Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2002
Publication Date: 2/3/2003
Citation: CHENG,N., PITTMAN,J.K., BARKLA,B.J., SHIGAKI,T., HIRSCHI,K. ., THE ARABIDOPSIS CAX1 MUTANT EXHIBITS IMPAIRED ION HOMEOSTASIS, DEVELOPMENT, AND HORMONAL RESPONSES, AND REVEALS INTERPLAY AMONG VACUOLAR TRANSPORTERS, THE PLANT CELL, 2003. v. 15. p. 347-364. Interpretive Summary: Calcium levels are important in determining how a plant responds to the environment. Both plants and animals regulate calcium levels by modifying the movement of this substance using various transporters. If calcium levels remain low inside the plant cells- the plant remains at rest. We speculate that the calcium transporters are not functioning during these rest periods. When calcium levels rise- plants alter their growth and development. These alterations are presumed to require the activity of calcium transporters. In this work, we document how plants alter their growth and development when calcium transporters are never allowed to function. These findings help us determine the importance of calcium transporters in plant growth and development. Potentially, insights from these finding can help us increase plant yield.
Technical Abstract: The Arabidopsis Ca2+/H+ transporter, CAX1 (cation exchanger 1), may be an important regulator of intracellular Ca2+ levels. We describe here the 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 V-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 a myriad of plant processes, and discuss the observed phenotypes in lieu of the compensatory alterations in other transporters.