Changes in Ca2+ metabolism in Arabidopsis guard cells in response to blue light

Abstract

Phototropins are blue light receptors that mediate responses such as phototropism, chloroplast movement, stomatal opening, and leaf expansion. One candidate signaling molecule from phototropins is cytosolic Ca2+, since phototropins increase the cytosolic Ca2+ in seedlings and mesophyll cells. The potential involvement of Ca2+ in the blue light–dependent activation of plasma membrane H+-ATPase in guard cells has been reported, but it is not yet known whether cytosolic Ca2+ in guard cells increases in response to blue light. We recently studied changes in the cytosolic Ca2+ in guard cells in response to blue light using aequorin-transformed Arabidopsis. We detected no increase in Ca2+ prior to blue light–dependent activation of plasma membrane H+-ATPase that depended on phototropins. But we detected a photosynthesis-dependent Ca2+ increase. Only when the external K+ concentration was low did blue light induce Ca2+ influx based on phototropin-mediated membrane hyperpolarization. In this addendum, I discuss Ca2+ changes in response to blue light in guard cells and phototropin-mediated Ca2+ signaling.