Photosystem Damage and Spatial Architecture of Thylakoids in Chloroplasts of Pea Chlorophyll Mutants

Abstract

The effect of chlorophyll-protein complexes on the ultrastructure of chloroplasts was studied in the leaves of pea, the parent cultivar Torsdag and mutants chlorotica 2004 and 2014. The mutants were shown to accumulate 80 and 55% of chlorophyll, relative to the control, while the composition of the synthesized photosystem complexes was the same as in the parent cultivar Torsdag. The size of the light-harvesting antenna was similar to the control in the 2014 mutant but considerably increased (by 30%) in the 2004 mutant. These changes were due to a proportional decrease in the number of all complexes (by 40-45%) in the 2014 mutant. At the same time, the number of reaction center complexes of photosystem I (PS I) decreased by 50% while that of photosystem II (PS II) remained virtually constant in the 2004 mutant. A proportional decrease in the number of the PS I and PS II complexes in the chlorotica 2014 mutant was accompanied by a partial reduction of the entire chloroplast membrane system against the background of normal development of both granal and intergranal sites of thylakoids. Conversely, the loss of PS I reaction centers led mainly to the reduction of the intergranal sites of thylakoids in chloroplasts. This effect is attributed to the prevalence of PS I complexes in the intergranal thylakoids.