Exchange of Metabolites in Cyanophora paradoxa and its Cyanelles*

Abstract

The flagellate Cyanophora paradoxa contains blue-greenish, organelle-like inclusions termed cyanelles which perform photosynthetic C02-fixation in place of chloroplasts. By the use of the HPLC-technique, Cyanophora was shown to form glucose, sucrose, maltose, mannitol, ribose, glycerol and trehalose. Extracts from the whole organism and from the eucaryotic host, but not from the cyanelles, convert 14C-labelled UDP-glucose to polyglucan. Synthesis of sucrose from UDP-glucose and fructose-6-P or fructose could not be demonstrated in any extract from Cyanophora. The transfer of metabolites into cyanelles was monitored by the silicone oil filtering technique. The solute spaces for 14Clabelled sorbitol and 3H20 were the same indicating that sorbitol freely penetrated the plasma membrane of cyanelles in contrast to the situation found in chloroplasts. The measurements ofthe solute spaces for the different compounds showed that maltose and sucrose were not accumulated by isolated cyanelles. Other compounds like fructose, fucose, glutamine or glycine had intermediate sizes of their solute spaces. Cyanelles apparently possess a rapidly transporting glucose carrier and not a malate/oxaloacetate shuttle and also not an ATP/ ADP translocator. The carrier composition at the plasma membrane of cyanelles and at the inner envelope membrane of chloroplasts seems to be totally different.

In vitro import of pre‐ferredoxin‐NADP+‐oxidoreductase from Cyanophora paradoxa into cyanelles and into pea chloroplasts

“…Only the internalized and processed mature FNR was protected, regardless if additional thermolysin treatment took place. Data from metabolite exchange studies [10,14] made it possible to simulate a 'cytosolic' environment for cyanelles during the isolation steps and to establish genuine in vitro conditions. Using BSM, cyanelles could be held stable for several hours.…”

“…Cells were harvested, washed once and then suspended in 10× BSM (isoosmotic buffered sugar mixture, pH 8.0) containing the main sugar metabolites in C. paradoxa and the osmotica protective for cyanelle integrity [10].…”

Identification and Characterization of Glycolate Oxidase and Related Enzymes from the Endocyanotic Alga Cyanophora paradoxa and from Pea Leaves

“…Convincing evidence is now manifold, however, that cyanelles are organelles rather than endosymbiotic prokaryotes. Cyanelles have no respiratory electron transport chain (30), and the size of the genome of cyanelles is 5 to 10% of that of free-living cyanobacteria. This is about the genome size of chloroplasts (7).…”

“…For example, the cyanelle genome codes for both Rubisco subunits (18), whereas the chloroplast genome encodes only for the large subunit. Moreover, cyanelles have other transport mechanisms than chloroplasts and probably export glucose instead of triose phosphates (30). Mitochondria and microbodies (peroxisome-like organelles) attached to the cyanelles were observed by EM in Cyanophora (28).…”

Photosynthetic carbon assimilation in Geosiphon pyriforme (K�tzing) F. v. Wettstein, an endosymbiotic association of fungus and cyanobacterium

“…Presumably they represent photosynthetic end products such as polyglucans. Polyglucans are also major end products in photosynthesis of the endocyanelles in Cyanophora paradoxa (Schlichting et al 1990) and in the symbiontic Nostoc of lichens (Feige 1976). No label was transferred into the insoluble fraction when the tracer was applied in darkness.…”