Photoinduced Seed Germination of Oenothera biennis L: III. Analysis of the Postinduction Period by Means of Temperature.

The postinduction period of Oenothera biennis L. seed germination was examined by temperature treatments. For all experiments, seeds received a standard 24 hour/24 degrees C preinduction period and 12 hour/32 degrees C photoinduction period. Germination is inhibited by postinduction temperatures above 32 degrees C. When seeds are briefly incubated at 44 degrees C and then transferred to 28 degrees C, they germinate at a much lower percentage than 28 degrees C controls. When thermally inhibited seeds are placed in the dark at 28 degrees C for 20 hours, they can be promoted to germinate by a single pulse of red light. Seeds incubated at 12 degrees C or below immediately after photoinduction enter a lag period in which they germinate slowly or not at all for a long time and then resume germination. The length of the lag period is exponentially related to the postinduction temperature. When seeds are incubated at a low temperature and then transferred to a warm temperature, they germinate much more rapidly than seeds not incubated at a low temperature. A model is proposed which is consistent with these and additional results. In the model, a germination promoter is irreversibly formed from a precursor and the synthesis of the precursor is favored at low temperatures and its degradation is favored at high temperatures.