statolith

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statolith
1. See statocyst.

2. A membrane-bound group of starch grains (see amyloplast) in plant cells that is believed to act as a sensor to gravity. Starch statoliths are found in cells at the root tips and in the tissues close to the vascular bundles in shoots; under the influence of gravity they sink to the bottom of the cell. Their mechanism of action in triggering the transport of growth substances across the plasma membrane is not understood. One theory is that the statoliths exert pressure on membrane systems inside the cell, e.g. the endoplasmic reticulum, which in turn causes differential growth.

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statolith See STATOCYST.