Insights into the microstructures of hygroscopic movement in plant seed dispersal.

As non-motile organisms, plants develop means to spread their progenies. Hygroscopic movement is a very common mechanism employed in seed dispersal. This type of movement is created when the tissue desiccates and the cell walls dry and shrink. A contraction force develops, the direction and strength of which depends on the architecture of the tissue. This force may be utilized for a simple release of seeds, their catapultion, and for pushing seeds along the soil to a germination locus. We review the formation of a bend, a twist and a coil within various dispersal apparatuses as a reaction to the dehydration of the tissue. We compare the microscopic structures of hygroscopic devices supporting slow or fast movement, adaptations to dry or wet climates, and single use versus repeated movement. We discuss the development of the disconnecting tissues in relation to the development of a hygroscopic mechanism. As plant cultivation is dependent on seed dispersal control, we demonstrate that during the domestication of sesame and wheat, seed dispersal is avoided not due to a defective hygroscopic tissue, but rather a missing dehiscence tissue. Seed dispersal is a crucial stage in the life cycle of plants. Thus, hygroscopic movement plays a central part in plant ecology and agriculture.