MITOTIC SYNCHRONY INDUCED IN MERISTEMS OF VICIA FABA BY 5‐AMINOURACIL: RESPONSE OF SYNCHRONIZED CELLS TO DEOXYNUCLEOSIDES

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Abstract
SUMMARY: Root systems of Vicia faba L. were treated with 3.93x10‐3 solutions of 5‐aminouracil (5‐AU). Cells are blocked, apparently at the S‐G2 transition point, and subsequently a wave of synchronized mitoses are seen. The time and the degree of synchronization differed in different meristems. Cells of primordia are blocked by 5‐AU to the same extent as cells of lateral or primary roots but their cells recover more rapidly than those of fully developed roots. Treatment with a solution of deoxyrinucleosides (10‐6 or 10‐7M) immediately after 5‐AU appears to reverse the block at the S‐G2 transition and results, in a number of cases, in an increase in the degree of mitotic synchrony. The evidence presented shows that 5‐AU and deoxynucleosides reach primordia and fully emerged meristems in effective concentrations; no evidence was found for differential permeability to these compounds. It is suggested that differences in the rate of recovery from the inhibition imposed by 5‐AU reflects some physiological differences between cells of different meristems.