Abstract
Plants sense gravity and exhibit tropic response, where amyloplast sedimentation appears to be significant for gravity sensing. Recent live-cell imaging revealed, however, that amyloplasts in endodermal cells show complicated movements toward gravity after 90o-reorientation probably due to interaction with organelle and/or cytoskeleton. Therefore, it remains obscure what kind of amyloplast movement is required for gravity sensing. To address this issue, we analyzed gravitropism and amyloplast dynamics under hypergravity condition where sedimentation by gravity is more dominant than other movements. Segments of Arabidopsis inflorescence stem that were perpendicularly subjected to hypergravity (10g) for 30 sec exhibited obvious gravitropism. Real-time imaging of amyloplasts during hypergravity was performed using a recently developed centrifuge microscope. Almost all amyloplasts moved toward hypergravity and some of them reached the bottom side of the plasma membrane within 30 sec of 10g. These results suggest that amyloplast sedimentation toward the bottom of endodermal cell is important for gravity sensing.
