Changes in Ethylene Production and in 1-Aminocyclopropane-1-carboxylic Acid (ACC) and Malonyl-ACC Contents of Cocklebur Seeds during Their Development

Ethylene production in developing cocklebur (Xanthium pennsyluanicumWallr.) seeds peaked when the dry weight of the seeds beganto increase in the early period of development. The productionthen began to decrease and stopped when the dry weight increasewas completed. The upsurge of ethylene production in the earlydevelopmental period paralleled increases in ACC synthase activityand the 1-aminocyclopropane-1-carboxylic acid (ACC) contentof the seeds, both of which rapidly decreased later. Malonyl-ACC (MACC) accumulated in developing cocklebur seedsduring the early period of development, before the ACC contentand ethylene production increased. Although the ACC synthaseactivity, ACC content and ethylene production showed markeddecreases, the MACC content remained almost unchanged duringthe middle period of seed development, with a pronounced decreaseoccurring in the late period. Exogenous application of MACCdid not promote ethylene production of seeds collected at thelate developmental stage. Aminoethoxyvinylglycine, an inhibitorof ACC synthase, strongly inhibited the ethylene productionof the same lot of seeds. Therefore, the decrease in the MACCcontent in developing cocklebur seeds was not due to reuse ofMACC for ethylene production. (Received May 24, 1984; Accepted August 15, 1984)