Vitamin B12 and the macromolecular composition of Euglena. I. Kinetic analysis of the cell cycle and chloroplast replication

The kinetics of cell division, chloroplast replication and mean DNA/cell of cultures progressing through B₁₂ deficiency do not follow smooth curves, but contain transient plateaus which are consistent mathematically with the hypothesis that one portion of the Euglena cell cycle, the S phase, is differentially extended under B₁₂ deficiency. A computer simulation of the B₁₂-deficient cultures was capable of duplicating the division kinetics of the actual culture. Chloroplast replication in B₁₂-deficient cells is not directly affected by B₁₂ deficiency, but is a function of the division kinetics of the cells. The chloroplasts continue to replicate initially at a high rate after the cells have entered B₁₂ deficiency, and then follow the kinetics of the cells.