anthocyanin biosynthesis Biosynthesis of anthocyanin compounds. Anthocyanins are water-soluble vacuolar flavonoid pigments that appear red to blue, according to pH. They are synthesized by organisms of the plant kingdom and bacteria. They have been observed to occur in all tissues of higher plants, providing color in leaves, stems, roots, flowers, and fruits. GO:0009718 pathway UPa:UPA00009 flavonoid biosynthesis pigment biosynthesis