Effect of 2,4-D on cell proliferation and elongation in the roots of Arabidopsis thaliana

We investigated the effect of 2,4-D (2,4-dichlorophenoxyacetic acid) at concentrations of 1.5, 15, 30, and 60 nM on the growth of the main root of 3-7-d-old plants of Arabidopsis thaliana L. On the basis of measurements of the rate of root growth, lenght of fully elongated cells, and the number of cells in the meristem and elongation zone, we calculated the rates of cell proliferation and their transition to elongation, duration of cell cycle, and life span of cells in the meristem. At a concentration of 1.5 nM, 2,4-D did not affect these characteristics. At concentrations above 1.5 nM, 2,4-D noticeably retarded root growth, which was accounted for by a reduction in the length of cells that completed elongation, deceleration of cell proliferation and their transition to elongation, and prolongation of cell cycle and life span of the cells in the meristem. Thus, auxin decelerated root growth not only as a result of suppression of cell elongation but also at the higher concentrations via retardation of cell divisions in the meristem and their transition to elongation.