Modulates cytoplasmic Ca(2+) concentration and is crucial for proper stomatal regulation in response to elevated levels of external Ca(2+). May function by regulating concentrations of inositol 1,4,5-trisphosphate (IP3), which in turn triggers release of Ca(2+) from internal stores. May play a role in de-etiolation. Predominantly expressed in the shoot, including guard cells. By Ca(2+) (at protein level). Phosphorylation seems to be light-dependent. Reduced growth. Plants silencing CAS show reduced chlorophyll content and early bolting.