interactions, enabling targeted biotechnological applications in crop improvement programs for enhanced global food security.

Soil salinity is a major global challenge affecting agricultural productivity and food security. This study explores innovative strategies to improve salt tolerance in soybean (Glycine max), a crucial crop in the global food supply. This study investigates the synergistic effects of S-nitroso glutathione (GSNO) and silicon on enhancing salt tolerance in soybean (Glycine max). Two soybean cultivars, Seonpung (salt-tolerant) and Cheongja (salt-sensitive), were analyzed for various physiological, biochemical, and genetic traits under salt stress. The results showed that the combined GSNO and Si treatment significantly improved several key traits, including plant height, relative water content, root development, nodule numbers, chlorophyll content, and stomatal aperture, under both control and salt stress conditions. Additionally, this treatment optimized ion homeostasis by enhancing the Na/K ratio and Ca content, while reducing damage markers such as electrolyte leakage, malondialdehyde, and hydrogen peroxide. The stress-responsive compounds, including proline, ascorbate peroxidase, and water-soluble proteins, were elevated under stress conditions, indicating improved tolerance. Gene expression analysis revealed significant upregulation of genes such as GmNHX1, GmSOS2, and GmAKT1, associated with salt stress response, while GmNIP2.1, GmNIP2.2, and GmLBR were downregulated in both varieties. Notably, the salt-sensitive variety Cheongja exhibited higher electrolyte leakage and oxidative damage compared to the salt-tolerant Seonpung. These findings suggest that the combination of GSNO and silicon enhances salt tolerance in soybean by improving physiological resilience, ion homeostasis, and stress-responsive gene expression.

Nitrogen fixation in legume nodules is crucial for plant growth and development. Therefore, this study aims to investigate the effects of nitric oxide [S-nitrosoglutathione (GSNO)] and silicon [sodium metasilicate (Si)], both individually and in combination, on soybean growth, nodule formation, leghaemoglobin (Lb) synthesis, and potential post-translational modifications. At the V1 stage, soybean plants were treated for 2 weeks with 150 µM GSNO, and Si at concentrations of 1 mM, 2 mM, and 4 mM. The results showed that NO and Si enhance the nodulation process by increasing phenylalanine ammonia-lyase activity and Nod factors (NIP2-1), attracting rhizobia and accelerating nodule formation. This leads to a greater number and larger diameter of nodules. Individually, NO and Si support the synthesis of Lb and leghaemoglobin protein (Lba) expression, ferric leghaemoglobin reductases (FLbRs), and S-nitrosoglutathione reductase (GSNOR). However, when used in combination, NO and Si inhibit these processes, leading to elevated levels of S-nitrosothiols in the roots and nodules. This combined inhibition may potentially induce post-translational modifications in FLbRs, pivotal for the reduction of Lb³⁺ to Lb²⁺. These findings underscore the critical role of NO and Si in the nodulation process and provide insight into their combined effects on this essential plant function.