Biochemical analysis and photosynthetic activity of chloroplasts and Photosystem II particles from a barley mutant lacking chlorophyll b

Abstract

Ultrastructural, biochemical and photochemical characteristics of chloroplasts from a natural chlorophyll b-less mutant of barley ( Hordeum vulgare L.) have been investigated by comparing them to the wild genotype. Photosystem II (PS II) particles and fractions enriched in light-harvesting chlorophyll a b- protein complex (LHC II fractions), isolated from the two genotypes, have been studied. Mutant chloroplasts were characterized by the presence of macrograna and a 2-fold lower membrane density than in wild-type chloroplasts. In mutant plastids, gel electrophoresis showed a marked decrease in the 25 and 27 kDa polypeptides linked to LHC II and in the 24 kDa polypeptide assigned to Photosystem I (PS I) antennae. The use of a non-denaturating method, including solubilization of thylakoids by digitonin followed by electrophoresis in the presence of deoxycholate, as well as the analysis of LHC II fractions, confirmed the high lability of the protein-pigment associations of the PS II antenna in the mutant. Analysis of the kinetics of fluorescence induction of plastid suspensions from the two genotypes indicated an important reduction, both in size and number, of PS II antennae in the mutant. The amount of acyl lipids was 2-fold higher in mutant chloroplasts, but only slight changes were observed in their fatty acid content. Similar photosynthetic activities were noted in chloroplasts from the two genotypes, although the ratio PS I/PS II was significantly higher in the mutant. Formation of macroganal structures in chlorophyll b-less plastids suggests a reorganization of the intraplastidial lamellar system to optimize energy distribution between the two photosystems.