Abstract: The present invention relates generally to the field of plant molecular biology and agents useful in the manipulation of plant physiological or biochemical properties. More particularly, the present invention provides genetic and proteinaceous agents capable of modulating or altering the level of acidity or alkalinity in a cell, group of cells, organelle, part or reproductive portion of a plant. Even more particularly, the present invention contemplates methods and agents for modulating or altering pH levels in the vacuole of a cell, group of cells, organelle, part or reproductive portion of a plant. The present invention further provides genetically altered plants, plant parts, progeny, subsequent generations and reproductive material including flowers or flowering parts having cells exhibiting an altered vacuolar pH compared to a non-genetically altered plant. The present invention still further provides methods for modulating or altering flower color in a plant.