ESTIMATION OF THE CELL-CYCLE DURATION IN THE ROOT APICAL MERISTEM - AMODEL OF LINKAGE BETWEEN CELL-CYCLE DURATION, RATE OF CELL PRODUCTION, AND RATE OF ROOT-GROWTH

The Rare of Cell Production (RCP) method to measure the duration of th e cell division cycle in the root apical meristem is proposed. The met hod is based on a model of the steady state growing root and implies t hat 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, i n turn, equal to the number of cells completing elongation. The model is based on the following assumptions: (i) the cycle time for all meri stematic cells is the same; (ii) all meristematic cells proliferate; ( iii) the number of cells in a meristem (or in a cell file within the m eristem), N-m, is constant; and (iv) the flux of cells into and out of the nonproliferating elongation zone is the same. The rationale and b asis for these assumptions are considered in derail. The model of link age 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 N(m)l(e))/V, where l(e) is the f inal length of elongated cells. With the aid of the model, the cell-cy cle duration can be estimated with the simply measured variables N-m, V, and l(e). The analysis of the published data demonstrated that in v arious plant species the values of T in the root apical meristem obtai ned with H-3-thymidine and colchicine methods and those calculated wit h the RCP method were in close agreement and the differences were not more than 10%.