Involved in vacuolar formation or function (e.g. formation of vacuolar membrane 'bulbs'). Required for amyloplast sedimentation in the endodermis during shoot gravitropism, which are thus acting as statoliths. Particularly important for the negative gravitropism leading to leaf movement observed in darkness. Forms oligomers. Detected in small organelles membranes. Expressed in roots, hypocotyls, leaves, stems and floral buds, and, at low levels, in siliques. Expressed in young seedlings and progressively confined in the elongation zone of the root during seedlings growth. Abnormal amyloplast sedimentation and shoot gravitropism. Abnormal gravitropism in both inflorescence stems and hypocotyls accompanied by misshapen seeds and seedlings, including leaf movement in darkness. Reduced formation of vacuolar membrane 'bulbs'. The sgr2-1 mutant has no gravitropic response in inflorescence stems but a reduced gravitropic response in hypocotyls.