Building a hair: tip growth inArabidopsis thalianaroot hairs

Abstract

The Arabidopsis thaliana root hair is used as a model for studying tip growth in plants. We review recent advances, made using physiological and genetic approaches, which give rise to different, yet compatible, current views of the establishment and maintenance of tip growth in epidermal cells. For example, an active calcium influx channel localized at the tip of Arabidopsis root hairs has been identified by patch-clamp measurements. Actin has been visualized in vivo in Arabidopsis root hairs by using a green-fluorescent-protein-talin reporter and shown to form a dense mesh in the apex of the growing tip. The kojak gene, which encodes a protein similar to the catalytic subunit of cellulose synthase, is needed in the first stages of hair growth. A role for LRX1, a leucine-rich repeat extensin, in determining the morphology of the cell wall of root hairs has been established using reverse genetics. The new information can be integrated into a general and more advanced view of how these specialized plant cells grow.

Cell wall extensibility during branch formation in the xanthophycean alga Vaucheria terrestris

“…Similar subapical extension was also observed in the cell wall isolated from the growing Root hair formation is another extensively investigated example (Carol and Dolan 2002).…”

Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

“…Root hairs and pollen tubes are the best-studied plant cells that elongate through the process of tip growth (28,75,156). Infection threads develop from growing root hairs, are thought to be tip-growing structures, and therefore most likely elongate by using at least some of the machinery that was supporting root hair growth before infection took place.…”

“…There is a large body of work devoted to understanding the roles played by actin filaments and microtubules in cytoplasmic streaming of plant cells (28,75,87,135,149,178). In the case of tip-growing cells, the accumulated evidence suggests that vesicle and organelle movement in cytoplasmic streams involves myosin-based motors moving along actin filaments.…”

“…Studies with ion-specific dyes have shown that growing root hairs and pollen tubes exhibit tip-focused gradients of Ca 2ϩ (28,75). In growing root hairs the concentration of this ion at the tip, just below the plasma membrane, is about 1 M and decays to a basal concentration of about 100 nM within 20 m (13, 188).…”

“…Suggested roles for Ca 2ϩ include influencing cell wall strength and extensibility, controlling actin dynamics, and controlling vesicle fusion at the grow- (28,75,138). Of course, these roles need not be mutually exclusive.…”