Effect of ethylene and 1-methylcyclopropene on chlorophyll catabolism of broccoli florets

Branchlets of broccoli ( Brassica oleracea L.) were used to examine ethylene-stimulated chlorophyll catabolism. Branchlets treated with: 1) air (CK); 2) 1 muL.L-1 1-methylcyclopropene (1-MCP) for 14 hr at 20degreesC; 3) 1000 muL.L-1 ethylene (C2H4) for 5 hr at 20degreesC; or 4) 1-MCP then C2H4, were stored in the dark at 20degreesC 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.