Study on the flower color change by measuring vacuolar pH

蓝色牵牛花的花瓣，三色牵牛花。天蓝，在开花期间从紫红色变成浅蓝色。天蓝花青素主要分布在上表皮和下表皮的液泡中，而不在薄壁组织中。我们用质子选择微电极直接测量活花瓣细胞的ph值。蓝色花蕾的ph值为7.7，紫红色花蕾的ph值为6.7。该研究为花期ph值的增加引起颜色变化提供了明确的证据。为阐明pH的增加机理，分别从紫红色芽、蓝色开放花和紫色凋谢花的花瓣中制备了彩色原生质体，并提供了液泡膜。免疫印迹法检测花蕾和花瓣中均保留H^+- atp酶和H^+-PPase。相反，这些蛋白质在褪色的花瓣中不存在。花蕾和开放花瓣液泡膜囊中依赖于ppi和atp的H^+转运活性几乎相同，而凋谢花瓣中没有H^+转运活性。因此液泡pH值不是由质子泵控制的，而可能与另一种离子输运有关。

The petal of blue morning glory, Ipomoea tricolor cv. heavenly blue, changes its color from purplish red to light blue during blooming. The pigment, heavenly blue anthocyanin, was distributed in the vacuoles of upper and lower epidermis and not in parenchyma. We measured pHv of living petal cell directly using proton selective-microelectrode. The pHv of blue open flower was 7.7 while that of purplish 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 colored protoplasts were prepared from the petals of purplish-red buds, blue open flower and purple faded flower, followed by the vacuolar membrane were provided. By immunoblot technique H^+-ATPase and H^+-PPase retained both in the buds and the open flower petals. In contrast those proteins were absent in faded petals. PPi-and ATP-dependent H^+-transport activities in vacuolar membrane vesicles from the buds and the open flower petals were almost in the same level, although no activities in those from the faded flower petals. Therefore the vacuolar pH was not controlled by proton pumps, but might be concerning with another ion transport.