Stomata under salt stress—What can mechanistic modeling tell us?

Stomata are pores that form between pairs of guard cells and are commonly found in the leaf epidermis. The pores allow gaseous exchange between the inner air spaces of the leaf and the atmosphere, opening for CO2 entry to support photosynthesis and closing to reduce transpirational water loss. Guard cell membrane transport and its coordination play a central part in regulating the pore aperture. We know how guard cells respond to light, CO2 and drought with sufficient detail to model with quantitative accuracy their mechanics. By contrast, there is surprisingly little detail about the impact of salt stress on guard cells. Here we review the topic and introduce Na+ transport within the proven OnGuard3 modeling platform to question the mechanics of stomatal responses to salinity. The analysis indicates a critical role for ABA-mediated Ca2+ signaling as an early and overriding process leading to stomatal closure, a beneficial behavior for plants in the face of salt stress.