Etude du phytochrome detectable,in vivo dans les graines de Cucurbita pepo L. au cours des differentes phases de la germination

Summary In dry gourd seeds all the phytochrome is in the P_fr form. The increase of phytochrome content from the beginning of hydration involves two phases, A and B, in the embryonic axis as well as in the cotyledons. Cycloheximide does not prevent the appearance of P_r during phase A. We assume that P_r is gradually released from an inactive complex. On the other hand phase B is inhibited by cycloheximide; this could mean that a de novo synthesis of P_r occurs.Some experiments indicate that the phytochrome which is localized in the embryonic axis may be involved only in the germinating process.The phytochrome which is synthesized during phase B disappears when the seeds are irradiated with red light, while the original phytochrome does not.According to our data it seems necessary to lay down a new and precise definition of the germination process.