Phytochrome Distribution in Johnsongrass Rhizomes

Phytochrome was assayed in vivo in the rhizomes of 12 to 14-week old johnsongrass [Sorghum halapense(L.) Pers.] plants. The phytochrome levels decreased basipetally from the apex through the eighth node. The decrease was logarithmic on a dry weight basis, but less rapid on a per segment basis. On a dry weight basis, higher phytochrome measurements were obtained with samples from the interior of the rhizome than from the external regions. The far-red absorbing form of phytochrome (Pfr) was shown to be very labile at 25 C in johnsongrass rhizomes. These results provide a basis for examining photomorphogenic responses of rhizomes to light and for correlating these responses to phytochrome photophysiology.