Exogenous MeJA-induced chlorosis and senescence in flue-cured tobacco: concentration-dependent effects and transcriptomic analysis

Jasmonic acid (JA) is a common endogenous plant hormone that plays a crucial role in stress resistance and senescence regulation. However, systematic studies on whether a concentration-dependent effect of methyl jasmonate (MeJA) exists in inducing senescence in flue-cured tobacco are lack. This study aimed to investigate the concentration-dependent effects and molecular mechanisms of exogenous MeJA on leaf senescence in topped flue-cured tobacco. Tobacco plants were treated with varying concentrations of MeJA (0.1 mM, 1 mM, 5 mM, and 10 mM), and changes in chlorosis, pigment content, antioxidant enzyme activity, and carbohydrate distribution were observed. Results showed that 5 mM MeJA significantly accelerated leaf senescence, reducing chlorophyll and carotenoid levels, enhancing superoxide dismutase (SOD) and catalase (CAT) activities, and promoting resistance metabolism by decreasing soluble sugar content and increasing structural polysaccharide levels. In contrast, 10 mM MeJA exhibited toxic effects. Transcriptomic analysis revealed that MeJA treatment upregulated genes involved in pathways such as autophagy and flavonoid biosynthesis, while downregulating genes involved in photosynthesis and carbon metabolism. This study unveils the molecular mechanisms through which MeJA induces tobacco leaf senescence by modulating carbohydrate allocation, inhibiting pigment synthesis and photosynthesis, and interacting with ethylene metabolism. These findings provide novel insights for optimizing crop growth regulation.