Thermoperiodism Mechanism in the Germination of Cocklebur Seeds

In thermoperiodic germination of secondarily dormant cocklebur(Xanthium pennsylvanicum Wallr.) seeds, the extent of electronflow through the CN-sensitive, cytochrome path and the CN-resistant,alternative path differred in the cool and warm phases. Thecool phase triggered active engagement of the alternative pathduring the subsequent warm phase, and this led to an increasein the ratio of the alternative path flux to the cytochromepath flux. The cool and warm phases had different functionsin adenylate metabolism. The former acted mainly in the productionand accumulation of ATP, whereas the latter supplied ADP and,especially, AMP. Thus an increasing number of sequential thermoperiodiccycles augmented the size of the adenylate pool and the energycharge, both of which may be necessary for germination to takeplace. (Received September 16, 1981; Accepted November 5, 1982)