Mechanisms for calcium sensing receptor-regulated stomatal closure in response to the extracellular calcium signal.

In Arabidopsis, extracellular calcium (Ca²⁺(o)) promotes intracellular calcium (Ca²⁺(i)) transients and stomatal closure, which has been found to be regulated by the calcium sensing receptor (CAS). However, the detailed pathways for transducting the Ca²⁺(o) signal by CAS are still unclear. We found that nitric oxide (NO) and the hydrogen peroxide (H₂O₂) accumulated in the guard cell chloroplast were the two elements that act downstream of the CAS signaling and trigger the stomatal closure by prolonging Ca²⁺(i) transients. Here we provide more commentary on CAS-regulated H₂O₂ generation from chloroplast and Ca²⁺(i) transients in response to Ca²⁺(o), as well as other potential mechanisms that may be involved in the CAS signaling pathway.