Spatial characteristics to 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 Ca 2+ . The subsequent movement of Ca 2+ in the cytoplasm is thought to take place via waves of free Ca 2+ . 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 reticulum wave formation, Ca 2+ oscillations and capacitative Ca 2+ signalling is discussed. Evidence for the presence of Ca 2+ waves in plant cells is outlined, and from studies on raphides it is suggested that the capabilities for capacitative Ca 2+ signalling are also present. The paper finishes with an outline of the possible interrelation between Ca 2+ waves and organelles and describes the intercellular movement of Ca 2+ waves and the relevance of such information communication to plant development.