Plant and Cell Physiology Advance Access published online on February 2, 2005
Plant and Cell Physiology, doi:10.1093/pcp/pci057
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1 Graduate School of Information Science, Nagoya University, Chikusa, Nagoya 464-8601 Japan
* To whom correspondence should be addressed. Petal color of morning glory, Ipomoea tricolor cv. Heavenly blue, changes from purplish red to blue during flower-opening. This color change is caused by an unusual increase in vacuolar pH from 6.6 to 7.7 in the colored adaxial and abaxial cells. To clarify the mechanism underlying the alkalization of epidermal vacuoles in the open petals we focused on vacuolar H+-ATPase (V-ATPase), H+-pyrophosphatase (V-PPase) and an isoform of Na+/H+ exchanger (NHX1). We isolated red and blue protoplasts from the petals in buds and fully open flower, respectively, and purified vacuolar membranes. The membranes contained V-ATPase, V-PPase and NHX1, which were immunochemically detected, with relatively high transport activity. Na+/H+ exchanger could be detected only in the vacuolar membranes prepared from flower petals and its protein level was the highest in the colored petal epidermis of the open flower. These results suggest that the increase of vacuolar pH in the petals during flower-opening is due to active transport of Na+ and/or K+ from cytosol into vacuoles through a sodium- or potassium-driven Na+(K+)/H+ exchanger NXH1 and that V-PPase and V-ATPase may prevent the over-alkalization. This systematic ion transport maintains the weakly alkaline vacuolar pH, producing the sky-blue petals.
Received January 6, 2005
Revised January 14, 2005
Accepted January 20, 2005
Rapid Paper
The Involvement of Tonoplast Proton Pumps and Na+(K+)/H+ Exchangers in the Change of Petal Color During Flower-Opening of Morning Glory, Ipomoea tricolor cv. Heavenly Blue
2 Graduate School of Human Informatics, Nagoya University; Chikusa, Nagoya 464-8601 Japan
3 Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601 Japan
4 Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-8585 Japan
Kumi Yoshida, E-mail: yoshidak{at}is.nagoya-u.ac.jp
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