Light actions in the germination of cocklebur seeds: III. Effects of pre-treatment temperature on germination responses to far-red light and on dark germination in the red light-requiring upper seeds

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Light actions in the germination of cocklebur seeds. III. Effects of pre-treatment temperature on germination responses to far-red light and on dark germination in the red light-requiring upper seeds.-J. exp. Bot. 36: 1465-1477.Red light (R) responsiveness in R-requiring upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds changed in different patterns during a soaking period at different temperatures. At temperatures above 23°C, the responsiveness increased and then decreased. At lower temperatures (3-18°C), however, it continued to increase throughout an experimental period. The lower temperatures caused germination in the subsequent dark at 33°C, regained the R responsiveness and acquired the dark germinability when subsequently exposed to 8°C, to an extent proportional to the duration of the chilling.Far-red (FR) was inhibitory to germination in an earlier soaking period at lower temperatures, but its effect gradually decresed, and finally turned promotive. The negative FR response was repeatedly controlled by the following R irradiation. However, the positive FR response was enhanced by an immediate R irradiation, and FR/R reversibility occurred after the second FR. In contrast to the R responsiveness and dark germinability, the positive germination response to FR was not induced by soaking at 3°C, in which the growth of the axial tissue as a photoreceptive site did not occur at all. Similarly, it was not manifested when the seeds soaked at 33°C were subsequently subjected to 8°C.