Flower colour is also influenced by co-pigmantation with colourless flavonoids, metal complexation, glycosylation, acylation, methylation and vacuolar pH. The biosynthetic pathway of the flavonoid pigmants is well established. Unfortunately the rose is deficient of this key enzyme and incapable to synthesize the major blue pigment delphinidin. This is an example of the approaches of the classical breeding techniques have been limited by the constraints of a particular species gene pool. That's the natural reason of rarely to have a single species displaying a full spectrum of coloured varieties. Scientists have been using the one from the petunia to make a blue rose.
Genetic engineering provides the facilities for the gene transfer in plants.
These soil bacterium infect the plant and transfer several of its genes to the infected plant cells, resulting in high rate of plant cell division and the gall formation. This naturally occuring genetransfer system have been exploited by scientists who have disarmed the Agrobacterium by delete their tumorigenic genes and engineered them. These Agrobacterium become widelt used safe vectors for plant transformation. Including electroporation, PEG-meduated and particle gun methods. The transgenic cells, shoots and rooted-shoots are selected.