Photosynthetic Ability of Radish Cotyledons Grown under Continuous Standard Far-Red Light: Photo-activation of NADP(H) Glyceraldehyde-3-Phosphate Dehydrogenase

Abstract

An investigation of the photosynthetic competence of radish cotyledons grown under continuous standard far-red light is reported, following the study of photo-activation of NADP(H) glyceraldehyde-3-phosphate dehydrogenase. The in vitro illumination of isolated organelles using white light resulted in a 1-85-fold enhancement of enzymatic activity. This increase was dependent upon the age of the seedlings and could only be observed when organelles were extracted from far-red- or daylight-grown plants and when their structure was kept intact. Photosynthetic electron flow was involved in the modulation of the activity, as shown by the use of specific inhibitors. A dark deactivation of the enzymatic activity was also observed, leading to the conclusion that the activating regulatory process, likely to be related to ferredoxin/thioredoxin, is present in vivo under standard far-red light.