Science Track: Mark Staves, Grand Valley State University, Cell and Molecular Biology, “Illuminating the mechanism of plant gravity sensing with blue light”

With more emphasis on long-term space travel, plants will play an important role in both food production and environmental regulation (oxygen production and carbon dioxide uptake) so it becomes more critical to understand the mechanism by which plants perceive gravity. Since 1900 the most widely-accepted model for plant gravity sensing has been the starch-statolith model which proposes that sedimenting intracellular particles are the gravity sensors. A shortcoming of this model is that there are examples of gravity-responsive plants and plant tissues which do not contain sedimenting statoliths. We proposed an alternative model for plant gravity sensing (the gravitational pressure model) in which the entire protoplast is suggested to be the gravity sensor and that the gravity signal is perceived by sensing differential pressure between the protoplast and the extracellular matrix at the top and the bottom of the cell. To test between these models we grew rice roots in media of different densities and monitored gravity-induced curvature. Consistent with the gravitational pressure model, we find that increasing the density of the external medium reduces gravity-induced curvature and increases negative phototropic curvature.