Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2006
Publication Date: February 1, 2007
Citation: McCollum, T.G., Maul, D.P. 2007. 1-Methylcyclopropene inhibits degreening but stimulates respiration and ethylene biosynthesis in grapefruit. HortScience. 42(1):120-124.
Interpretive Summary: Ethylene is a gaseous plant hormone that affects many aspects of plant growth and development. The role of ethylene in ripening of climacteric fruit (e.g., tomatoes, bananas, apples, avocados) has received considerable study and its role understood. In contrast in non-climacteric fruit (e.g., grapes, strawberries, citrus) little is known about the role of ethylene. Citrus fruit do produce ethylene and ethylene is used commercially to 'degreen' the fruit; however, our understanding of the role of ethylene in citrus fruit development is limited. Our objective in these experiments was to define more clearly the effects of ethylene in citrus fruit. We treated grapefruit with 1-methylcyclopropene (1-MCP) a compound that inhibits the perception of ethylene, and thereby blocks ethylene action, in order to gain insight regarding the role of ethylene. We determined the effects of 1-MCP at different doses and also the effect of 1-MCP alone or in combination with ethylene. We found that 1-MCP has very pronounced effects on grapefruit. Ethylene-induced degreening was inhibited by 1-MCP. However, 1-MCP treatment caused an increase in the production of carbon dioxide and ethylene, suggesting that perception of ethylene may affect respiration and is required to regulate production of ethylene by grapefruit. Understanding the role of ethylene in citrus fruit has both fundamental and economic importance. Ethylene is used commercially, but can lead to increased losses due to decay. Developing a better understanding of the role of ethylene in citrus fruit physiology will allow for the development of treatments to reduce postharvest losses of fresh citrus fruit.
We determined the effects of 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 inhibited ethylene-induced degreening, but increasing 1-MCP concentrations greater than 150 nL/L did not cause additional inhibition of degreening. Although ethylene-induced degreening was inhibited by 1-MCP, the effect was transient. Treating grapefruit with 15 ' 75 nL/L 1-MCP resulted in a slight suppression of CO2 production whereas treatment with 150 or 300 nL/L 1-MCP resulted in rates of CO2 production significantly higher than non-treated fruit. 1-MCP treatment also caused a very pronounced increase in the rate of C2H4 production that was dose and time dependent. The effects of 1-MCP on respiration and ethylene evolution were significantly reduced if fruit were subsequently exposed to ethylene. Fruit treated with
1-MCP alone had the highest rates of CO2 production, fruit treated with 1-MCP + ethylene or ethylene alone had intermediate rates of CO2 production and control fruit had the lowest rate of ethylene evolution. Rates of C2H4 evolution were ca. 200 nL/kg h-1 from control and C2H4-treated fruit compared to ca.10,000 nl/kg h-1 from 1-MCP treated fruit; fruit treated with ethylene following 1-MCP had ethylene production rates of about 400 nL/kg 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.