Dose-Dependent Effects of Coronatine on Cotton Seedling Growth Under Salt Stress

Coronatine (COR) is a chlorosis-inducing, non-host-specific phytotoxin produced by several members of the Pseudomonas syringae group of pathovars. It acts as a molecular mimic of methyl jasmonate. This study investigated the dose-dependent effects of COR on cotton seedling (Gossypium hirsutum L. cv. CCRI 45) growth under normal or salt-stressed conditions. The results demonstrated that salt stress inhibited growth of cotton seedlings, decreased chlorophyll content and net photosynthesis, altered activity of antioxidant enzymes (Superoxide dismutase, Catalase, and peroxidases), and ion balance within the stressed seedlings. Pretreatment with a low concentration of COR (0.01 μmol/L) increased seedling biomass under unstressed and salt-stressed conditions by increasing chlorophyll contents, net photosynthesis and PSII function, elevating the activity of antioxidative enzymes and protein content, improving Na+ exclusion, K+ retention, and the K+/Na+ ratio, and reducing lipid peroxidation causing membrane damage. However, high concentrations of COR (1 μmol/L) decreased seedling biomass under unstressed conditions, and exacerbated the above-mentioned adverse effects of salt stress by inhibiting the activity of antioxidative enzymes and photosynthesis, enhancing chlorophyll degradation and lipid peroxidation causing membrane damage. These results indicated that COR has dose-dependent effects on cotton growth. A low concentration (0.01 μmol/L) of COR improved seedling growth and alleviated the inhibition due to salt stress. However, a higher concentration (1 μmol/L) of COR inhibited seedling growth and aggravated salt stress in cotton seedling under salt-stressed conditions.