Control by Phytochrome of Glutathione Reductase Levels in the Mustard Seedling

Abstract

Abstract The time-courses of the level of glutathione reductase (GR; EC 1.6.4.2) were followed in cotyledons and hypocotyl of the developing mustard seedling in the dark and under the influence of light (phytochrome). Localization of GR on polyacrylamide disc electrophoresis columns indicate that 2 isoenzym es of GR are present in both organs under all experimental conditions. GR can be induced by light (phytochrome) in the cotyledons; however, there is no influence of light (phytochrome) on the time-course of the level of GR in the hypocotyl. While the actual lag-phase of the response in the cotyledons is less than 6 hours (onset of light at 48 hours) there is no detectable effect of light on apparent GR synthesis before approx. 42 hours after sowing. Irrespective of the onset of light (at 24 or 36 hours after sowing) the time-course of the enzyme level remains precisely the same. A red pulse given at 24 hours after sowing leads to an increase of the enzyme level as determined 60 hours later. T he effect of the red pulse is fully reversed by a far-red light pulse given at 24 hours but not 12 hours later. Facts of this kind have led to the concept of a stable inter­ mediate in the chain of regulatory events between phytochrome (P fr) and GR increase. No in d i­ cations of a coordinated, simultaneous induction by phytochrom e of GR and ascorbate oxidase (AO) could be found. This result does not support the concept that a respiratory chain exists in which AO functions as a terminal oxidase.