Abstract
To investigate the molecular mechanism of gravitropism in higher plants, we have isolated Arabidopsis mutants with altered shoot gravitropism. When the wild-type inflorescence stems were placed horizontally, they curved upward about 90o within 90 min. By contrast, a newly isolated sgr9 mutant exihibited only about 50o curvature even after 8 hours gravi-stimulation, and the curvature never reached 90o. No visible morphological phenotype was oveserved in sgr9, except for lateral shoots growing horizontally. The endodermal cells containing sedimentable amyloplasts are the gravity-perceptive cells in Arabidopsis shoot. In Wild-type plants, each endodermal cell has ten to twenty amyloplasts and most of them sedimented to direction of gravity. Besides endodermal cells containing sedimented amyloplasts, there are considerable number of endodermal cells containing a few floating amyloplasts in sgr9 mutant. Interestingly, these phenotypes are distinct from those of other gravitropic mutants including sgr1-8. Molecular cloning of SGR9 is currently underway.
