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Photosystem II Activity, Plastoquinone A Levels, and Fluorescence Characterization of a Virescens Mutant of Barley ¹

Department of Plant Sciences, University of Alberta, Edmonton, Alberta T6G 2E3 Canada

Chloroplasts isolated from seedlings of a virescens mutant of barley (Hordeum vulgare L cv Gateway) grown for 6 days under continuous illumination had lower levels of photosystem II activities on a chlorophyll basis than wild-type seedlings. After 8 days, however, the photosystem II rates of the mutant and wild-type were approximately equal. Lower levels of the photosystem II activities in the mutant were correlated with a smaller functional plastoquinone pool size as determined by room temperature fluorescence induction. Higher levels of extractable plastoquinone A on a chlorophyll basis, however, were obtained from mutant chloroplasts. An increased room temperature fluorescence yield in the mutant was shown to be due to a higher level of initial fluorescence. A decreased sigmoidicity in the room temperature fluorescence induction transient in the presence of diuron and an increased 77 K fluorescence emission at 680 nanometers lead us to believe that a certain population of the light harvesting chlorophyll protein complex in the mutant membranes is unconnected to photo-system II reaction centers. Although photochemical activities of the mutant approach wild-type values as the mutant develops, the population of dissociated light harvesting complexes does not appear to change.

¹ Supported partially by a Natural Sciences and Engineering Research Council of Canada grant to S. Z. and United States Department of Energy contract No. DE-AC02-76ER0-1338. D. J. K. is recipient of a Natural Sciences and Engineering Research Council Post Graduate Scholarship.