Spatial characteristics of calcium signalling:: the calcium wave as a basic unit in plant cell calcium signalling

Many signals that modify plant cell growth and development initiate changes in cytoplasmic Ca2+. The subsequent movement of Ca2+ in the cytoplasm is thought to take place via waves of free Ca2+. These waves may be initiated at defined regions of the cell and movement requires release from a reticulated endoplasmic reticulum and the vacuole. The mechanism of wave propagation is outlined, and the possible basis of repetitive wave formation, Ca2+ oscillations and capacitative Ca2+ signalling is discussed. Evidence for the presence of Ca2+ waves in plant cells is outlined, and from studies on raphides it is suggested that the capabilities for capacitative Ca2+ signalling are also present. The paper finishes with an outline of the possible interrelation between Ca2+ waves and organelles and describes the intercellular movement of Ca2+ waves and the relevance of such information communication to plant development.