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Plant Cell Advance Online Publication
Published on January 2, 2003; 10.1105/tpc.007385

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Received August 30, 2002
Accepted November 14, 2002

The Arabidopsis cax1 Mutant Exhibits Impaired Ion Homeostasis, Development, and Hormonal Responses and Reveals Interplay among Vacuolar Transporters

Ning-Hui Cheng 1, Jon K. Pittman 1, Bronwyn J. Barkla 2, Toshiro Shigaki 1, and Kendal D. Hirschi 3*

1 United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030
2 Instituto de Biotecnología, Universidad Nacional Autónoma de México, Colonia Miraval, Cuernavaca, Morelos 62250, Mexico
3 United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030; Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas 77030; Vegetable and Fruit Improvement Center, Texas A&M University, College Station, Texas 77845

* To whom correspondence should be addressed. E-mail: kendalh{at}bcm.tmc.edu.

The Arabidopsis Ca2+/H+ transporter CAX1 (Cation Exchanger1) may be an important regulator of intracellular Ca2+ levels. Here, we describe the preliminary localization of CAX1 to the tonoplast and the molecular and biochemical characterization of cax1 mutants. We show that these mutants exhibit a 50% reduction in tonoplast Ca2+/H+ antiport activity, a 40% reduction in tonoplast V-type H+-translocating ATPase activity, a 36% increase in tonoplast Ca2+-ATPase activity, and increased expression of the putative vacuolar Ca2+/H+ antiporters CAX3 and CAX4 . Enhanced growth was displayed by the cax1 lines under Mn2+ and Mg2+ stress conditions. The mutants exhibited altered plant development, perturbed hormone sensitivities, and altered expression of an auxin-regulated promoter-reporter gene fusion. We propose that CAX1 regulates myriad plant processes and discuss the observed phenotypes with regard to the compensatory alterations in other transporters.






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