Water balance and the regulation of stomatal movements

Stomata form a crucial interface between plants and the atmosphere and are essential to the control of water balance in plants. Prolonged soil dehydration or a drop in atmospheric relative humidity lead to a decrease in biomass production, plant water loss and eventually death. For plants to survive, it is essential that stomata close in response to drought conditions. The phytohormone abscisic acid (ABA) has been shown to play a central role in this process. The first part of this chapter reviews the mechanisms by which drought is translated into signals that lead to stomatal closure, and especially the building up of bioactive ABA concentrations in and around guard cells. The second part introduces the biophysical and metabolic mechanisms used by guard cells to control stomatal aperture. Furthermore, we illustrate how these mechanisms are the target of a signal transduction network integrating drought with other environmental signals. Finally, the third part briefly proposes that stomata represent a putative target to engineer desiccation avoidance in plants.