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Composition and Function of Thylakoid Membranes from Grana-rich and Grana-deficient Chloroplast Mutants of Barley ¹

C. S. French^a

Institute of Genetics, University of Copenhagen, DK-1353 Copenhagen K, Denmark, Department of Physiology, Carlsberg Laboratory, DK-2500 Copenhagen, Valby, Denmark, ^a Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305

Chlorophyll-deficient barley (Hordeum vulgare) mutants were studied that had chlorophyll a/b ratios either higher or lower than the wild type. Mutants with high ratios (>5.2) had a reduced proportion of their photosynthetic lamellae appressed into grana ("grana-deficient" mutants) compared with wild type (chlorophyll a/b = 3.2), while the majority of lamellae in the chloroplasts with low chlorophyll a/b ratios (2.0-2.4) were organized into grana ("grana-rich" mutants).

All mutants catalyzed photosystem I and photosystem II electron transport, were tightly coupled as evidenced by increased rates of electron transport in the presence of methylamine, and were able to generate a light-dependent transmembrane proton gradient. Differences were evident in rates of electron transport per mole of chlorophyll. The mutants having high chlorophyll a/b ratios catalyzed 15- to 50-fold higher rates of ferricyanide photoreduction than the mutants having low chlorophyll a/b ratios, and 5- to 7-fold higher than the wild type.

Low temperature absorption spectra of chloroplast fragments showed that the grana-deficient mutant with a high a/b ratio had a chlorophyll spectrum characteristic of a PSI preparation while mutants with the low ratio had a spectrum typical of a PSII preparation.

The temperature fluorescence emission spectra of thylakoid membrane fragments from the two types of mutants were also strikingly different from one another, as were the electrophoretic patterns of the thylakoid polypeptides.

³ Visiting Professor, University of Copenhagen 1973-1974 and the Carlsberg Laboratory 1974-1976. Permanent address: Plant Physiology Unit, CSIRO Division of Food Research, P.O. Box 52, North Ryde, N.S.W., 2113, Sydney, Australia.

⁴ Permanent address: Department of Genetics, Royal Veterinary and Agricultural University, DK-1870 Copenhagen V, Denmark.

¹ Financial support was given by United States Public Health Service Grant GM22051 from the National Institutes of Health, and by the Danish Natural Science Research Council. CIW-DPB Publication No. 618.

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