Effects of α‐aminoisobutyric acid and D‐ and L‐amino acids on ethylene production and content of 1‐aminocyclopropane‐1‐carboxylic acid in cotyledonary segments of cocklebur seeds

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Abstract
In the cotyuledonary tissue of cocklebur (Xanthium pennsylvanicum Wallr.) seeds, AIB (α‐ aminoisobutyric acid) inhibited not only the endogenous ethylene production but also the ACC (1‐aminocyclopropane‐1‐carboxylic acid)‐dependent and IAA‐induced ones. The inhibition of the endogenous ethylene production by AIB was accompanied by the accumulation of ACC in the tissue. Thus AIB may act as a competitive inhibitor of the conversion of ACC to ethylene and thereby inhibit ethylene production. The promotion of ethylene production by D‐isomers of some amino acids, such as phenylalanine, valine, threonine and methionine was accompained by and increse in the ACC content, the degree of which was similar to that of the stimulation of ethylene production. Moreover, these D‐amino acids stimulated the conversion of exogenously applied ACC to ethylene. The corresponding L‐isomers failed to produce these effects. It seems likely that D‐amino‐acid‐stimulated ethylene production results from the increases of both the biosynthesis and degradation of ACC. Only for tryptophan did both D‐ and L‐isomers cause an increase in ethylene production and in ACC content in the segments. The mechanism of stimulation of ethylene production by the tryptophen isomers is possibly due to their conversion to IAA in the cotyledonary tissue.