1-Methylcyclopropene inhibits degreening but stimulates respiration and ethylene biosynthesis in grapefruit

We determined the effects of I-methylcyclopropene (1-MCP) and ethylene on color change and CO2 and ethylene production in grapefruit. Treatment with 1-MCP at concentrations equal to or greater than 75 nL(.)L(-1) inhibited ethylene-induced degreening, but increasing 1-MCP concentrations greater than 150 nL(.)L(-1) did not cause additional inhibition of degreening. Although ethylene-induced degreening was inhibited by 1-MCP, the effect was transient. Treating grapefruit with 15 to 75 nL(.)L(-1) 1-MCP resulted in a slight suppression Of CO2 production, whereas treatment with 150 or 300 nL(.)L(-1) 1-MCP resulted in rates Of CO2 production significantly higher than nontreated fruit. 1-MCP treatment also caused a very pronounced increase in the rate Of C2H4 production that was both dose- and time-dependent. The effects of 1-MCP on respiration and ethylene evolution were reduced if fruit was subsequently exposed to ethylene. Fruit treated with 1-MCP alone had the highest rates Of CO2 production, fruit treated with ethylene after 1-MCP or ethylene alone had intermediate rates Of CO2 production, and control fruit had the lowest rate Of CO2 production. Rates Of C2H4 evolution were approximate to 200 nL(.)kg(-1.)h(-1) from control and C2H4-treated fruit compared with approximate to 10,000 nL(.)kg(-1.)h(-1) from 1-MCP-treated fruit; fruit treated with ethylene after 1-MCP had ethylene production rates of approximate to 400 nL(.)kg(-1.)h(-1). Our results lend further support for a regulatory role for ethylene in degreening of citrus and suggest that endogenous levels of ethylene regulate ethylene production.