Coupling diurnal cytosolic Ca2+ oscillations to the CAS-IP3 pathway in Arabidopsis

Various signaling pathways rely on changes in cytosolic calcium ion concentration ([Ca 2+ ] i ). In plants, resting [Ca 2+ ] i oscillates diurnally. We show that in Arabidopsis thaliana , [Ca 2+ ] i oscillations are synchronized to extracellular Ca 2+ concentration ([Ca 2+ ] o ) oscillations largely through the Ca 2+ -sensing receptor CAS. CAS regulates concentrations of inositol 1,4,5-trisphosphate (IP 3 ), whichinturndirects release of Ca 2+ from internal stores. The oscillating amplitudes of [Ca 2+ ] o and [Ca 2+ ] i are controlled by soil Ca 2+ concentrations and transpiration rates. The phase and period of oscillations are likely determined by stomatal conductance. Thus, the internal concentration of Ca 2+ in plant cells is constantly being actively revised.