Metered rehydration in pollen grains When a desiccated pollen grain lands on fertile territory, it rehydrates on the way to activating its growth and metabolic processes. Studying the small plant Arabidopsis , Hamilton et al. have identified a mechanosensory ion channel that responds to the distention of the plasma membrane as the pollen grain rehydrates. With this channel damaged or absent, the pollen grains germinated overenthusiastically but then showed a tendency to burst. Science , this issue p. 438