Abstract
Petal color of morning glory, Ipomoea tricolor cv. Heavenly blue, changes from reddish-purple to blue during blooming. The flower color change was caused by vacuolar pH increase from 6.6 to 7.7.1) To clarify the mechanism we studied on proton pumps and Na+/H+ exchanger in epidermal vacuolar membrane.
Vacuolar membrane were prepared form the colored protoplasts of buds and fully opened flower petals. Immunoblot analysis of vacuolar membrane revealed that V-PPase increased in opened flowers compared with that in buds. Na+/H+ exchanger was not detected in buds but it was markedly accumulated in the opened flowers. This Na+/H+ exchanger was confirmed to be localized on only vacuolar membrane of petals. Vacuolar pH increase might due to transport cytosolic Na+ and/or K+ into vacuole by Na+/H+ exchanger driven by a pH gradient generated by the proton pumps.
1) K.Yoshida et al., Nature, 373, 291 (1995).
