Abstract
To clarify the molecular mechanism of the gravitropism in higher plants, we have isolated many mutants from Arabidopsis with abnomal shoot gravitropism. The shoot gravitropism 2 (sgr2) recessive mutant exhibits abnormal gravitropic response in hypocotyls and inflorescence stems. We have demonstrated that the endodermal cells containing sedimentable amyloplasts are the site of gravity perception in Arabidopsis shoots. However, amyloplasts did not sediment in sgr2. The SGR2 encodes a protein homologous to bovine phosphatidic acid-preferring phospholipase A1, which localizes mainly to vacuolar membrane. To investigate the molecular function of SGR2 in the gravitropism, we performed a genetic screen for the second mutation suppressing the sgr2-1 phenotype. The kiritsu (krt) mutations suppressed abnormal gravitropic response semidominantly and aberrant amyloplasts movement in the endodermal cells of sgr2-1. This suggests that KRT genes are involved in the function of vacuole and in the movement of amyloplasts.
