Quantitative Assessment of Ultrastructural Changes in Primary Roots of Corn (Zea mays L.) after Geotropic Stimulation: II. Curving and Noncurving Zones of the Root Proper

In outer cortical cells of corn (Zea mays L.) roots we made ultrastructural comparisons between the geotropically responding (661 nm irradiated) and nonresponding (dark control) roots in both the curving and noncurving regions of the root. In the control treatment, Golgi apparatus (dictyosomes) and mitochondria exhibited centrifugal distribution (taking the stele as the center) in both regions of the roots (the organelles localized in the top of the cells in the upper tissues, and in the bottom of the cells in the lower tissues). In the geotropically responding roots, the distribution patterns were the same as those of the controls. However, in the zone of curvature the dictyosomes (but not the mitochondria) were randomly distributed in the cells of the upper tissues. This change in pattern of dictyosome distribution could be related to the change in cell elongation of upper cells.