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

Abstract

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 generated 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 2 types of mutants were also strikingly different from one another, as were the electrophoretic patterns of the thylakoid polypeptides.