Abstract
The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure. The connection of these receptors to Ca(2+) signals evoked by ABA has proven more difficult to resolve, although it has been implicated by studies of the pyrbactin-insensitive pyr1/pyl1/pyl2/pyl4 quadruple mutant. One difficulty is that flux through plasma membrane Ca(2+) channels and Ca(2+) release from endomembrane stores coordinately elevate cytosolic free Ca(2+) concentration ([Ca(2+)]i) in guard cells, and both processes are facilitated by ABA. Here, we describe a method for recording Ca(2+) channels at the plasma membrane of intact guard cells of Arabidopsis (Arabidopsis thaliana). We have used this method to resolve the loss of ABA-evoked Ca(2+) channel activity at the plasma membrane in the pyr1/pyl1/pyl2/pyl4 mutant and show the consequent suppression of [Ca(2+)]i increases in vivo. The basal activity of Ca(2+) channels was not affected in the mutant; raising the concentration of Ca(2+) outside was sufficient to promote Ca(2+) entry, to inactivate current carried by inward-rectifying K(+) channels and to activate current carried by the anion channels, both of which are sensitive to [Ca(2+)]i elevations. However, the ABA-dependent increase in reactive oxygen species (ROS) was impaired. Adding the ROS hydrogen peroxide was sufficient to activate the Ca(2+) channels and trigger stomatal closure in the mutant. These results offer direct evidence of PYR/PYL/RCAR receptor coupling to the activation by ABA of plasma membrane Ca(2+) channels through ROS, thus affecting [Ca(2+)]i and its regulation of stomatal closure.
Highlights
The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure
Channels and trigger stomatal closure in the mutant. These results offer direct evidence of PYR/PYL/RCAR receptor coupling to the activation by ABA of plasma membrane Ca2+ channels through reactive oxygen species (ROS), affecting [Ca2+]i and its regulation of stomatal closure
Guard cells close the stomatal pore in response to ABA in part by suppressing current through IK,in and activating current through anion channels (ICl) to depolarize the plasma membrane (Blatt, 2000; Kim et al, 2010)
Summary
The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure. The guard cells open and close the stomatal pore by the uptake and loss, respectively, of osmotic solutes, principally of K+, Cl2, and malate (Blatt, 2000; Kim et al, 2010). These transport processes form the visible end of a complex network of interacting regulatory pathways that coordinate plasma membrane and tonoplast and maintain the homeostasis of the guard cell (Chen et al, 2012b; Hills et al, 2012; Wang et al, 2012). The efflux of K+ and anions results in a net loss of osmotic content, reducing the turgor and volume of the guard cells to close the stomatal pore
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have