Preprophase Inhibition of Mitosis in Root Meristems

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Abstract
A study has been carried out on both growth and mitoses in roots of onion bulbs germinated directly on different concentrations of various chemicals in tap water. Typical C-mitotic poisons (Tiogamma and colchicine were tested) do not interfer with neither growth (all root primordia can express all their inherent elongation ability = 11–17 mm.) nor mitosis initiation; both degree and course of polyploidization being quite similar to those occurring in growing onion roots. Preprophase poisons, on the contrary, allow growth and mitosis initiation only at threshold concentrations, typical for each chemical. At the threshold value of preprophase inhibition of mitosis, root elongation is not—or very slightly—influenced and mitosis initiation can, not rarely, occur even in roots recovering from a week treatment with the solution. Mitosis delay induced by chemicals is quite comparable to that following irradiation: prophase prolongation seems to be common to the action of both X-rays and preprophase poisons. It seems likely to assume that the C-mitotic disturbances induced by preprophase poisons in growing meristems may have quite another mechanism than those characterizing typical C-mitotic poisons. In the germination experiments the threshold values of preprophase inhibition of mitosis are always higher than in the corresponding experiments on growing roots. Statements of previous workers on the independence of root elongation from cell division have been confirmed.