Calcium homeostasis and potential roles in combatting environmental stresses in plants

Abstract

The calcium (Ca +2 ) molecules being an important intracellular messenger are involved in various signal transduction mechanisms in plants. Many external stimuli such as drought, cold, heat stress, metalloid stress (copper (Cu), cadmium (Cd), nickel (Ni), and arsenic), flooding, and salinity stress increase the free Ca +2 ions in the cytosol. The H + /Ca +2 antiporters and Ca +2 -ATPases actively transport the cytosolic Ca +2 in intracellular organelles or apoplasts. Increase in Ca +2 concentration is sensed by calcium-binding proteins or Ca +2 -sensors which lead to activation of CDPKs (Calcium-dependent protein kinases). These CDPKs regulate various genes responsive to stress to show phenotypic responses against stress stimuli. Hormonal signaling and their crosstalk with Ca +2 have been studied extensively but a thorough understanding of Ca +2 in stress tolerance is limited. This review describes the various aspects of Ca +2 involvement in sensing stress stimuli, signal transduction, role against various stress factors (including temperature extreme, salinity, flooding, metalloids, and drought), the role of Ca +2 in the regulation of physiological processes, and Ca +2 -ATPase.