Mitigating effects of Methyl Jasmonate on photosynthetic inhibition and oxidative stress of pepper (Capsicum annuum L) seedlings under low temperature combined with low light

Low temperature combined with low light (LL) is a critical abiotic stress that restricting plant growth and yield of pepper (Capsicum annuum L.). Methyl jasmonate (MeJA) is considered with potential benefits for improving plant stress resistance; however, the physiological mechanisms underlying the adaptation of pepper to LL stress have not been explored. This study aimed to investigate the potential mitigating effects of foliar MeJA (200 μmol L⁻¹) application on pepper seedlings subjected to LL stress (10/5 °C, 100 μmol m⁻² s⁻¹) for 168 h. Our results indicated that the application of exogenous MeJA reduced the negative effect on growth inhibition of pepper seedlings caused by LL stress, significantly increased chlorophyll contents and photosynthetic capacity as a result of improved photosynthesis rate. In addition, MeJA reduced the accumulation of reactive oxygen species and malondialdehyde contents induced by LL stress, while enhancing the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase as a result of upregulated expression levels of antioxidant enzyme genes (CaSOD, CaPOD, CaCAT, CaAPX, CaGR, CaDHAR, and CaMDHAR). Additionally, it increased the ascorbic acid and reduced glutathione content, while reducing oxidized glutathione content, thereby preventing membrane lipid peroxidation and protecting plants from oxidative damage under LL stress. Furthermore, seedlings treated with MeJA exhibited significantly enhanced soluble sugar and soluble protein contents in leaves. Taken together, present findings indicate that MeJA application may serve as an effective strategy for mitigating LL-induced oxidative stress by maintaining plant growth, enhancing chlorophyll fluorescence, upregulating the antioxidant defence system, optimizing ascorbate-glutathione cycle, and osmotic adjustment.