Mitigation of Salinity Stress in Rice Seedlings by Paclobutrazol: A Physiological-Biochemical Approach

Salinity poses a serious constraint on rice (Oryza sativa L.) productivity in both coastal and arid irrigated regions, with early growth stages such as seedling establishment being particularly vulnerable. In this study, rice seedlings of cv. Sakha 177 were exposed to diluted seawater at 2000 and 4000 mg/L, and their growth traits, relative water content, pigment composition, photosynthetic performance, and enzyme activities were assessed against non-salinized controls. Salt stress led to marked reductions in seedling height, leaf area, relative water content, and the contents of chlorophylls a and b and carotenoids, while promoting the accumulation of hydrogen peroxide, superoxide anions, and malondialdehyde. Paclobutrazol (PBZ) application at 100 mg/L alleviated these adverse effects by increasing chlorophyll and carotenoid pigments, enhancing the photosynthetic rate, and stimulating antioxidant enzymes (SOD, CAT, POD and APX). This enzymatic boost contributed to lower concentrations of hydrogen peroxide, superoxide radicals, and malondialdehyde, thereby strengthening the seedlings’ overall tolerance to salinity. These results emphasize the effectiveness of PBZ at 100 mg/L in mitigating the harmful impacts associated with prolonged irrigation using saline water.