POSSIBLE INVOLVEMENT OF VOLATILE COMPOUNDS IN THE AFTER-RIPENING OF COCKLEBUR SEEDS

The mechanism of emergence from primary dormancy, the process of after -ripening, in cocklebur (Xanthium pennsylvanicum) seeds was examined i n relation to the involvement of volatile compounds and to the relativ e humidity (RH) in which the seeds were stored. The after-ripening of these seeds proceeds only at water contents between 7 and 14%, which a re conditioned under RHs of 33% to 53% and are identified with water-b inding region II. After-ripening of cocklebur seeds occurred even in w ater-binding region I, imposed by 12% RH, when exposed to HCN gas duri ng the storage period. Exposure of dormant seeds to acetaldehyde (etha nal) retarded after-ripening, even in water-binding region II, thus de creasing germinability. This decrease of germinability by ethanal was found also in the after-ripened seeds, suggesting that ethanal acceler ates seed deterioration rather than retarding the after-ripening. The contents of ethanal, ethanol and HCN were high only in the dormant see ds held at 12% RH. Regardless of RH, a possible conversion of ethanal to ethanol, perhaps via alcohol dehydrogenase, was far larger in dorma nt than in non-dormant seeds. In contrast. the reverse conversion of e thanol to ethanal was more profound in non-dormant seeds, Pre-exposure of both types of seeds to HCN reduced the contents of both ethanal an d ethanol at 12% RH. The contents of various adenylates including ATP in seed tissues were higher in dormant seeds stored at 12% RH than in non-dormant seeds after-ripened at 44% RH. It is suggested that emerge nce of cocklebur seeds from primary dormancy by HCN treatment at 12% R H may result from the reduction in the contents of ethanal via an unkn own mechanism incurring the consumption of ATP. This implies involveme nt of volatile compound metabolism at the water-binding region II in t he after-ripening process of cocklebur seeds.