Action of Phytochrome During Prechilling of Amaranthus retroflexus L. Seeds.

Dark germination of Amaranthus retroflexus L. seeds at 35 degrees increased after several days of prechilling at 20 degrees or lower. Irradiation with far-red light for short periods during the early hours of a prechilling period at 10 degrees inhibited subsequent dark germination at 35 degrees . The inhibition was completely reversible with red light. Far-red irradiation in the latter part of the prechilling period was less effective. Increased dark germination of A. retroflexus seeds following a prechilling period at 20 degrees or less is attributed to action of preexistent P(FR), the far-red absorbing form of phytochrome, within the seeds. Inactivation of P(FR) was found to proceed ca. 4 times more rapidly at 25 degrees than at 20 degrees . Failure of imbibition temperatures above 20 degrees to increase dark germination of A. retroflexus seeds is attributed to the rapid thermal reversion of pre-existent P(FR). We suggest that the action of prechilling (layering) on many other seed kinds arises in a similar way.