Poster: Tropisms

Abs # 653: Dynamics of amyloplasts and vacuolar membrane during gravi-perception in Arabidopsis inflorescence stem

Presenter:	Saito, Chieko , chie@bs.aist-nara.ac.jp
Authors	Saito, Chieko  (A)   Terao-Morita, Miyo  (A)   Tasaka, Masao  (A)
Affiliations:	(A): Nara Institute of Science and Technology

The shoot of higher plants shows negative gravitropism in general. We have isolated many abnormal shoot gravitropism mutants (sgr) in Arabidopsis to elucidate its molecular mechanisms. Our previous works have shown that endodermal layer of inflorescence stem sense the gravity orientation. Sedimentable amyloplasts in the endodermal cell are regarded as statoliths. We revealed that those amyloplasts are wrapped by vacuolar membrane, and suspended within inside of the vacuole by electron microscopy. Our analyses of sgr2 sgr3, and sgr4 mutants strongly suggest that the vacuole and amyloplasts interact intimately, and they may play important function in the perception of gravity orientation. To reveal the early key steps for gravity perception, we constructed vertical stage microscope system to visualize the behavior of both organelles in living endodermal cells directly. We found that, before applying gravi-stimuli, amyloplasts are sedimenting but most of them are leaping in wild-type, while those in sgr2 sgr3, and sgr4 are considerably static. After applying gravi-stimuli, most of amyloplasts are translocate within transvacuolar strands in wild-type, while only slight movements are detected in those mutants. These movements are confirmed by the visualization of vacuolar membrane.