THE PHOTOMORPHOGENETIC CONTROL OF THE DEVELOPMENT OF PLASTID GLYCERALDEHYDE-PHOSPHATE DEHYDROGENASE AND PHOSPHORIBULOKINASE ACTIVITIES IN COTYLEDONS OF MUSTARD SEEDLINGS

The plastid glyceraldehyde-phosphate dehydrogenase and phosphoribulokinase of mustard cotyledon extracts were activated by preincubation with ATP and with ATP and dithiothreitol respectively. By in vitro activation prior to assay, it was possible to determine the potential activities, which appear to have been directly proportional to the amount of each enzyme protein present. In this way it was possible to deduce the net synthesis of these two enzymes. The induction of synthesis of glyceraldehyde-phosphate dehydrogenase and phosphoribulokinase, by continuous far red or white light were similar hut net synthesis in continuous far red continued longer for glyceraldehyde-phosphate dehydrogenase than for phosphoribulokinase. The kinetics of the development of the glyceraldehyde-phosphate dehydrogenase potential activity were very close to those reported by Bruning et al. (1975) for this enzyme. The data do not permit elimination of either the single switch or multiple switches hypotheses for the action of phytochrome. Continuous white illumination gave results similar to those for continous far red for the net synthesis of the two enzymes but it was more effective than far-red in bringing about enzyme activation in vivo.