Scientists from the Institute of Plant Biochemistry. Leibniz in Halle, Germany, created purple tomatoes using genetic engineering techniques. To do this, they inserted genes responsible for the biosynthesis of betanin from beets into the tomato plant, and activated them in ripening fruits.
Betanine is not produced by tomato plants; it is extracted from beetroot and used as a natural food coloring.
The main goal of this study was not to create a new variety of tomatoes for human consumption, but to improve the methods of genetic engineering, because in this case the transgenic plants will produce a clearly visible pigment.
Plants are very effective and complex systems with a large number of regulatory mechanisms that, instead of accelerating, are able to slow down the process of biosynthesis of the produced substance. These complex feedback mechanisms are still poorly understood.
Researchers from Halle inserted three genes into the tomato plant that are necessary for the biosynthesis of betanin, as well as several “genetic switches” so that the inserted genes are only active in the fruit during ripening. However, the production of betanin in the fruit was negligible at first.
It was necessary to insert a fourth gene, providing an important precursor substance in order to maintain a higher level of pigment biosynthesis. This is how dark purple tomatoes were born, containing even more betanin than beetroot itself.
The resulting fruits are completely safe for consumption and very useful, since betanin, like many other pigments, has a strong antioxidant effect.
Purple fruits can also be a source of betanin, a food coloring. Early attempts to use tomato betanin to color yoghurts and lemonades have produced interesting and promising results.