Analysis of growth components in Allium roots.

Root growth was analyzed in Allium cepa L. grown under steady-state conditions at 10, 15 and 25°C by measuring cell sizes along the meristem and mature zones at these three temperatures and in the elongation zone at 15°C. The absolute rate of growth, v(x), was determined as a function of the mean cell number of cells entering a point x of the root axis and their mean length. Likewise, the relative elemental rate of root growth, g(x), and its components, namely, the relative elemental rate of cell formation, r(x), and the relative elemental rate of cell elongation, e(x), were determined, where g(x)=r(x)+e(x). A fine analysis of quantitative and topographical features of cell division and cell enlargement was carried out along the root axis. Finally, a simple hypothesis is proposed for the control of cell growth and cell division by the interaction with the cell mass of two regulatory, signal factors (proliferative and growth), distributed in opposite gradients along the root axis, between the quiescent centre and the mature zone.