Ethylene Promotes the Capability To Malonylate 1-Aminocyclopropane-1-carboxylic Acid and d-Amino Acids in Preclimacteric Tomato Fruits

When whole unripe green tomato fruits (Lycopersicon esculentum Mill, cv T₃) were treated with ethylene (10 microliters per liter) for 18 hours, the fruit's ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to N-malonyl-ACC (MACC) increased markedly and such an effect was also observed in fruits of mutant nor, which cannot ripen normally. The promotion of the capability to malonylate ACC by ethylene increased with the increasing ethylene concentration from 0.1 to 100 microliters per liter and with increasing duration of ethylene treatment up to 8 hours; a longer duration of ethylene treatment did not further increase the malonylation capability. When ethylene was withdrawn, the promotion disappeared within 72 hours. Norbornadiene, a competitive inhibitor of ethylene action, effectively eliminated the promotive effect of ethylene. Ethylene treatment also promoted the fruits' capability to conjugate d-amino acids and α-amino-isobutyric acid. Since the increase in the tissue's capability to malonylate ACC was accompanied by an increase in the extractable activity of ACC and d-amino acid malonyltransferase, ethylene is thought to promote the development of ACC/d-amino acid malonyltransferase in unripe tomato fruits.