Submitted to: Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2002
Publication Date: 1/1/2003
Citation: GONG,Y., MATTHEIS,J.P., EFFECTS OF ETHYLENE AND 1-METHYLCYCLOPROPENE ON CHLOROPHYLL CATABOLISM IN BROCCOLI FLORETS, PLANT GROWTH REGULATION, 40:33-38. 2003.
Interpretive Summary: The primary factor limiting postharvest life of harvested broccoli is loss of green color. The degreening process is stimulated by ethylene, a colorless, odorless gas emitted by plant tissue. Reducing broccoli ethylene production (via refrigeration) or exposure to ambient sources of ethylene (i.e. exhaust gases from internal combustion engines, other fresh fruit or vegetables) significantly lowers the rate of degreening. Treatment with ethylene action inhibitor 1-methylcyclopropene also reduces degreening even in presence of ethylene. Metabolic processes that degrade chlorophyll pigments constitute the mechanism of degreening. Stimulating or inhibiting these degradative activities with ethylene or 1-MCP allowed the process of chlorophyll metabolism in broccoli to be investigated and provided insight into specific metabolic events necessary for degreening to occur.
Technical Abstract: Branchlets of broccoli (Brassica oleracea L.) were used to examine ethylene-stimulated chlorophyll catabolism. Branchlets treated with: 1) air (CK); 2) 1 uL.L**1 1-methylcyclopropene (1-MCP) for 14 hr at 20 deg C;3) 1000 uL.L**1 ethylene (C2H4) for 5 hr at 20 deg C; or 4) 1-MCP then C2H4 were stored in the dark at 20 deg C for up to 3 days. Hue angle decreased during the storage period and 1-MCP treatment delayed this change. Broccoli degreening was accelerated by exposure to C2H4, however, 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. The 1-MCP + C2H4 treatment 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 contribute to accelerated 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.