Two kinds of roots, differing in width, can be grown from the regularly watered rhizome of Carex setifolia in strict cultural conditions. When plants are subjected to drought, which increases water deficit in the plants, root growth stops and the root tip necroses while lateral root initiation is stimulated. After watering again, growth of aerial parts is resumed, either from the oldest tiller after moderate desiccation, or from new tillers. The roots with the greatest diameter show an increase in thickness just behind the tip. The thickening lasts only 48 h after the beginning of watering, then roots grow normally again. Sometimes, several roots initiate from the thickened portion of the tuberized zone.An histological study of the normal roots and tuberized zones indicates that the difference occurs in the cortex. Whereas the cortex is lacunar in normal roots, it looks dense in tuberized parts of the roots and consists of radial rows of cells apparently generated from an extra-endodermic layer. This generative zone is normally present, though undeveloped and nonfunctional in normal roots of C. setifolia. Furthermore, a large amount of starch is found in the cortex of the thickened parts of the roots.
Interacting Glutamate Receptor-Like Proteins in Phloem Regulate Lateral Root Initiation in Arabidopsis