Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca~(2+) exchangers

摘要

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 shapestimulus-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.