Development of Photochemical Activity in Chloroplast Membranes. I. Studies With Mutants of Barley Grown Under a Single Environment

Abstract

The development of photochemical competence in chloroplast thylakoid membranes was studied using a series of nuclear gene mutants of barley. The chloroplasts of each mutant reached a different developmental stage when grown under a single set of environmental conditions. Photochemical capacity as well as morphological and compositional features were compared for chloroplasts in the primary leaves of eight mutants and wild-type barley (Hordeum vulgare cv. Svalöfs Bonus) after growth of the plants for 7 days at 21°C and 1700 lux. The results obtained indicated a sequence for the progressive acquisition of photochemical capability by the chloroplast membranes. The least developed of the mutant chloroplasts photoreduced ferricyanide but not 2,6-dichloroindophenol (DCIP). Immature chloroplast membrane systems from other slightly more developed mutants showed a low activity for DCIP photoreduction which was stimulated by diphenylcarbazide. In these mutants, however, the rate of photoreduction of ferricyanide was not stimulated by the uncoupler methylamine, proton pump activity was not detected and photosystem I activity was low. In the more developed of the mutant thylakoid systems, photoreductive activity was stimulated by methylamine and a proton gradient was generated in the light. The more developed the system, the greater was the stimulation obtained with methylamine. Other changes which were correlated with lamellar membrane development included a decrease in the light intensity required to saturate ferricyanide and DCIP photoreductive activities and an increase in the degree of inhibition of the photoreduction of ferricyanide by the photosystem II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). The activity changes were not correlated with either the amount of grana present or the ratio of chlorophyll a to b. Mutants showing low rates of DCMU-sensitive photoreduction of ferricyanide and DCIP were aberrant in protein composition of the chloroplast membranes.