Integrated Calcium Signaling in Plants

Abstract

Calcium ion (Ca2+) is the most important universal signal carrier used by living organisms, including plants, to convey information to many different cellular processes. The cytosolic free Ca2+ concentration ([Ca2+]) has been bound to increase in response to many physiological stimuli, including stress. The Ca2+ spikes normally result from two opposing reactions, Ca2+ influx through channels or Ca2+ efflux through pumps. The removal of increased Ca2+ from the cytosol to either the apoplast or intracellular organelles requires energized "active" transport. Ca2+-ATPases and Ca2+/H+ antiporters are the key proteins catalyzing this movement. The increased level of Ca2+ is recognized by some Ca2+ sensors or calcium-binding proteins, which can activate many calcium-dependent protein kinases. The regulation of gene expression by cellular Ca2+ is also crucial for plant defense against various stresses. In this chapter several aspects of calcium signaling, such as Ca2+ requirement, Ca2+ transporters/pumps (Ca2+-ATPases, Ca2+/H+ antiporter), Ca2+ signature, Ca2+ memory, and various Ca2+-binding proteins, are presented.