Expanding Without Exploding: Measuring and Modeling the Biomechanics of Pollen Hydration

To carry male gametes to female plants, pollen grains must undergo desiccation. They subsequently rehydrate before extending a tube to fertilize the egg cell. Hydration involves dramatic changes in both the turgor pressure and cell wall properties of the pollen. Little is known about the mechanics of hydration, especially the mechanisms that allow the pollen grain to tolerate the large forces that occur. Here we combine mathematical modeling with experimental data to clarify the role of a membrane-bound tension-sensitive ion channel (MSL8) during hydration. This channel is known to be essential for pollen survival during hydration, but its exact role is not known. New data presented here reveal that MSL8 contributes to rapid stabilization of the pollen grain volume during hydration. In the absence of MSL8, the pollen grain continues to expand indefinitely, often leading to overexpansion and bursting. We develop a mathematical model of rehydration dynamics embodying the interplay between turgor pressure, cell wall mechanics, membrane mechanics, and tension-sensitive channels. This model finds, consistent with the data, that the absence of tension-sensitive channels causes continued expansion of the cell.