Plant and Cell Physiology Advance Access first published online on February 2, 2005
This version published online on February 3, 2005
Plant and Cell Physiology, doi:10.1093/pcp/pci028
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1 Department of Molecular Biomechanics, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
* To whom correspondence should be addressed. The reddish-purple buds of the wild-type Japanese morning glory (Ipomoea nil) change into blue open-flowers, and the shift in the flower coloration correlates with an increase in the vacuolar pH of the flower epidermal cell. In the mutant deficient in the InNHX1 gene for the vacuolar Na+/H+ antiporter, the vacuolar alkalization occurs only partially, and reddish-purple buds become purple open-flowers. While most of the plant NHX genes characterized are generally expressed in leaves, stems and roots and induced by NaCl treatment, the InNHX1 gene is predominantly expressed in the flower limbs at around 12 h before flower-opening. It is expressed very scarcely in leaves, stems and roots, and no induction occurs in response to NaCl treatment. Here, we identified a novel vacuolar Na+/H+ antiporter gene InNHX2, which is expressed in leaves, stems and roots and is induced in response to NaCl treatment. In addition, relatively higher expression of InNHX2 was observed in the flower limbs shortly before flower-opening. We also discovered that both the InNHX1 and InNHX2 proteins can catalyze both Na+ and K+ transport into vacuoles. These results suggest that InNHX2 performs dual functions: to confer salt tolerance on the plant and to promote partial vacuolar alkalization in the petals. The implication is that the InNHX2 protein is probably one of the components responsible for converting reddish-purple buds into purple open-flowers by partially increasing the vacuolar pH in the absence of major InNHX1 activity.
Received November 4, 2004
Accepted November 30, 2004
Rapid Paper
Characterization of a Novel Na+/H+ Antiporter Gene InNHX2 and Comparison of InNHX2 with InNHX1, Which Is Responsible for Blue Flower Coloration by Increasing the Vacuolar pH in the Japanese Morning Glory
2 National Institute for Basic Biology, Okazaki 444-8585, Japan
3 Department of Molecular Biomechanics, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan; National Institute for Basic Biology, Okazaki 444-8585, Japan
4 Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-0494, Japan
Shigeru Iida, E-mail: shigiida{at}nibb.ac.jp
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