Abstract
Arabidopsis shoot gravitropism (sgr) 6 mutant exhibits a slower gravitropic response than wild-type. We found that SGR6 is expressed in the epidermis, endodermis, vascular tissue and interfascicular cells in the stem. The endodermis is an essential cell layer for the gravity-sensing in the stem. In the endodermal cells, amyloplasts are enclosed by a vacuolar membrane. Amyloplast movement toward the direction of gravity is important for the gravity-sensing, and it requires the dynamic structures of the vacuolar membrane. Live cell imaging analysis showed that, in wild-type, the dynamics of the vacuolar membrane and amyloplast were maintained during the 30-minute observation. On the other hand, in sgr6 mutant, the dynamics of the vacuolar membrane and amyloplast were completely lost after 30 minutes of observation. This result indicates that SGR6 plays a role to maintain the dynamics of the vacuolar membrane and amyloplast in the endodermal cells. To know the correlation between the phenotype observed in the endodermal cells and that of gravitropism, the analysis of transgenic plants expressing SGR6 under the endodermis-specific promoter in sgr6 mutant is now ongoing.
