XVI International Botanical Congess

The blue morning glory, Ipomoea tricolor cv. heavenly blue, changes its petal color from purplish red to light blue during blooming. The pigment, HBA, was only distributed in the vacuoles of epidermis and not in parenchyma. We measured pHv of living petal cell directly using proton selective-microelectrode. The pHv of blue flower was 7.7 while that of red buds was 6.7. This study provides the clear evidence that the color change is caused by the increase of pHv during blooming. To clarify the pH increasing mechanism the vacuolar membrane vesicles were prepared from the colored protoplasts from the petals and the activity of V-ATPase and V-PPase were studied.