Changes in microtubule arrays during the differentiation of cortical root cells of Raphanus sativus

Cortical microtubule arrays in meristematic and differentiated cortical cells from root tips of Raphanus sativus were studied using both immunofluorescence and dry cleaving. Length, density and orientation of the cortical microtubules were measured. Between individual, non-dividing cells of the meristematic zone the mean microtubule length varied from 0.9 micron to 1.3 micron and the density varied from 1.7 micron to 3.2 micron microtubule/micron 2 membrane. The direction of the cortical tubules, running parallel to each other in individual cells, appeared to be more or less perpendicular to the root axis, at angles of 85 degrees to 95 degrees. In elongated cortical cells, the mean length had increased to values between 2.6 and 6.7 micron, while the density had decreased to 0.9 to 1.9 micron/micron 2. Microtubules remained parallel to each other within one cell, although their angle with the root axis changed to highly variable values: between 10 degrees to 80 degrees. The results clearly show that important changes occur in the cytoskeleton during the differentiation of cortical cells. It is argued that these changes might be related directly to the morphogenesis of these cells.