Identifying Flavor Metabolites Under Ethylene Regulation in Apples

Abstract

To understand the role of ethylene in overall flavor of apple fruits, ethylene production, and action were reduced using apple trees lines transformed for suppressing activity of ACC-synthase or ACC-oxidase enzymes, and 1-methylcyclopropene (1-MCP), an ethylene action inhibitor. A major reduction in ethylene biosynthesis and respiration rates was measured in fruits from these treatments. As expected, we found differential levels of dependence of flavor components on ethylene biosynthesis and action. Regarding aroma production, an ethyleneassociated event, headspace analysis showed a reduction in ester production in the ethylene-suppressed lines and in the apples treated with 1.0 μL·L-1 1-MCP for 20 hours at 20 °C. However, no major differences were observed in concentrations of alcohol and aldehyde volatiles. Other flavor metabolites that showed an ethylene-dependent pattern were organic acids and sugars. Malic acid degradation was significantly reduced under ethylene suppressed conditions, showing a recovery after exposing the fruit to ethylene. Sucrose and fructose concentrations were influenced by suppression or enhancement of ethylene. Total phenolics and individual phenolics showed an ethylene-dependent behavior only when ethylene biosynthesis was reduced, but not when ethylene action was affected. These results suggest that the regulatory mechanisms of aroma biosynthesis in apple are under partial ethylene regulation. Therefore, we are using the ethylene suppressed apple fruits study the channeling and regulation of other metabolic pathways that lead to the manifestation of a complex trait like fruit quality.