Growth and ultrastructure of Arabidopsis root hairs: the rhd3 mutation alters vacuole enlargement and tip growth

The root hairs of plants are tubular projections of root epidermal cells and are suitable for investigating the control of cellular morphogenesis. In wild-type Arabidopsis thaliana (L.) Heynh, growing root hairs were found to exhibit cellular expansion limited to the apical end of the cell, a polarized distribution of organelles in the cytoplasm, and vesicles of several types located near the growing tip. The rhd3 mutant produces short and wavy root hairs with an average volume less than one-third of the wild-type hairs, indicating abnormal cell expansion. The mutant hairs display a striking reduction in vacuole size and a corresponding increase in the relative proportion of cytoplasm throughout hair development. Bead-labeling experiments and ultrastructural analyses indicate that the wavy-hair phenotype of the mutant is caused by asymmetric tip growth, possibly due to abnormally distributed vesicles in cortical areas flanking the hair tips. It is suggested that a major effect of the rhd3 mutation is to inhibit vacuole enlargement which normally accompanies root hair cell expansion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47482/1/425_2005_Article_BF01007706.pd

Genetic analysis of root development

The development of roots represents a useful system to study many aspects of plant morphogenesis. Roots display a relatively simple growth pattern and possess radial symmetry in their cell layers. These features aid studies of pattern formation, meristem activity, and cell differentiation. Recent genetic approaches to the study of root development have focused on Arabidopsis thaliana. This research has led to the identification of several genes that regulate morphogenesis in roots. Genes have also been identified that are involved in the ability of roots to respond to various external stimuli, including gravity and obstacles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30975/1/0000648.pd

The TTG Gene Is Required to Specify Epidermal Cell Fate and Cell Patterning in the Arabidopsis Root

The control of cell fate was investigated in the root epidermis of Arabidopsis thaliana . Two distinct types of differentiated epidermal cells are normally present: root-hair-bearing Cells and hairless cells. In wild-type Arabidopsis roots, epidermal cell fate was found to be correlated with cell position, with root-hair cells located over radial walls between cortical cells, and with hairless cells located directly over cortical cells. This normal positional relationship was absent in ttg (transparent testa glabrous) mutants (lacking trichomes, anthocyanins, and seed coat mucilage); epidermal cells in all positions differentiate into root-hair cells. The opposite condition was generated in roots of transgenic Arabidopsis expressing the maize R (R-Lc) gene product (a putative TTG homologue) under the control of a strong promoter (CaMV35S), which produced hairless epidermal cells in all positions. In both the ttg and R -expressing roots, epidermal cell differentiation was affected at an early stage, prior to the onset of cell elongation or root-hair formation. The ttg mutations were also associated with abnormalities in the morphology and organization of cells within and surrounding the root apical meristem. The results indicate that alterations in TTG activity cause developing epidermal cells to misinterpret their position and differentiate into inappropriate cell types. This suggests that, in wild-type roots, TTG provides, or responds to, positional signals to cause differentiating epidermal cells that lie over cortical cells to adopt a hairless cell fate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31169/1/0000068.pd

The anisotropy1 D604N mutation in the Arabidopsis cellulose synthase1 catalytic domain reduces cell wall crystallinity and the velocity of cellulose synthase complexes

Multiple cellulose synthase (CesA) subunits assemble into plasma membrane complexes responsible for cellulose production. In the Arabidopsis (Arabidopsis thaliana) model system, we identified a novel D604N missense mutation, designated anisotropy1 (any1)