Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca2+ exchangers
Volume 3, Issue 5
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Pages 354 - 356http://dx.doi.org/10.4161/psb.3.5.5600
Authors: Bronwyn J. Barkla, Kendal D. Hirschi and Jon K. Pittman View affiliations
Tonoplast-localized proton-coupled Ca2+ transporters encoded by cation/H+ exchanger (CAX) genes play a critical role in sequestering Ca2+ into the vacuole. These transporters may function in coordination with Ca2+ release channels, to shape stimulus-induced cytosolic Ca2+ 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 Ca2+/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 Ca2+ flux. These results suggest cautious interpretation of mutant Ca2+/H+ exchanger phenotypes that may be due to either perturbed Ca2+ or H+ transport.
Received: January 9, 2008; Accepted: January 16, 2008