SOME EFFECTS OF 2,4,5-TRICHLOROPHENOXYACETIC ACID ON MITOTIC CYCLE OF LATERAL ROOT APICAL MERISTEMS OF VICIA FABA

Roots of Vicia faba were given a one hour pulse label with. 3H-TdR (1 μC/ml), either before or after a three hour treatment with a 10-5 M solution of 2,4,5-trichlorophenoxyacetic acid (TCPA). The durations of the various phases of the mitotic cycle were derived from labeled prophase curves, prepared from autoradiographs of lateral root apical meristems. - TCPA was found to lengthen the duration of the mitotic cycle, primarily because it extended the duration of the period of DNA synthesis (S), though post-synthetic interphase (G2) was also longer. No measurements could be made with respect to the duration of presynthetic interphase (G1), because of rapid changes in the lengths of the G2 and S periods following treatment. - As well as extending the duration of S, TCPA treatment also resulted in at least an initial increase in the rate of DNA synthesis and a decrease in the actual number of cells in S. These results have been discussed with respect to the control of the organization of the root apical meristem. © 1969 Springer-Verlag.