HETEROGENEITY OF MITOCHONDRIAL PROTEIN BIOGENESIS DURING PRIMARY LEAFDEVELOPMENT IN BARLEY

The natural developmental gradient of light-grown primary leaves of ba rley (Hordeum vulgare L..) was used to analyze the biogenesis of mitoc hondrial proteins in relation to the age and physiological changes wit hin the leaf. The data indicate that the protein composition of mitoch ondria changes markedly during leaf development. Three distinct patter ns of protein development were noted: group A proteins, consisting of the E1 beta-subunit of the pyruvate dehydrogenase complex, ORF156, ORF 577, alternative oxidase, RPS12, cytochrome oxidase subunits II and II I, malic enzyme, and the alpha- and beta-subunits of F-1-ATPase; group B proteins, consisting of the E1 alpha-subunit of the pyruvate dehydr ogenase complex, isocitrate dehydrogenase, HSP70A, cpn60C, and cpn60B; and group C proteins, consisting of the four subunits of the glycine decarhoxylase complex (P, H, T, and L proteins), fumarase, and formate dehydrogenase. All of the proteins increased in concentration from th e basal meristem to the end of the elongation zone (20.0 mm from the l eaf base), whereupon group A proteins decreased, group B proteins incr eased to a maximum at 50 mm from the leaf base, and group C proteins i ncreased to a maximum at the leaf tip. This study provides evidence of a marked heterogeneity of mitochondrial protein composition, reflecti ng a changing function as leaf cells develop photosynthetic and photor espiratory capacity.