Daminozide inhibits ethylene production in apple fruit by blocking the conversion of methionine to aminocyclopropane-1-carboxylic acid (ACC)

Abstract

At harvest, fruit from apple trees sprayed with daminozide (+daminozide) had lower levels of aminocyclopropane-1-carboxylic acid (ACC) and produced significantly lower amounts of ethylene than untreated (−daminozide) fruit. Flesh discs from the fruit of +daminozide and −daminozide trees were fed precursors of ethylene to determine how daminozide inhibits ethylene production. ACC was metabolized to ethylene regardless of treatment. Methionine (MET), however, was only converted to ethylene by −daminozide fruit, and only after the fruit had been maintained at 4 °C for 5 months. +Daminozide fruit failed to convert MET to ethylene at harvest, as well as after cold storage. When daminozide was added to the incubation media of flesh discs it did not inhibit ethylene production or the conversion of ACC to ethylene. The addition of daminozide did, however, inhibit the metabolism of exogenous MET to ethylene. Aminooxyacetate acid (AOA) blocked both the endogenous production of ethylene and that from MET feeds. Daminozide inhibits ethylene production by preventing the conversion of MET to ACC, but it does not appear to act as a simple competitive inhibitor of ACC synthase activity.