Trichoblasts in Hydrocharis. I. Origin. Differentiation, Dimensions and Growth

Abstract

In the root epidermis of Hydrocharis morsus‐ranae L. distinctive trichoblasts, which later grow out as root hairs, are formed by the unequal division of protodermal (immature epidermal) cells. The trichoblast is the more proximal product of this division. Trichoblasts differ from adjacent epidermal cells in manner of growth, in size, amount of cytoplasm, degree of succinic dehydrogenase and cytochrome oxidase activity, and in the structure of their plastids. Plastids in the trichoblasts gradually become colorless and of less complex structure with increasing distance from the root tip, in contrast to those in adjacent epidermal cells. The trichoblasts do not divide, but they elongate to a considerable extent in the most distal 3000 μ of the root tip and less extensively in the next 3000 μ. By contrast the sister cells and their products divide, but the individual products do not become markedly longer than the mother cell until situated more than 3000 μ from the root tip, when they undergo extensive elongation. The trichoblasts are thus characterized by delayed maturation and inhibition of cytokinesis; it is suggested that delayed maturation is a necessary prerequisite for differentiation of root hairs in this and other species.

Pattern in root meristem development in angiosperms

“…In Phleum it is the distal, but in Hydrocharis it is the proximal (Avers, 1963 ;Cutter & Feldman, 1970 ;Peterson & Farquar, 1996). In most of the Liliidae families sampled here containing species with trichoblasts, the proximal sister cell becomes the trichoblast ; however, it is the distal sister in Juncaceae, Restionaceae and Cyperaceae, as well as in Poaceae where half the species were found to lack trichoblasts (Table 1).…”

Functional Conservation of a Root Hair Cell-Specificcis-Element in Angiosperms with Different Root Hair Distribution Patterns

“…This position-dependent hair cell specification results in rows of hair cells along the longitudinal root axis and has been found in Brassicaceae and other eudicot families (Cormack, 1947;Clowes, 2000;Dolan and Costa, 2001; Figure 1). This striped pattern (Type 3) is one of three types of hair cell distribution patterns (Leavitt, 1904;Cormack, 1937Cormack, , 1947Cutter and Feldmann, 1970;Cutter and Hung, 1972;Dolan, 1996;Clowes, 2000;Dolan and Costa, 2001; Figure 1A). In the Type 1 pattern, root hair cells can differentiate from any epidermal cell.…”

Development and Organization of Cell Types and Tissues

“…The GL2 promoter-β-glucuronidase reporter gene fusion construct directs the expression preferentially in future ordinary epidermal cells (atrichoblasts) located over cortical cells, while the trichoblasts do not show the expression and are located over the junction walls of cortical cells. Cytochemical studies have shown that the developing trichoblast of Phleum pratense and Hydrocharis morsus -ranae has greater activities of enzymes such as acid phosphatase, peroxidase, succinic dehydrogenase and cytochrome oxidase than its sister cell and other epidermal cells (Cutter and Feldman 1970a ;Avers and Grimm 1959 ). The trichoblasts also contain more proteins and RNA and organelle-rich cytoplasm.…”