FUNCTIONAL-ORGANIZATION OF THYLAKOID MEMBRANES IN VIABLE PEA MUTANTS WITH LOW CHLOROPHYLL CONTENT

The functional organizations of thylakoid membranes from wild type pea (Pisum sativum L. cv. Kapital) and two viable mutants with low chloro phyll (Chl) contents were compared. Nuclear mutations in mutants 7 and 42 led to two- and three-fold decrease in total chlorophyll content, respectively. In spite of low Chl content mutants showed 80% photosynt hetic activity, biological productivity, and seed production. It has b een shown that mutant membranes differed from that of wild type by Chl distribution between the pigment-protein complexes and by stoichiomet ry of the main electron-transport complexes. The ratio photosystem I ( PSI):photosystem II (PSII):cytochrome (Cyt) bdf complex:Chl was 1:1.1: 1.2:650 in wild type chloroplasts, 1:1.8:1.7:600 in mutant 7, and 1:1. 5:1.9:350 in mutant 42. PSI- and PSII-dependent electron-transport act ivities were enhanced in the mutants per mg Chl in proportion to numbe r of reaction centers. The activity of the non-cyclic electron-transpo rt chain increased in proportion to PSII and Cyt b(6)/f complexes. The amount of ATP synthetase per unit of Chl as estimated by H+-ATPase ac tivity was much greater in mutant thylakoids, which is favorable for p hotosynthetic energy transduction The low content of the light-harvest ing complexes (LHC) in mutants is compensated by an increase of the nu mber of PSII and Cyt b(6)/f complexes, which eliminates the bottleneck at the site of plastoquinone oxidation.