Poster: Membrane Transport

Abs # 1214: Mutant analysis of Ca²⁺/H⁺ transporters suggests regulatory interplay among vacuolar transporters

Presenter:	Hirschi, Kendal , kendalh@bcm.tmc.edu
Authors	Hirschi, Kendal  (A)   Ning-Hui, Cheng  (A)   Pittman, Jon K (A)   Shigaki, Toshiro  (A)
Affiliations:	(A): Baylor College Medicine

The Arabidopsis Ca²⁺/H⁺ transporters, CAX1 (cation exchanger 1), CAX2 and CAX3 may be important components in determining the cytosolic concentrations of Ca²⁺ and other metals. Here we present data regarding the isolation and characterization of insertion mutants of these transporters. Under normal growth conditions, these mutants show subtle morphological phenotypes; however, there are alterations in other vacuolar transporters. For example, all three mutants display at least a 25% reduction in vacuolar H⁺-ATPase activity. The cax2 mutant displays a 61% reduction in vacuolar Mn²⁺/H+ antiport activity but no change in vacuolar Ca²⁺/H⁺ antiport activity, while the cax1 mutant demonstrates a 50% reduction in vacuolar Ca²⁺/H⁺ antiport activity, a 36% increase in tonoplast Ca²⁺-ATPase activity, and increased expression of the putative vacuolar Ca²⁺/H⁺ antiporters CAX3 and CAX4. We are in the process of characterizing CAX double mutants and are currently investigating the nature of the compensatory changes among these transporters.