Volatile biosynthesis during ripening of 'Jonagold' apple fruit: Association of gene expression with aroma volatiles.

摘要

Changes in the volatiles produced by 'Jonagold' apple (Malus x domestica Borkh) during ripening and senescence were related to changes in gene expression using a cDNA-based microarray containing over 10,000 gene fragments. Patterns for aroma biosynthesis, internal ethylene content, respiration, skin color, starch, and texture were typical for climacteric fruit. Volatile compounds and CO2 increased after a rapid increase in ethylene production. Straight-chain esters hexyl acetate and butyl acetate and branched-chain esters 2-methylbutyl acetate and hexyl 2-methylbutanoate were found to be the major esters detected by GC/MS. Long chain esters predominated during the early stages of ripening and short chain esters increased later in proportion. Generally, the alcohols increased at an earlier development stage than the esters for which they acted as substrates. Esters are formed by combining alcohol with CoA derivative of fatty acid by the action of alcohol acyltransferase (AAT). Patterns in gene expression reflecting the rise and fall in ester formation were found in some putative genes for amino acid metabolism (branched-chain aminotransferase and branched-chain alpha-keto acid decarboxylase), fatty acid metabolism, and ester formation. The pathway for branched-chain ester biosynthesis is discussed.