GRAVITY SENSING IN TIP-GROWING CELLS

In addition to the statocytes of roots and shoots, a number of tip-gro wing cells also sense gravity, which influences the cells' growth and development. Since these tip-growing cells are highly suitable for obs ervations in vivo, the movement and sedimentation of their statoliths can be studied in detail, Experimental manipulation by centrifugation, drug application, optical tweezers or microgravity can be monitored b y light microscopy. The statoliths are localized in distinct cytoplasm ic areas by interactions with actin filaments or microtubules, and the ir sedimentation seems to be narrowly confined, Since gravisensing and the graviresponse take place within the same cell, the gravitropic si gnal transduction chain is not complicated by signal transmission betw een sensing and responding cells. Studies on tip-growing cells have no w enabled the formulation of models explaining positive and negative g ravitropism.