In vivo formation of 1-malonylaminocyclopropane-1-carboxylic acid and its relationship to ethylene production in cocklebur seed segments: A tracer study with 1-amino-2-ethylcyclopropane-1-carboxylic acid

The in vivo formation of 1-malonylaminocyclopropane-1-carboxylic acid (malonyl-ACC) and its relationship to ethylene production in the axial tissue of cocklebur (Xanthium pennsylvanicum) seeds were investigated using the stereoisomers of the 2-ethyl derivative of ACC (AEC), as tracers of ACC. Of the four AEC isomers, the (1R, 2S)-isomer was converted most effectively to a malonyl conjugate as well as to 1-butene. Malonyl-AEC, once formed, was not decomposed, supporting the view that malonyl-ACC does not liberate free ACC for ethylene production in this tissue. d-Phenylalanine inhibited the formation of malonyl-AEC and, at the same time, promoted the evolution of 1-butene, whereas l-phenylalanine did not. Possibly, the d-amino-acid-stimulated ethylene production in cocklebur seed tissues is due to an increase in the amount of ACC available for ethylene production which results from the decrease of ACC malonylation in the tissues treated with d-amino acid. 2-Aminoisobutyric acid, a competitive inhibitor of ACC-ethylene conversion, did not affect the malonylation of AEC.