Submitted to: Plant Signaling and Behavior
Publication Type: Review Article
Publication Acceptance Date: 1/16/2008
Publication Date: 5/1/2008
Citation: Barkla, B.J., Hirschi, K.D., Pittman, J.K. 2008. Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca(2+) exchangers. Plant Signaling & Behavior. 3(5):354-356.
Technical Abstract: Tonoplast-localised proton-coupled Ca(2+) transporters encoded by cation/H(+) exchanger (CAX) genes play a critical role in sequestering Ca(2+) into the vacuole. These transporters may function in coordination with Ca(2+) release channels, to shape stimulus-induced cytosolic Ca(2+) elevations. Recent analysis of Arabidopsis CAX knockout mutants, particularly "cax1" and "cax3", identified a variety of phenotypes including sensitivity to abiotic stresses, which indicated that these transporters might play a role in mediating the plant's stress response. A common feature of these mutants was the perturbation of H(+)-ATPase activity at both the tonoplast and the plasma membrane, suggesting a tight interplay between the Ca(2+)/H(+) exchangers and H(+) pumps. We speculate that indirect regulation of proton flux by the exchangers may be as important as the direct regulation of Ca(2+) flux. These results suggest cautious interpretation of mutant Ca(2+)/H(+) exchanger phenotypes that may be due to either perturbed Ca(2+) or H(+) transport.