Comparison between thylakoid composition and chloroplast ultrastructure in developing plants ofBrassica, Helianthus, Sisymbrium, andTanacetum

Abstract

The relationship between the chloroplast ultrastructure and the thylakoid membrane composition was observed during the growth ofBrassica rapa ssp.oleifera, Helianthus annuus, Sisymbrium altissimum, andTanacetum vulgare. The ultrastructural measurements were made on sections cut perpendicular to the grana. In all the species the young leaves had a low proportion of P₇₀₀ chlorophyll a-protein complex (CPI in photosystem I), whereas the proportion of chlorophyll a-protein complex of photosystem II (CPa) was fairly high. The amount of chlorophyll a-protein complex of photosystem II (CPa) decreased with age, whereas the amount of P₇₀₀ chlorophyll a-protein (CPI) complexes increased. The proportion of the light-harvesting chlorophyll a/b-protein (LHCP) complexes first increased and the declined as the plants aged. The chloroplast area in longitudinal sections was highest when the total content of light-harvesting chlorophyll a/b-protein (LHCP) was high and the values declined in older plants. During ageing, the ultrastructure of the chloroplast showed increase in the size of the grana and distinct profiles of stroma thylakoids extending between large grana. The granal stacks were largest, when the proportion of P₇₀₀ chlorophyll a-protein (CPI) was high and the total amount of light-harvesting chlorophyll a/b-protein (LHCP) low. When light is not limiting, the stage of development of the plant seems to have a significant effect on the thylakoid components and thylakoid ultrastructure.