Abstract
The reddish-purple buds of the wild-type Ipomoea nil change into blue open-flowers. The color change is caused by vacuolar alkalization in the epidermal cells of the flowers. Although InNHX1 for Na+/H+ antiporter was thought to be a major gene responsible for the vacuolar alkalization, a mutant deficient in InNHX1 still shows partial increase the vacuolar pH and its reddish-purple buds become purple open flowers. We identified a novel gene for Na+/H+ antiporter, InNHX2, the deduced amino acid sequence of which showed 71% identity to that of InNHX1. Spatial and temporal expression of these genes and their response to NaCl treatment indicate that InNHX1 appears to be evolved specifically for blue coloration during flower-openning whereas InNHX2 is likely to perform dual functions: promote partial vacuolar alkalization in the petals and to confer salt tolerance on the plant. We will discuss the roles of InNHX1 and InNHX2 for blue flower coloration.
