Helical microtubular arrays in onion root hairs.

The higher order patterns to which individual plant microtubules contribute are not yet fully described, perhaps because of the problems of reconstructing whole-cell conformations from electron microscope (EM) thin sections. Because microtubules may govern the way in which cellulose microfibrils are deposited in the plant cell wall, it is important to determine the range of permissible conformations for this has implications for the understanding of wall texture. Often, but not always, the EM shows that microtubules occur roughly transversely to the plant cell's long axis and they are usually conceived of as contributing to a series of 'hoops'. However, based on evidence that microtubules can be long relative to the cell's circumference and on the interconnected nature of the cytoskeleton, it was recently proposed that microtubules might be wound helically around the cell; the helical pitch being influenced by the expansion characteristics of the cell. By using whole-cell immunofluorescence and monoclonal antibodies to tubulin, evidence is now presented which confirms that unambiguous helices occur in formaldehyde-fixed onion root hairs.