Dr Olivier Pouliquen
An active granular liquid at the origin of the sensitivity of plants to gravity
Abstract: A plant accidentally put in a horizontal position bends and deforms to recover a vertical position. 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 form miniature granular piles at the bottom of the gravisensing cells. How such a sensor works and can detect inclination
is unclear, as granular materials like sand are known to display flow threshold and finite avalanche angle due to friction and interparticle jamming. Here, we address this issue by combining direct visualization of statoliths avalanches in plant cells and experiments in biomimetic cells made of microcavites filled with a suspension of heavy Brownian particles. We show that, despite their granular nature, statoliths move and respond to the weakest angle, as a liquid clinometer would do. Comparison between the biological and biomimetic systems reveals that this liquid-like behavior comes from the cytoskeleton activity, which agitates statoliths with an apparent temperature one order of magnitude larger than actual temperature. Our results shed light on the key unlocking role of these active fluctuations for explaining the remarkable sensitivity of plants to inclination.
Co-authors: A. Berut, H. Chauvet, V. Legue, B. Moulia, Y. Forterre
is unclear, as granular materials like sand are known to display flow threshold and finite avalanche angle due to friction and interparticle jamming. Here, we address this issue by combining direct visualization of statoliths avalanches in plant cells and experiments in biomimetic cells made of microcavites filled with a suspension of heavy Brownian particles. We show that, despite their granular nature, statoliths move and respond to the weakest angle, as a liquid clinometer would do. Comparison between the biological and biomimetic systems reveals that this liquid-like behavior comes from the cytoskeleton activity, which agitates statoliths with an apparent temperature one order of magnitude larger than actual temperature. Our results shed light on the key unlocking role of these active fluctuations for explaining the remarkable sensitivity of plants to inclination.
Co-authors: A. Berut, H. Chauvet, V. Legue, B. Moulia, Y. Forterre
Biography: Olivier Pouliquen is CNRS Research Director at IUSTI, Aix-Marseille University. His research concerns the physics of granular materials and dense suspensions. Since a few years, he has started to study plant gravitropism both at the macroscopic and cellular level. In 2017, he has been awarded the prestigious Mergier-Bourdeix prize.
The organisers are grateful to the UK Fluids Network who generously allowed us to use pictures from their website and the various photos competitions they organise