Arabidopsis CNGC18 Is a Ca2＋-Permeable Channel

Dear Editor, Extracellular Ca2＋ influx focusing at the tips of pollen tubes is the main source of Ca2＋ for the pollen tube tip cytosolic Ca2＋ gradient, which is essential for both polar growth and orientation of pollen tubes in plants, and plasma membrane Ca2＋ channels were proposed to be present in the tips and function as key proteins by mediating and regulating extracellular Ca2＋ influx （for a review, see Guan et al., 2013）.