Phylogenetic origin of the chloroplast

On plastid symbiosis in Tontonia appendiculariformis (Ciliophora, Oligotrichina)

Many hundreds of isolated plastids, in a good state of preservation in their living host, the planktonic ciliate Tontonia appendiculariformis (Oligotrichina), have been studied by electron microscopy. These distinctive plastids, located at the periphery of the host's body, which do not belong to complete symbiotic algae, are described in detail. All are bounded by three membranes. Although degenerating plastids were observed none were ever seen in division. Their possible origin, the significance of the three plastid membranes, and the degree of symbiosis established are discussed. From their organization, these plastids may have originated from several species of chromophyte algae, such as dinophyceae, Prymnesiophyceae, and Bacillariophyceae or Chrysophyceae. Because of their absence of division and of their possible degeneration, they are probably not integrated genetically. However, they appear to survive for some time and to remain functional. There is evidence that the outermost third plastid membrane arises from the host ciliate. Finally, hypotheses are proposed to explain the incorporation of the plastids into the ciliate, and their possible role in building cortical polysaccharide plates.

Nucleo-cytoplasmic interactions in the regulation of thymidine phosphorylation in Acetabularia

The activity of dT kinase (EC. 2. 7. 1. 75) was estimated during the development of nucleate and anucleate cells inAcetabularia. Enzyme activity increases as the cap attains its maximum diameter (Bannwarth & Schweiger 1975). Regulation of the dT kinase activity is observed even in the absence of the cell nucleus. Twelve to fifteen days after enucleation dT kinase activity increase sharply as the cap reaches its maximum diameter and decreases 5 days later. The increase is inhibited by puromycin, chloramphenicol, rifampicin and ethidium bromide but not by cycloheximide. These findings indicate that protein synthesis on 70S organelle ribosomes is involved in the regulation of the dT kinase. Since activities of mixtures from low activity cell extracts and from high activity cell extracts are additive, it is concluded that the regulation is not mediated through an activator protein but rather throughde novosynthesis of the enzyme protein.