ИСТИНА

The transition of meristematic cells to elongation is needed for maintenance of the root growth rate since the duration of the root cell elongation is very short. The rate of cell transition to elongation (differentiation) is regulated by two groups of independent processes. The first ones regulate the life-span of cells in meristem – the duration of the period when cells located at various distances from the root tip reach the basal boundary of meristem and begin to elongate. The seconds one regulate the rate of the cell proliferation during the life-span of cells in meristem. Transzeatin slows down the root growth rate and the rate of the transition of meristematic cells to elongation as a result of prolongation of mitotic cycles. The life-span of cells in meristem does not change. The number of meristematic cells in one file decreases but it is the result of the inhibition of cell proliferation but not the acceleration of the cell transition to elongation (differentiation). The roots of triple mutants ipt3ipt5ipt7 in which cytokinin synthesis is slowed down grow at higher rate than control roots. The number of meristematic cells in one file in these roots is greater than in roots of wild type. It is the result of the higher rate of cell transition to elongation and the acceleration of cell proliferation. The life-span of cells in meristem is shorter than in control roots. Analogical results were obtained for roots of some cytokinin signaling mutants. Thus, slowing root growth, when treated with cytokinins, or acceleration growth with reduction of the concentration of endogenous cytokinin or weakening of their signaling are associated with changes in the duration of mitotic cycle. Alyhough, there is a view that cytokinines regulate the cell transition to differentiation, and thereby changing the rate of root growth and meristem size, our date rather showed that cytokinis affects the cell cycle duration. This work was partially supported by Grant of RFFI 15-04-02502.