The light promoted germination of the seeds of Chenopodium album L. V. Dark reactions regulating quantity and rate of the response to red light

In Chenopodium album seeds the influence of the dark incubation time before a red irradiation on the subsequent germination processes was studied. During dark incubation at least two preparative reactions take place. The first one, a rehydratation of the phytochrome pigment, is both at 23 °C and 4 °C a function of the water uptake of the seeds. It regulates the rate of increase in reactivity of the seeds to red light, as measured by the final germination percentage. In the second one a reaction component for the far-red absorbing form of phytochrome (Pfr) is synthesized. This synthesis does not occur at 4°C. The amount of this component synthesized before onset of a red irradiation, determines the reaction rate of Pfr and consequently the escape from the antagonistic effect of a far-red irradiation, which in turn determines the moment of visible germination. The processes between the moment of escape and the moment of the protrusion of the rootlet through the inner seed-coat layer are not influenced. The lower final germination percentage, after a 4°C pre-treatment, as compared with incubation at 23 °C, is supposed to be caused by the dark conversion of Pfr to Pr in the absence, at the lower temperature, of the product of the second reaction.