Growth, Physiological and Biochemical Responses of Pepper to Flooding Stress: Modulatory Effects of Exogenous Nitric Oxide

Flooding stress is a major abiotic factor limiting plant growth and productivity by disrupting physiological processes and inducing oxidative stress. Nitric oxide (NO) acts as a key signaling molecule regulating stress tolerance mechanisms in plants. This study evaluated the growth, physiological, and biochemical responses of pepper (Capsicum annuum L.) under flooding stress and the potential regulatory role of exogenous NO. Pepper seedlings were exposed to flooding for 10 days, and NO was applied at 0, 50, 100, 150, and 200 µM. Growth, physiological traits, and biochemical parameters were subsequently analyzed. Flooding significantly reduced plant growth and physiological performance. Compared with flooding alone, 100 µM NO increased aboveground fresh weight and chlorophyll a content by 10.3% and 24.2%, respectively, whereas 50 µM NO reduced H2O2 accumulation by 41.6%. Furthermore, 50 and 100 µM NO increased CAT activity by 91.4% and 108.9%, respectively, indicating a marked enhancement of antioxidant defense. Multivariate analyses revealed strong relationships among growth, physiological, and biochemical parameters, linking flooding stress with oxidative stress markers and antioxidant responses. Overall, NO treatments at 50 and 100 µM were most effective in alleviating stress effects and promoting plant growth. These findings demonstrate that exogenous NO plays an important role in regulating physiological and biochemical responses to flooding stress in pepper.