Cucumbers, cultivated globally on 3.7 million hectares, face yield losses due to salinity, highlighting the need for effective mitigation strategies for degraded soils. Melatonin (MT) has gained significant interest for its ability to relieve plant stress. To explore the regulatory role of exogenous MT in maintaining redox homeostasis in cucumber seedlings under saline-alkali stress (SA), this study employed the cucumber cultivar 'Xinchun No. 4 '. Simulated saline-alkali conditions were applied, and the effects of exogenous MT on seedling growth, reactive oxygen species (ROS) production, the ascorbate-glutathione (AsA-GSH) cycle, and changes in leaf anatomy were systematically assessed. The findings reveal that exposure to 40 mmol center dot L-1 saline-alkali stress significantly impaired cucumber seedling growth, reduced biomass, and led to excessive accumulation of hydrogen peroxide (H2O2) and superoxide anions (O2 center dot ) in the leaves. This, resulted in increased lipid peroxidation (indicated by elevated malondialdehyde (MDA) levels), whichi further compromised the cell membrane. Application of 10 mu mol center dot L-1 MT effectively reduced ROS levels, lowered MDA content, and mitigated electrolyte leakage. MT also enhanced AsA and GSH levels, improved AsA/DHA and GSH/GSSG ratios, and upregulated key AsA-GSH cycle genes (CsAPX, CsAAO, CsMDAR, CsDHAR, CsGR), leading to a significant increase in enzymatic activity. In addition, MT alleviated stress-induced stomatal closure, thereby restoring normal stomatal function. These findings suggest that MT enhances saline-alkali tolerance by mitigating oxidative damage, promoting antioxidant defenses, and effectively preserving stomatal function. Thus, our study points to a sustainable strategy to improve crop resilience in salinized environments via MT application.

Citrus is mainly cultivated in acid soil with low boron (B) and high copper (Cu). In this study, Citrus sinensis seedlings were submitted to 0.5 (control) or 350 mu M Cu (Cu excess or Cu exposure) and 2.5, 10, or 25 mu M B for 24 weeks. Thereafter, H2O2 production rate (HPR), superoxide production rate (SAPR), malondialdehyde, methylglyoxal, and reactive oxygen species (ROS) and methylglyoxal detoxification systems were measured in leaves and roots in order to test the hypothesis that B addition mitigated Cu excess-induced oxidative damage in leaves and roots by reducing the Cu excess-induced formation and accumulation of ROS and MG and by counteracting the impairments of Cu excess on ROS and methylglyoxal detoxification systems. Cu and B treatments displayed an interactive influence on ROS and methylglyoxal formation and their detoxification systems. Cu excess increased the HPR, SAPR, methylglyoxal level, and malondialdehyde level by 10.9% (54.3%), 38.9% (31.4%), 50.3% (24.9%), and 312.4% (585.4%), respectively, in leaves (roots) of 2.5 mu M B-treated seedlings, while it only increased the malondialdehyde level by 48.5% (97.8%) in leaves (roots) of 25 mu M B-treated seedlings. Additionally, B addition counteracted the impairments of Cu excess on antioxidant enzymes, ascorbate-glutathione cycle, sulfur metabolism-related enzymes, sulfur-containing compounds, and methylglyoxal detoxification system, thereby protecting the leaves and roots of Cu-exposed seedlings against oxidative damage via the coordinated actions of ROS and methylglyoxal removal systems. Our findings corroborated the hypothesis that B addition alleviated Cu excess-induced oxidative damage in leaves and roots by decreasing the Cu excess-induced formation and accumulation of ROS and MG and by lessening the impairments of Cu excess on their detoxification systems. Further analysis indicated that the pathways involved in the B-induced amelioration of oxidative stress caused by Cu excess differed between leaves and roots.