Perception of gravity in the lentil root.

The gravisensing cells (statocytes), responsible for the perception of gravity, are located in the center of the root cap. The statocytes contain voluminous amyloplasts (statoliths) which are capable of moving in the direction of gravity. The sedimentation of the amyloplasts is due to the starch grains, which are much denser than the surrounding cytoplasm. When the starch of these plastids is removed, the statoliths lose their mobility and the roots are no longer able to respond to gravity. When the roots grow in their normal position, the statoliths are sedimented on large aggregates of endoplasmic reticulum. The role of the association between these two types of organelles is still controversial. For some authors, the amyloplast-endoplasmic reticulum complex would play a role in the induction of the gravitropic response. For other authors, this complex would regulate gravitropic curvature and is more likely to be involved in the termination of the response. The goal of the 39F experiment (Biorack) was to dissociate this complex by growing lentil roots in microgravity and to stimulate them on a centrifuge in order to determine if they were still capable of curvature.