Plant and Cell Physiology Advance Access originally published online on February 2, 2005
Plant and Cell Physiology 2005 46(3):407-415; doi:10.1093/pcp/pci057
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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
1 Graduate School of Information Science, Nagoya University, Chikusa, Nagoya, 464-8601 Japan
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
5 Corresponding author: E-mail, yoshidak{at}is.nagoya-u.ac.jp; Fax, +81-52-789-5638.
The 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 bud 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. NHX1 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 the 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; Accepted January 14, 2005
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