Photosynthetic Performance of Cyanelles in the Endocyanomes Cyanophora, Glaucosphaera, Gloeochaete, and Glaucocystis

Abstract

Summary The photosynthetic performance of the blue-green endosymbiotes (cyanelles) in four apoplastidal algae, Cyanophora paradoxa, Gloeocbaete wittrockiana, Glaucosphaera vacuolata, and Glaucocystis nostochinearum , has comparatively been investigated. All cyanelles exhibit rates of light dependent carbon assimilation comparable to other algal species. Dark carbon fixation is negligibly low. Kinetics of 14 C-labelling of intermediary photosynthates indicate that the reductive pentose phosphate cycle is operational in all cyanelles. The pattern of 14 C-labelled low-molecular weight photosynthetic products is very similar in all endocyanomes investigated. It differs considerably from 14 C-assimilate patterns of the Rhodophyta (and Chlorophyta). Sucrose is not 14C-labelled in the cyanomes, whereas glucose, maltose, and fructose are the most intensely labelled compounds encountered. The comparison of the intact association Cyanophora paradoxa and its isolated cyanelles as well as the results from feeding experiments with 14 C-glucose suggest that glucose is transferred from the cyanelles to the host cells and there converted into disaccharides (maltose) and/or polyglucans. The results are discussed with emphasis on the symbiotic status of the cyanelles.