Referential Descriptions of Cell Proliferation in Roots Illustrated Using Phleum pratense L.

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Abstract
To study the process of cell proliferation in root apices, it is necessary to adopt a referential viewpoint and to move with cells and their descendants as they are displaced through the meristematic zone during growth. This approach is illustrated for epidermal cells in roots of Phleum paratense L., using "referential regions" whose bounds move through the meristem. Cells are defined as lying in a referential region when their apical cross walls lie between the current postions of the bounds, and cell proliferation occurs as cells divide and new cross walls form. In a Phleum root growing at 19 C, single epidermal cells in regions lying initially between 35 and 44 .mu.m from the apex gave rise to between 10 and 16 descendant cells by the time the region had passed out of the meristematic zone ca. 100 h later. In the process, there were changes in the proportions of proliferative and nonproliferative cells in the region, and immigration and emigration of cells occurred over the bounds of the region. These results are discussed in relation to deterministic and stochastic models for cell proliferation.