Rape loses bitter substances

Genetically modified varieties with 80 percent less sinapine

Oilseed rape (Brassica napus) Institute of Plant Biochemistry
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Scientists have genetically modified oilseed rape in such a way that the bitterness synthesis in its seeds is reduced by about 80 percent. The research may help to make rapeseed a source of protein for human food.

Rapeseed is a plant with much underestimated potential. In addition to the already used oil fraction, their seeds contain a lot of protein, which is rich in rare amino acids. After squeezing the seeds, a rich remnant that could be used as a food supplement is produced. At present, the press residue is fed as an additional source of protein to pigs, cattle and chickens.

However, over-consumption of the high-protein diet causes ruminants to suffer from digestive problems, and the eggs of such fed laying hens have a fishy odor and taste. The reason for this is the typical phenolic ingredients for cruciferous vegetables, such as Sinapin, which accumulates mainly in the seed of the plant. These substances also cause the press residue and flour of the seeds to taste bitter and darken by oxidation. Thus, this protein source is unusable for human food.

Researchers switch off genes

This is exactly where the joint project "NAPUS 2000 - healthy food from transgenic rapeseed" began a few years ago: "One idea of ​​the NAPUS project was to produce transgenic plants in whose seeds the synthesis of bitter substances is reduced or blocked" explains Carsten Milkowski, scientist at the Leibniz Institute of Plant Biochemistry (IPB) in Halle. The enzymes involved in sinapine biosynthesis have been known for a long time.

"Knowing a synthetic enzyme and its effect is an absolute prerequisite, but to turn off the genes, you need the DNA sequence, the gene itself, " says Milkowski, describing the problem he was facing. For a genetic modification of the plants, therefore, the genes coding for the synthesis enzymes had to be isolated from oilseed rape. "Together with three other scientists, it took us two years to isolate and functionally characterize the genes of the two key synthetic enzymes, " states Milkowski. display

The introduction of the genes into the rape plants (transformation) was then carried out by other NAPUS partners, the resistance laboratory of the German Seed Union and scientists of the University of Göttingen.

80 percent less sinapine

According to the results, the sinapin content in the seeds could be reduced by 80 percent through the transformation. Examining the properties of transgenic plants in the field will now take place as part of the "YelLowSin Rapeseed" project in Canada.

"Our first task is to reduce the residual content of 20 percent sinapine in the already transformed rape plants to an absolute minimum, " explains Milkowski. This is to be achieved by additionally introducing a bacterial gene into the transgenic rape plant. The gene codes for an enzyme that converts an important component of sinapine into another substance, rendering it unavailable for the synthesis of the bitter end product.

If this strategy were successful, instead of sinapine, another substance that accumulates glycine betaine in the seeds would be. Glycine betaine protects plants from cold and salt stress, but otherwise has no negative impact on their metabolism. "On the one hand, by reducing the enzymes involved and, in addition, removing the required starting materials from the synthetic route, we hope to completely eliminate bitterness synthesis in the seed, " concludes Milkowski.

(idw - Institute of Plant Biochemistry, 21.03.2006 - DLO)