Effects of sucrose and 1-MCP on enzymatic and nonenzymatic antioxidants in postharvest Gynura bicolor DC

Abstract

After harvesting, Gynura bicolor DC (G. bicolor) undergoes rapid quality deterioration, including decay, nutrient loss, and reactive oxygen species (ROS) burst, greatly limiting its shelf life. This study was performed to evaluate the effects of treatment with sucrose and 1-methylcyclopropene (1-MCP) on indices of quality deterioration, ROS metabolism, and phenylpropanoid metabolism, with the goals of resisting oxidative stress and improving the postharvest quality of G. bicolor. Sucrose treatment activated phenylpropanoid metabolism, increased phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate:CoA ligase (4CL) activities, and promoted the accumulation of phenolics. The increases in nonenzymatic antioxidants decreased O2·−, ·OH, and H2O2 contents. Conversely, 1-MCP treatment increased NADPH oxidase (NOX) activity and induced transient oxidative stress, which significantly activated enzymatic antioxidants, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), thus maintaining a lower ROS level. Treatment with both sucrose and 1-MCP exhibited a synergistic effect on alleviating oxidative stress, downregulating GbSAG101 and GbATG expression. Compared with sucrose treatment, 1-MCP treatment showed a greater inhibitory effect on ROS burst. Phenolic substance contents were similar in plants treated with sucrose and 1-MCP at the end of the storage period. Therefore, we speculated that higher levels of antioxidant enzyme activity may decrease the consumption of nonenzymatic antioxidants. Our experimental results indicated the involvement of different pathways in the effects of sucrose treatment, 1-MCP treatment, and combined treatment on delaying ROS burst, and suggested potential alternative methods for the preservation of vegetables with stems during the postharvest storage.