Modulatory role of nitric oxide in cobalt-induced stress in two lettuce (lactuca sativa l.) varieties: a physiological approach

Cobalt (Co) toxicity poses a serious constraint on plant growth by inducing oxidative stress and disrupting cellular and physiological processes. This study investigated the interactive effects of Co and sodium nitroprusside (SNP), a nitric oxide (NO) donor, on two lettuce varieties ( Lactuca sativa L.): curly (var. crispa ) and Romaine (var. longifolia ) under controlled hydroponic conditions. Plants were exposed to Co and SNP treatments, and growth parameters, oxidative stress indicators, antioxidant enzyme activities, and Co accumulation in roots and shoots were evaluated. Co exposure markedly reduced shoot and root biomass and increased membrane permeability, hydrogen peroxide (H 2 O 2 ), malondialdehyde (MDA), proline accumulation, and Co concentrations in both varieties. Co+SNP application partially alleviated Co-induced stress relative to Co treatment alone, as evidenced by moderated membrane permeability (MP), reduced lipid peroxidation (MDA), and modulation of antioxidant enzyme activities (CAT and APX), particularly in Romaine lettuce. In contrast, the response of curly lettuce to SNP application was limited, likely due to its higher Co accumulation and greater oxidative burden. Overall, the results demonstrate genotype-dependent responses to SNP application under high-dose Co stress. Although SNP modulated several stress-related parameters, Co accumulation in edible shoot tissues highlights potential food safety concerns. Therefore, the findings should be interpreted within the context of controlled hydroponic systems and provide insight into genotype-dependent stress responses rather than recommendations for food production in Co-contaminated environments.