Ethylene induction of chlorophyll degradation in melinjo (Gnetum gnemon L.) leaves: Lack of correlation with chlorophyllase, chlorophyll peroxidase and chlorophyll oxidase activities

Abstract

Melinjo (Gnetum gnemon L.), a leafy vegetable native to Southeast Asia, maintains a long shelf life when sprayed with water and stored in polyethylene bags. Also, during senescence of melinjo, the onset of leaf yellowing occurs much later than that of other vegetables. Postharvest crop management of green leafy vegetables could benefit from a better understanding of the factors that affect leaf yellowing in melinjo. This study investigated changes in chlorophyll concentrations and the roles of chlorophyll-degrading enzymes in melinjo leaf yellowing under exogenous ethylene and 1-methylcyclopropene (1-MCP) treatment. We recorded shelf life, total chlorophyll, chlorophyll a and b contents, activities of chlorophyllase, chlorophyll peroxidase and chlorophyll oxidase and found no significant difference between treated and untreated leaves. Untreated leaves turned yellow after 35 d. Leaves became yellow within 2 d of the ethylene treatment, whereby the chlorophyll concentrations decreased dramatically. Previous research suggested an alternative (oxidative) pathway of chlorophyll degradation involving chlorophyll peroxidase and chlorophyll oxidase in other green vegetables. Our results indicated that chlorophyll degradation involves enzymes other than the ones measured and that the pathway of chlorophyll degradation by oxidizing activities (peroxidase and oxidase) does not take place in harvested melinjo leaves.