Ethylene Production, 1-Aminocyclopropane-l-Carboxylic Acid Content and Its Conversion to Ethylene in Axial Segments of Dormant and Nondormant Cocklebur Seeds

During the imbibition of water, the change in the ethylene productionof axial segments of nondormant (ND) cocklebur (Xanthium pennsylvanicumWallr.) seeds paralleled the change in the content of free 1-aminocyclopropane-l-carboxylicacid (ACC), but not the change in conjugated hydrolysable ACCin the axes. Aminoethoxyvinylglycine, anoxia and a-aminoisobutyricacid inhibited ethylene production, the lattertwo compoundscausing the accumulation of free ACC. Administration of ACCgreatly enhanced ethylene production in the axes. Thus, freeACC seems to be a direct precursor of ethylene production inthe axial tissue of cocklebur seeds. Imbibed dormant (D) axes characterized by inferior ethyleneproduction had less ability to convert exogenously applied ACCto ethylene as compared to ND axes. But, there was little differencebetween the D and ND axes in the endogenous contents of freeand conjugated ACC. This suggests that the inferior ethyleneproduction found in detached D axes is associated with the lowactivity of an ACC-ethylene converting system. (Received December 17, 1982; Accepted April 30, 1983)