Effect of ethylene and 1-methylcyclopropene on chlorophyll catabolism of broccoli florets
2003
Gong, Y. | Mattheis, J.P.
Branchlets of broccoli (Brassica oleracea L.) were used to examine ethylene-stimulated chlorophyll catabolism. Branchlets treated with: 1) air (CK); 2) 1 microliters (.) L-1 1-methylcyclopropene (1-MCP) for 14 hr at 20 degrees C; 3) 1000 microliters (.) L-1 ethylene (C2H4) for 5 hr at 20 degrees C; or 4) 1-MCP then C2H4, were stored in the dark at 20 degrees C for up to 3 d. Chlorophyll (Chl) content and branchlet hue angle decreased during the storage period and 1-MCP treatment delayed this change. Chl degradation in broccoli was accelerated by exposure to C2H4, especially for Chl a. Prior treatment with 1-MCP prevented degreening stimulated by C2H4. Lipoxygenase activity was not altered by any of the treatments, however, 1-MCP with or without ethylene resulted in reduced activity of chlorophyllase (Chlase) and peroxidase (POD). Exposure to C2H4 stimulated Chlase activity and extended the duration of high POD activity. Treatment with 1-MCP followed by C2H4 resulted in reduced POD activity and delayed the increase in Chlase activity. The results suggest chlorophyll in broccoli can be degraded via the POD-hydrogen peroxide system. Exposure to C2H4 enhances activity of Chlase and extends the duration of high POD activity, and these responses may accelerate degreening. Treatment with 1-MCP delays yellowing of broccoli, an effect that may be due to the 1-MCP-induced reduction in POD and Chlase activities.
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