ORIGIN,DEVELOPMENT, AND GROWTH OF DIFFERENTIATING TRICHOBLASTS IN ELODEA CANADENSIS

Root hairs of Elodea canadensis develop only from cells which undergo a particular series of developmental steps. These cells, the trichoblasts, are formed as the smaller, proximal product of an asymmetric division, and immediately enter a prolonged phase of synthesis. Histochemical tests show that large amounts of RNA and protein accumulate in the vastly enlarged nucleolus and cytoplasm, while histone increases in the enlarging nucleus. Cytophotometry shows that DNA in the nucleus reaches polyploid levels. Throughout the synthetic phase, almost to the point of root hair initiation at 9.5 mm proximal to the meristem initials, vacuolation is delayed and the trichoblasts elongate less extensively. All results suggest that this synthesis is the type which normally follows cell division, but is greatly enhanced in the trichoblast. In contrast, the initially larger atrichoblasts only accumulate RNA, DNA, and protein in the region from 1 mm to 2 mm proximal to the meristem tip, and they then enter a phase of extensive vacuolation and elongation.