Social issues and GM crops
Social issues and GM crops

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Social issues and GM crops

3 A key point in the controversy over GM crops: the Pusztai affair

3.1 Pusztai's experiments

Issues of 'fairness' and our obligations to the developing world do not in themselves explain why the issue of GM plants attracts such controversy. This section focuses on an episode in the fraught history of the development of GM foods that had a significant effect on public attitudes in the UK. In particular, we look at the experiments of Arpad Pusztai in the late 1990s at the Rowett Institute near Aberdeen, Scotland. These experiments are of particular interest to us because they reveal a lot about how science is communicated between scientists and to the world at large, and the pitfalls, ill-feelings and confusions that can occasionally emerge in the process. We begin here with an examination of his experiments.

Arpad Pusztai was an expert on a type of plant proteins called lectins. One such lectin, Galanthus nivalis agglutinin, GNA, is found in snowdrops, where it deters sap-sucking insects. GNA is of interest to genetic engineers because, as a natural insecticide, it might be used to introduce insect resistance into a variety of crops. Pusztai was funded to investigate whether the consumption of GM potatoes engineered to produce such lectins would have any effect on the growth and immune system of rats.

Pusztai conducted feeding trials both over a short period of 10 days and also over a longer regimen of 110 days. One experiment involved feeding rats with a diet of raw, baked or boiled potatoes over a 10-day period. A proportion of these potatoes were genetically modified to produce GNA, while some of them had GNA added to the unmodified potatoes. It is not clear from Pusztai's account, whether the modified or adulterated potatoes were supplied raw, baked or boiled. Such small details matter enormously; for instance, prolonged boiling substantially reduces the concentration of GNA. The interpretation of Pusztai's results is further complicated by the fact that a diet of potatoes is nutritionally very poor for rats - so much so that Home Office regulations insist that such diets have to be supplemented by added protein if the feeding regimen is conducted for substantial periods of time. Indeed, Pusztai noticed that the rats fed on unmodified boiled potatoes had a comparatively low rate of growth - and those on unmodified raw potatoes an even lower growth rate.

In one experiment, Pusztai looked for differences between rats fed genetically modified raw potatoes expressing GNA and those fed raw unmodified potatoes. He compared the body mass of these animals after their death with their so called 'empty' body mass, where the food present in the lumen of their guts had been removed by flushing. Pusztai took the view that if there was an atypical difference between these two masses, indicating a larger proportion of the diet had remained undigested in the gut, it would suggest that digestion had been affected by the GM potatoes. He did find an unusual difference of this type in one experiment, though it was not evident in another similar experiment. On the basis of this evidence, Pusztai speculated that 'digestion and absorption of nutrients of transgenic potato diets was retarded in comparison with ordinary potato diets'. But you'll appreciate that for such a statement to be any more than speculation, the diets of the two sets of rats would have to be identical in all respects other than the inclusion of potatoes expressing the GNA gene - if this is not so, the differences in the amount of material in the gut could be due to some other cause. It's known that the transgenic potatoes contained 20% less protein than the non-GM potatoes. Normally the experimental design would allow for such a difference by supplementing the GM diet with extra protein; such adjustments do not seem to have been routinely made in all Pusztai's experiments - certainly not in the short-term feeding experiments.

Pusztai found no statistical difference in the growth rate of rats fed transgenic GNA potatoes over the prolonged 110-day period, compared to the growth rate of a control group fed unmodified potatoes without added GNA. Also rats fed unmodified potatoes spiked with added GNA grew at the same rate as rats fed the same diet without GNA.

From his studies of the immune system of such rats, Pusztai concluded that animals that were fed transgenic potatoes became immunosuppressed. However, the majority view of those appraising Pusztai's data was that such effects are variable and inconsistent and that the effect is not statistically significant. Pusztai went further and claimed that when GNA was simply added to unmodified potatoes, there was no effect on the immune system. This implies that it wasn't the product (GNA) that was causing the problem, but something about the process of genetic modification itself. The 'construct' used to make GM GNA potatoes includes a promoter derived from a plant virus - cauliflower mosaic virus, CaMV. The virus is non-toxic to humans and widely distributed in nature; it is present in broccoli, for example. The CaMV promoter is used in a variety of GM products, so if Pusztai's data were valid, the safety of many GM crops would be under suspicion.

Question 6

How could you test whether the presence of a particular promoter (rather than an adjacent gene or its product) was having an effect on animals eating GM food?


One approach would be to modify potatoes using the same CaMV promoter, alongside another gene, perhaps one that was not functional. Tests would have to be undertaken that such an insertion would make no difference to other nutritional variables in the potatoes, especially protein content. These would be technically demanding and time-consuming procedures.

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