Ca²⁺ signaling in Arabidopsis guard cells

Abstract

In living organisms, Ca²⁺ functions as an important second messenger and various physiological processes are dependent on alteration of cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt). In plants, roles of Ca2+ in root growth, pollen tube elongation, light perception, and regulation of stomatal movements have been well studied. However, the mechanism of Ca²⁺ signaling in plant cells remains unclear compared with animal cells. Here we focused on Ca²⁺ signaling in guard cells where [Ca²⁺]_cyt alters in response to various stimuli including phytohormone abscisic acid and extracellular Ca²⁺ concentration ([Ca²⁺]_o). In order to examine dynamic alteration of [Ca²⁺]_cyt in guard cells, we used Arabidopsis expressing a Ca²⁺ indicator fluorescent protein, yellow cameleon. We also report [Ca²⁺]_cyt oscillations in guard cells of several Arabidopsis mutants defective in stomatal regulation in response to [Ca²⁺]_o.