Plant and Cell Physiology Advance Access originally published online on February 2, 2005
Plant and Cell Physiology 2005 46(2):259-267; doi:10.1093/pcp/pci028
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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
1 Department of Molecular Biomechanics, The Graduate University for Advanced Studies, Okazaki, 444-8585 Japan
2 National Institute for Basic Biology, Okazaki, 444-8585 Japan
3 Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka, 590-0494 Japan
5 Corresponding author: E-mail, shigiida{at}nibb.ac.jp; Fax, +81-564-55-7685.
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 expressed predominantly in the flower limbs at around 12 h before flower opening. It is expressed very sparsly 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.
The nucleotide sequences of InNHX2 cDNA, InNHX2 genomic DNA and cDNA for the
4 Present address: Faculty of Agriculture, Okayama University, Okayama, 700-8530 Japan
Received November 4, 2004; Accepted November 30, 2004
This article has been cited by other articles:
-subunit gene (-sub) of the mitochondrial F1F0 ATP synthase of I. nil have been submitted to the DDBJ database under accession numbers AB194065
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