Endogenous rhythmicity and energy transduction. III. Time course of phytochrome action in adenylate kinase, NAD- and NADP-linked glyceraldehyde-3-phosphate dehydrogenase in Chenopodium rubrum

Abstract

Evidence is presented that phytochrome triggers and maintains the increase in adenylate kinase (AK) as well as NAD- and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD- and NADP-GPD) activity. After cyclic germination conditions, the time courses of all three enzymes display an endogenous rhythmic increase of their activities in constant far-red light. After germination in constant conditions, NAD- and NADP-GPD activities displayed no rhythm, while AK activity increased rhythmically. Such readiness of AK activity to oscillate was taken as indication of a close functional relationship between the control mechanism(s) of the endogenous rhythm and AK activities. The time courses in NADP-GPD activity demonstrated that phytochrome acted as an on-off switch for the increase in enzyme activity and also controlled enzyme activity depending on the relative concentration of active phytochrome. There is evidence for a function of phytochrome in the "ground state" as well as in an "activated state."It is suggested that phytochrome could be coupled to endogenous rhythmicity by modulating the redox potential of the cell, while phytochrome action itself would be timed by the endogenous rhythm.