Effect of aminocyclopropane-1-carboxylic acid oxidase antisense gene on the formation of volatile esters in cantaloupe charentais melon (Cv. Vedrandais)

The role of ethylene on volatile formation associated with ripening was investigated on melon hybrids transformed with an aminocyclopropane-l-carboxylic acid oxidase antisense gene. The headspace of four antisense hybrid fruits was analyzed by GC/MS and compared to that of nontransformed hybrid fruit. The major volatiles extracted from nontransformed hybrids were esters, mostly acetates. However, the most potent odorants were ethyl esters, such as ethyl butanoate, and branched-chain esters, such as ethyl 2-methylpropanoate and ethyl 2-methylbutanoate. In antisense hybrids, the total volatiles were 60-85% lower than that of the nontransformed hybrids. Volatiles with low odor values, such as ethyl, 2-methylpropyl and 2-methylbutyl acetates, were half to a fifth lower than in nontransformed hybrids, whereas potent odorants, such as ethyl 2-methylpropanoate and ethyl 2-methylbutanoate, were <3% that of nontransformed hybrids. Examination of the biosynthetic pathways of volatile esters derived from amino acids demonstrates that ethylene stimulated preferentially the synthesis of the most potent odorants.