Calcium: a regulation system emerges in plant cells

Abstract

ABSTRACT Calcium occupies a pre-eminent place in the cellular control systems of animals (Campbell, 1983). Because of the cytotoxic effects of calcium, cells pay very particular attention to keeping cytoplasmic calcium levels very much lower than the normal extra-cellular 10−3M level; usually it is in the range 10−8–10−6M. This is accomplished using a variety of calcium-pumping systems located both in the plasma membrane and organelles and together these operate a very efficient calcium-stat system. But, in addition, cells use the temporary elevation of cytoplasmic calcium to between 10−6 and 10−5 M that may follow plasma membrane perturbation and alteration of calcium channel activity, as signals, eliciting a variety of predetermined responses. The concentration of cytoplasmic calcium is sensed by calcium-binding proteins, most notably calmodulin, and the calcium/calmodulin complex in turn modulates the activity of numerous enzymes and proteins. Calcium is also associated with other signalling systems such as IP3 and cyclic AMP.