Ethylene Biosynthetic Responses of Mango (Mangifera indica L. cv. ‘Carabao’) Fruits to 1-methylcyclopropene (1-MCP) Preharvest Aqueous Spray Applications

800x600 The ethylene antagonist 1-methylcyclopropene (1-MCP) was used as a tool to investigate the mechanism of ethylene feedback regulation in mango (Mangifera indica L. cv. ‘Carabao’) fruits. The ethylene biosynthetic responses of mango fruits to 1-MCP applied prior the upsurge in ethylene production on-tree which was around 100 days after flower induction (DAFI) were studied. Aqueous 1-MCP spray formulation with 10 ppm concentration was applied to on-tree mango fruits at 100 DAFI. From these sprayed fruits, four (4) sets of fruits were tagged for a second round of 10 ppm aqueous 1-MCP spraying. One set was sprayed the second time at 105 DAFI, while the remaining sets at 110, 115 and 120 DAFI respectively. The positive control was sprayed with 0 ppm 1-MCP while the negative controls were the unsprayed fruits. Representative fruit samples from each set were harvested 2 d after spraying and every 2 d thereafter until reaching 120 DAFI. Right after each harvest, samples were analyzed for internal ethylene, ethylene production, ACC levels and ACC oxidase activities. The negative control exhibited two internal ethylene peaks before harvest maturity. However, in 1-MCP treated fruits, low levels of ethylene were detected and the second peak was not observed. A single application of 1-MCP at 100 DAFI resulted in lower ethylene production compared with controls. However, a second application proved to be more effective as the lowering of ethylene production was carried over until the day of harvest. The levels of 1-aminocyclopropane-1-carboxylate (ACC) increased after 110 DAFI for the controls. Reapplication of 1-MCP at 110 DAFI resulted to lower ACC levels, which was not observed with the other treatments with 1-MCP reapplication. Possibly, new ethylene receptors are synthesized at 110 DAFI, and 1-MCP reapplication at this time effectively blocks ethylene binding to the new receptors. ACC oxidase activity was lowered by 1-MCP applied at 100 DAFI compared with the controls. However, trends in ACC oxidase activities were almost the same for all the treatments and controls after 105 DAFI.  Thus, ACC oxidase proceeds with its normal activity without being inhibited by 1-MCP. This suggests that ethylene biosynthesis in ‘Carabao’ mango fruit is regulated at the level of ACC synthase and not ACC oxidase. Thus, autocatalytic ethylene biosynthesis in ‘Carabao’ mango can be controlled by regulating ACC synthase activity, which proves that ACC synthesis is the rate limiting step in ethylene feedback mechanism in ‘Carabao’ mango. Normal 0 false false false EN-PH X-NONE X-NONE