Helicoidal cell-wall texture in root hairs.

It is shown that root hairs of most aquatic plants have a helicoidal cell-wall texture. Cell walls of root hairs of the aquatic/marshland plant Ranunculus lingua, however, have an axial microfibril alignment. The occurrence of a helicoidal wall texture is not limited to root hairs of aquatic plants: the terrestrial plant Zebrina purpusii has a helicoidal root-hair wall texture, too. With the exception of the grasses, the occurrence of root hairs with helicoidal cell walls pertains to species with predetermined root-hair-forming cells, trichoblasts. The rotation mode of the helicoid is species-specific. The average angle between fibrils of adjacent lamellae varies from 23° to 40°. In Hydrocharis morsus-ranae, cortical microtubules have a net-axial orientation and thus do not parallel nascent microfibrils. The deposition of the helicoidal cell wall is discussed.