Microtubules are at the tips of root hairs and form helical patterns corresponding to inner wall fibrils

Abstract

Root hairs have sometimes provided contradictory evidence for microtubule/microfibril parallelism. This tissue was re-examined using optimized conditions for the fixation, before immunofluorescence, of root hairs. In phosphate buffer, microtubules did not enter the apical tip of radish root hairs and were clearly fragmented. However, in an osmotically adjusted microtubule-stabilizing buffer, microtubules were observed within the apical dome and appeared unfragmented. Microtubules are not, therefore, absent from the region where new cell wall is presumed to be generated during tip growth. A spiralling of microtubules was seen at the apices of onion root hairs. Using shadow-cast preparations of macerated radish root hairs, it was confirmed that steeply helical microtubules matched the texture of the inner wall. In onion, the 45 degrees microtubular helices are accompanied by similarly wound inner wall fibrils. Results do not support the view that microtubules are not involved in the oriented deposition of fibrils in root hairs. Instead, they are interpreted in terms of a flexible helical cytoskeleton, which is capable of changing its pitch but is sensitive to fixation conditions.