Actomyosin-mediated statolith positioning and sedimentation in gravisensing plant cells studied in microgravity

Graviresponding and tip-growing characean rhizoids and protonemata possess a highly efficient actin-based system to control and correct the position of their statoliths, a prerequisite for gravisensing. Acropetally and basipetally acting actomyosin forces and gravity are the components of the statolith positioning system that also directs sedimenting statoliths to cell-type specific ,oraviperception sites at the plasma membrane where the graviresponse is initiated. These results encourage to propose that similar cytoskeleton-mediated mechanisms for gravity sensing may exist in higher plant statocytes.