Abstract

During the imbibition of water, the change in the ethylene production of axial segments of nondormant (ND) cocklebur (Xanthium pennsylvanicum Wallr.) seeds paralleled the change in the content of free 1-aminocyclopropane-l-carboxylic acid (ACC), but not the change in conjugated hydrolysable ACC in the axes. Aminoethoxyvinylglycine, anoxia and a-aminoisobutyric acid inhibited ethylene production, the lattertwo compounds causing the accumulation of free ACC. Administration of ACC greatly enhanced ethylene production in the axes. Thus, free ACC seems to be a direct precursor of ethylene production in the axial tissue of cocklebur seeds.

Imbibed dormant (D) axes characterized by inferior ethylene production had less ability to convert exogenously applied ACC to ethylene as compared to ND axes. But, there was little difference between the D and ND axes in the endogenous contents of free and conjugated ACC. This suggests that the inferior ethylene production found in detached D axes is associated with the low activity of an ACC-ethylene converting system.

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