Freeze fracture study of thylakoid organization of Cryptomonas rufescens (Cryptophyceae) according to illumination conditions

Abstract

Freeze fracture of pair-associated thylakoids of Cryptomonas rufescens control and high illuminated cells exhibits four types of surfaces. The thylakoid particle densities of control cells are analogous to those of higher plants and Chlorophyceae, but their sizes are smaller than those described for higher plants and other Cryptophyceae. The high light intensity induces changes in the densities and the sizes of the particles, which can be correlated with a decrease in the amount of phycoerythrin and chlorophylls associated with PS II. However, the functional organization of the remaining PS II antennae tested by fluorescence characteristics, is kept. These data allow to consider the significance of the membrane particles and suggest a partial segregation of the two photosystems. We conclude that PS II and its two light-harvesting antennae (phycoerythrin and chlorophyll a/c antenna) would be mainly in the stacked parts of the thylakoids, while unstacked parts would contain PS I and phycoerythrin associated with PS II centers.