Estimation of the cell-cycle duration in the root apical meristem: a model of linkage between cell-cycle duration, rate of cell production, and rate of root growth

The Rate of Cell Production (RCP) method to measure the duration of the cell division cycle in the root apical meristem is proposed. The method is based on a model of the steady state growing root and implies that the number of cells produced in the meristem per unit time has to be equal to the number of cells shifting to the elongation zone and, in turn, equal to the number of cells completing elongation. The model is based on the following assumptions: (i) the cycle time for all meristematic cells is the same; (ii) all meristematic cells proliferate; (iii) the number of cells in a meristem (or in a cell file within the meristem), Nm, is constant; and (iv) the flux of cells into and out of the nonproliferating elongation zone is the same. The rationale and basis for these assumptions are considered in detail. The model of linkage for the average duration of the cell division cycle (T), the rate of cell production in the meristem, and the overall root growth rate (V) is described as following T = (ln2 Nmle)/V, where leis the final length of elongated cells. With the aid of the model, the cell-cycle duration can be estimated with the simply measured variables Nm, V, and le. The analysis of the published data demonstrated that in various plant species the values of T in the root apical meristem obtained with3H-thymidine and colchicine methods and those calculated with the RCP method were in close agreement and the differences were not more than 10%.