Integrated Calcium Signaling in Plants

Calcium ion (Ca 2+ ) is the most important universal signal carrier used by living organisms, including plants, to convey information to many different cellular processes. The cytosolic free Ca 2+ concentration ([Ca 2+ ] cyt ) has been found to increase in response to many physiological stimuli, including stress. The Ca 2+ spikes normally result from two opposing reactions, Ca 2+ influx through channels or Ca 2+ efflux through pumps. The removal of increased Ca 2+ from the cytosol to either the apoplast or intracellular organelles requires energized “active” transport. Ca 2+ -ATPases and Ca 2+ /H + antiporters are the key proteins catalyzing this movement. The increased level of Ca 2+ is recognized by some Ca 2+ sensors or calcium-binding proteins, which can activate many calcium-dependent protein kinases. The regulation of gene expression by cellular Ca 2+ is also crucial for plant defense against various stresses. In this chapter several aspects of calcium signaling, such as Ca 2+ requirement, Ca 2+ transporters/pumps (Ca 2+ -ATPases, Ca 2+ /H + antiporter), Ca 2+ signature, Ca 2+ memory, and various Ca 2+ -binding proteins, are presented.