Postharvest application of 1-methylcyclopropene delays chloroplast degradation in Gynura bicolor DC under sugar scarcity conditions

During postharvest transport and storage stage,Gynura bicolor DC (G. bicolor) is commonly handled in the darkness. However, long-term storage in the dark exacerbates postharvest sugar scarcity. 1-methylcyclopropene (1-MCP) was showing effective in inhibiting postharvest physiological metabolism of fruits and vegetables. The aim of this research was to uncover the mechanism underlying the effects of 1-MCP on the chloroplasts of G. bicolor under postharvest sugar scarcity conditions. The status of carbon sources, the enzymes and genes involved in chloroplast degradation were investigated. Furthermore, reactive oxygen species (ROS), chloroplast function, and chloroplast structure were also investigated to examine the physiological changes that occur in chloroplasts during storage. Degradations of starch, soluble sugar, and soluble protein were effectively retarded by 1-MCP. The increase of free amino acid content and decay rate were markedly inhibited by 1-MCP. 1-MCP not only inhibited the ROS burst, structural disintegration, and function (maximum photochemical efficiency Fv/Fm, effective quantum yield of PSII photochemistry QY, and relative electron transfer rate ETR) decreased in chloroplast, but also delayed the increased activities of chlorophyll degraded-related enzymes (chlorophyllase CHL, pheophytin pheophorbide hydrolase PPH and Mg-dechelatase), and proteinases (cysteine proteinase CP, serine proteinase SP and total proteinases TP), which retarding the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), and chlorophyll degradation. The upregulated expressions of GbCHL, GbPPH, Gb-proteinases, GbATGs, and GbSAG101 were markedly blocked by 1-MCP. Correlation analysis showed that ROS burst was associated with sugar scarcity, the upregulated expressions of GbATGs, and GbSAG101 were associated with sugar scarcity and ROS burst, chlorophyll degradation was associated with the RuBisCo level. In conclusion, 1-MCP effectively delayed chloroplast degradation in G. bicolor by retarding sugar scarcity, inhibiting ROS burst in chloroplast, blocking the upregulated expressions of genes involved chloroplast degradation, and delaying the activities increase in proteases and chlorophyll degraded-related enzymes.