Origins of the plant chloroplasts and mitochondria based on comparisons of 5S ribosomal RNAs

In this paper, we provide macromolecular comparisons utilizing the 5S ribosomal RNA structure to suggest extant bacteria that are the likely descendants of chloroplast and mitochondria endosymbionts. The genetic stability and near universality of the 5S ribosomal gene allows for a useful means to study ancient evolutionary changes by macromolecular comparisons. The value in current and future ribosomal RNA comparisons is in fine tuning the assignment of ancestors to the organelles and in establishing extant species likely to be descendants of bacteria involved in presumed multiple endosymbiotic events.

Diel rhythms in ribulose-1,5-bisphosphate carboxylase/oxygenase and glutamine synthetase gene expression in a natural population of marine picoplanktonic cyanobacteria (Synechococcus spp.)

Diel periodicity in the expression of key genes involved in carbon and nitrogen assimilation in marine Synechococcus spp. was investigated in a natural population growing in the surface waters of a cyclonic eddy in the northeast Atlantic Ocean. Synechococcus sp. cell concentrations within the upper mixed layer showed a net increase of three- to fourfold during the course of the experiment (13 to 22 July 1991), the population undergoing approximately one synchronous division per day. Consistent with the observed temporal pattern of phycoerythrin (CpeBA) biosynthesis, comparatively little variation was found in cpeBA mRNA abundance during either of the diel cycles investigated. In marked contrast, the relative abundance of transcripts originating from the genes encoding the large subunit of ribulose bisphosphate carboxylase/oxygenase (rbcL) and glutamine synthetase (glnA) showed considerable systematic temporal variation and oscillated during the course of each diel cycle in a reciprocal rhythm. Whereas activation of rbcL transcription was clearly not light dependent, expression of glnA appeared sensitive to endogenous changes in the physiological demands for nitrogen that arise as a natural consequence of temporal periodicity in photosynthetic carbon assimilation. The data presented support the hypothesis that a degree of temporal separation may exist between the most active periods of carbon and nitrogen assimilation in natural populations of marine Synecoccoccus spp.

Aspects of the relation between Cyanophora paradoxa (Korschikoff) and its endosymbiotic cyanelles Cyanocyta korschikoffiana (Hall & Claus) - IV. The effects of rifampicin, chloramphenicol and cycloheximide on the synthesis of ribosomal ribonucleic acids and chlorophyll

The effects of the antibiotics rifampicin, cycloheximide, and chloramphenicol on ribosomal RNA synthesis in Cyanophora paradoxa and its endosymbiotic cyanelles, Cyanocyta korschikoffiana , were examined. Rifampicin inhibited synthesis of the cyanelle 23 S and 16 S r-RNA. Chloramphenicol had a similar, though less marked, effect. By contrast, cycloheximide appeared to inhibit synthesis of only the host’s 25 S and 18 S r-RNA. Neither rifampicin nor chloramphenicol had as marked an inhibitory effect on chlorophyll synthesis as did cycloheximide.

Metabolic activities in Cyanophora paradoxa and its cyanelles : II. Photosynthesis and respiration

Isolated cyanelles of Cyanophora paradoxa perform photosystem I and II dependent Hill reactions. The photosynthetic electron transport of the cyanelles does not show special features uncommon in cyanobacteria or chloroplasts of red algae. A preparation of cyanelles performs photosynthetic O2-evolution with approximately 1/3 of the rate of intact Cyanophora, in only, however, the first three minutes of the experiment. All attempts to stabilize the CO2-fixation activity of isolated cyanelles failed. Isolated cyanelles do not perform KCN-sensitive O2-uptake, indicating that respiratory cytochrome oxidase is lacking in cyanelles. O2-consumption by crude extracts from Cyanophora is inhibited by KCN when N-tetramethyl-p-phenylenediamine/ascorbate or NADH but not NADPH are supplied as the electron donors in contrast to the situation in cyanobacteria. These findings suggest that cyanelles do not respire. It is concluded that cyanelles are not so much related to cyanobacteria as formerly believed, but share many properties with chloroplasts of eukaryotic cells.