Abstract
Petals color of morning glory, Ipomoea tricolor cv. Heavenly blue, changes from reddish-purple to blue during blooming. The color change is caused by an unusual vacuolar pH increase from 6.6 to 7.7 of the adaxicial and abaxicial colored cells. To clarify the alkalization of epidermal vacuoles we focused on vacuolar membrane proteins. We isolated colored protoplasts from buds and full-opened petals 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 of full-opened petals. These results suggest that the vacuolar pH increase of morning glory petals is due to an active transport of Na+ and/or K+ from cytosol into vacuoles through a sodium driven NXH1, which is supported by V-PPase and V-ATPase. This systematic ion transport brought alkalization of vacuolar pH to resulted sky-blue flower petals.
