Flavonoid-rich genetically modified rice to boost antioxidant levels?

Rice genetically modified to have high flavonoid content has a 22 per cent higher antioxidant activity than untransformed rice, says a joint German-Indian study.
"The transgenic rice and its derived foods may serve as potential source of antioxidant compounds and this helpful in promoting human health," wrote lead author Ambavaram Reddy in the Elsevier journal Metabolic Engineering.

A number of genetically modified plants and crops are coming to light with enhanced nutritional content considered to offer human health benefits, including zeaxanthin to potato tubers, and the omega-3 fatty acid, eicosapentaeoic acid (EPA), to soybeans, brassica, and stearidonic acid (SDA) in canola crops.

However, no GM crops with potentially enhanced health benefits have been approved for human consumption. Sonsumer acceptance, particularly in Europe and most notably in the UK, continues to be one of the biggest challenges for these crops.

Researchers from Hamburg University and the University of Hyderabad used the "one gene-multiple metabolites" metabolic engineering concept to produce strains of rice that overexpress the anthocyanidin synthase (ANS) enzyme, obtained from a mutant strain of rice Nootripathu.

The ANS enzyme is part of the flavonoid biosynthetic pathway (the path for producing flavonoids in the plant) and catalyses the formation of coloured anthocyanidins from colourless leucoanthocyanidins, thereby serving as a visible marker of the degree of anthocyanidin production.

Interest in flavonoids is growing rapidly and a mounting body of science, including epidemiological, laboratory-based and randomised clinical trials, continues to report the cancer-fighting potential of a number of different flavonoids, such as isoflavones, anthocyanidins and flavonols.

Five different forms of transgenic rice were produced, and named 2T, 5T, 6T, 9T and 10TC. The latter (10TC) was found to contain the highest levels of anthocyanins (2.52 micrograms per milligram) and the flavonol quercetin (1.37 micrograms per milligram), and the lowest proanthocyanidins (0.09 micrograms per milligram), compared to the control rice (0.12, 0.55, and 0.4 micrograms per milligram, respectively).

This strain was also found to have the highest antioxidant activity with 98 per cent of radicals scavenged, compared to 77 per cent for the untransformed plant, measured using the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical assay.

"Our study is a step towards the development of rice that is nutritionally superior to the traditional and high yielding varieties in terms of antioxidant potential," wrote the authors.

"This strategy can be extended to different food crops to promote biofortification with natural products of nutritional value and to other agriculturally important crops for enhanced resistance against biotic and abiotic stresses," they concluded.

Rice is the primary food for more than three billion people around the world.

Source: Metabolic Engineering
Volume 9, Pages 95-111
"Novel transgenic rice overexpressing anthocyanidin synthase accumulates a mixture of flavonoids leading to an increased antioxidant potential"Authos: A.M. Reddy, V.S. Reddy, B.E. Scheffler, U. Wienand, A.R. Reddy