THE COMPARATIVE CELL CYCLE AND METABOLIC EFFECTS OF CHEMICAL TREATMENTS ON ROOT TIP MERISTEMS. I. IOXYNIL

In this study we investigated the cell cycle response of Vicia faba and Pisum sativum root tip meristems to ioxynil treatments at two concentrations, (10^?-4m and 10^?-6m ). After 24 h of treatment at 10^?-4m concentration, O₂ uptake and ATP concentrations were significantly reduced. The mitotic index was reduced and the cell cycle population position was shifted to indicate that previously inhibited cells reformed their nuclei and became tetraploid. Prolonged treatment at this concentration resulted in cell death. Treatment with ioxynil at 10^?-6m reduced the rate of entry into mitosis. Abnormal mitotic figures in all stages were observed, and the ploidy level of mitotically inhibited cells was doubled. These observations indicated that at 10^?-6m concentration ioxynil acts as a preprophase inhibitor, that is, it does not act directly on the mitotic apparatus but does affect processes on which mitosis depends.