Abstract
Plants utilize gravitational stimulus as a directional cue of their growth. We have studied the molecular genetic mechanism of gravitropism of Arabidopsis inflorescence stems. Gravitational stimulus is perceived as amyloplasts movement toward the direction of gravity in the endodermal cell. Amyloplasts in the endodermal cells did not sediment to the direction of gravity sgr (shoot gravitropism) 2, sgr3, and zig/sgr4 mutants which exhibit little or reduced gravitropism. Molecular cloning of these SGR genes have demonstrated that vacuoles have higher-ordered novel function for gravity perception, and that membrane traffic between the trans-Golgi network and vacuoles is important for such vacuolar function. Live cell imaging system enabled us to show that functions and membrane dynamics of vacuoles are closely related to the amyloplasts movement. To elucidate genetic network involved in vacuolar function and its membrane dynamics, we have performed molecular genetic studies of phospholipase A1-like SGR2 and Qb-SNARE ZIG/SGR4/VTI11.
