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How Plants Feel Gravity : a Granular Flow Problem ?
A plant accidentally put in a horizontal position rapidly bends and deforms to recover a vertical position. The ability of plants to feel gravity thus plays a key role in their development and adaptation to environmental changes (gravitropism). A crucial step in this gravisensing occurs in specific cells, the statocytes, which contain small grains of starch. The grains being denser than the surrounding intracellular fluid, they sediment at the bottom of the cell and are supposed to give the direction of gravity. Despite many studies on the subject, the mechanisms at work in statocytes and the link with the active bending of the plant at the macroscopic scale are still poorly understood. To better understand plant gravitropism, we have carried out experiments at the plant scale to study how shoots responds to change in gravity direction and intensity and at the cell scale to observe the dynamics of the grains. The comparison between the granular dynamics and the response of the plant gives information about the mechanisms involved in the gravitropic response.