The Mitotic Cycle Duration in Vicia Faba Root-Tip Meristems with Different Sized Chromosomes

SUMMARY

The mean nuclear volume and the mean volume per cell of c-metaphase chromosomes was greater in meristematic cells of 4-day-old main root-tips than in 14-day-old lateral root-tips of V. faba. The mitotic cycle time (T), measured by tritium autoradiography, was 15.0 hours in main root-tip cells and 18.1 hours in the lateral root-tip cells. The protein content of nuclei extracted from root tips of three ages was subjected to amino acid analysis. This showed that, while total nuclear protein content increased by over three times with a corresponding but smaller increase in chromosome volume, the relative proportions of the constituent amino acids remained constant. The results are consistent with the hypothesis that the metabolic activity and mitotic rate of Vicia faba meristematic cells is positively correlated wih their mean nuclear volume, mean c-metaphase chromosome volume and nuclear protein content. Possible mechanisms are suggested whereby cell time could be directly determined by variation in total nuclear RNA or protein content.