α‐Aminoisabutyric acid, propyl gallate and cobalt ion and the mode of inhibition of ethylene production by cotyledonary segments of cocklebur seeds

Using cotyledonary segments of cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the inhibitory effect of α‐aminoisobutyric acid (AIB) on ethylene production was compared with that of propyl gallate and CoCl2. Of these inhibitors only AIB was effective in causing the accumulation of endogenous free 1‐aminocyclopropane‐l‐carboxylic acid (ACC) in the tissue. The degree of inhibition of ethylene production by AIB decreased markedly with increasing concentrations of pre‐loaded ACC, while the inhibition by propyl gallate and CoCl2 changed little. Kinetic analysis showed that AIB competitively inhibited the conversion of pre‐loaded ACC to ethylene, but propyl gallate and CoCl2 did not. Short‐chain organic acids and analogues of AIB, such as acetic, propionic, butyric and cyclopropanecarboxylic acids, did not inhibit ethylene production by the segments. Thus, additional support for the competitive mode of inhibitory action of AIB on the conversion of free ACC to ethylene was provided. A conjugated hydrolysable ACC was found to be present in abundance in cotyledons of this seed. However, its content in the tissue was hardly affected by treatment with the three inhibitors and by administration of exogenous ACC, suggesting that the conjugated ACC was not directly involved in ethylene production.