Function of ItNHX1 During Flower Opening in Blue Morning Glory

Abstract

Petal color of morning glory, Ipomoea tricolor cv. Heavenly Blue, changes from reddish-purple to blue during flower-opening period. The color change is caused by an unusual vacuolar pH increase from 6.6 to 7.7 in the epidermal colored cells. We have already clarified the involvement of ItNHX1 in the pHv increase. To clarify the mechanism and function of ItNHX1 in morning glory petals we studied cellular differences between the red and blue parts in chimera petals in which red parts appeared in the blue colored petal. Anthocyanin components in both blue and red parts were the same HBA. The pHv of red cells measured by a pH-sensitive microelectrode was 6.9 being significantly different from that of blue cells. K⁺ content in red cells was lower than that in blue cells. The function of ItNHX1 in petal color change and cell enlargement will be discussed.