By Les Hearn
The debate about genetically modified (GM) foods exploded in August 1998 when research scientist Arpad Pusztai, of the Rowett Research Institute in Aberdeen, announced that GM potatoes harmed experimental rats by making their livers and brains smaller and their spleens larger. A colleague showed that the gut lining was inflamed too.
Responses fell into two categories: Pusztai’s boss and representatives of GM food companies criticised his work as not supporting his claims and Pusztai was suspended and silenced; opponents of GM foods seized on his statements with enthusiasm, forecasting an epidemic of cancer and the virtual destruction of nature. Some critics of Pusztai were subsequently shown to be mistaken and many scientists supported his findings at least as requiring further research. The truth now appears to be that Pusztai’s research does not really prove anything and that much more carefully designed experiments need to be done.
One avenue of development of GM foods involves making plants produce their own pesticides. Some plants, like the snowdrop, produce proteins called lectins: some of which harm insects that eat these plants. Researchers aim to insert genes for lectins into food plants to give them protection without having to spray them with pesticides.
Pusztai decided to feed potatoes with the gene for the snowdrop lectin to young rats to see what effects might be produced. He fed other rats with ordinary potatoes with the lectin added (but not the gene) and still others with potatoes alone (the “control” group). In all, he did four sets of experiments.
Unfortunately, rats do not live by spuds alone and, in three experiments, the rats became malnourished. In these circumstances the weights of body organs fluctuate unpredictably. In the fourth experiment, Pusztai added protein supplements to avoid malnourishment but the potatoes were all raw. Now, raw potatoes are toxic, containing their own lectin, among other unpleasant chemicals: that’s why we don’t eat them raw. Therefore, we cannot conclude anything from this study!
What needs to be done is to test each component of the transferred genetic material, making sure that the food is nourishing and wholesome in every other way. The proposed three year moratorium on the release of genetically modified crops is a useful opportunity for research on this an the other criticisms of GM food.
Why genetically modify foods?
As soon as agriculture was developed, two problems became apparent. First, our delicious food crops are delicious to insects and other pests as well. Second, many grow more vigorously than food crops, using up water and nutrients and spoiling the crop if not removed. The modern approach to these problems is the chemical one: pesticides to kill the pests and herbicides to kill the weeds. Unfortunately there are harmful side-effects to this approach.
Now, some plants produce their own chemical defences to pests; others are resistant to herbicides. By careful breeding, it is sometimes possible to get their properties into food plants. For example, some species of wild potato make their own insecticide. And there is the variety of oilseed rape called “Smart Canola” that is resistant to many herbicides. The crop can be sprayed to kill all weeds without damaging the harvest. It was developed by conventional selection and breeding techniques.
Often, however, breeding does not come up with the solution, perhaps because the desired resistance is not found in plants closely related to the food plant. This is where it is hoped that genetic modification can short-circuit the problem.
The desired genes are removed from a species with the resistance, joined with a promoter gene and other genes to make what is called a “construct” and inserted into the genetic material of the food plant. The promoter’s task is to turn on the resistance genes which would otherwise sit there doing nothing. A common promoter comes from a plant virus called the Cauliflower Mosaic Virus (CMV). The other genes are there as “markers” to tell researchers if the gene transfer has been successful.
What can go wrong?
The presence of the foreign genes can disrupt the normal growth of the plant. In the GM potatoes fed to the young rats, levels of protein and carbohydrate were altered. Since the nutritional value of food crops is closely monitored, this is unlikely to be a problem as substandard varieties would not be grown for crops.
Can the foreign genes get from our food into us? If so, then genes from our food can also get into us and must already have done so. There is no evidence for this (apart from the “couch potato”). It has been suggested that the CMV promoter gene could get into us and perhaps turn on our genes indiscriminately, causing cancer. This, at least, should be investigated, since this was one suggested explanation for the supposed results of the GM potato experiments.
Can the genes escape into the wild? They could only do this to closely related species and this is a good reason for caution until studies have been carried out. However, many crop plants come from other continents and do not have close relatives here.
Can pesticide genes harm beneficial insects? It has been claimed that ladybirds feeding on aphids feeding on GM plants do not grow so well. Others have explained this by showing that the aphids were smaller due to being poisoned by the plant’s insecticide and that ladybirds which ate more of them grew normally. In any case, this would already be happening naturally in plants with those genes.
The other argument often heard is that farmers would use more herbicide on resistant crops and that this would harm the environment by removing food from creatures that lived on the weeds. It is claimed, however, that less herbicide might be needed, with perhaps just one application immediately before harvesting. Either way, this is not an argument exclusive to the question of GM crops.
By Les Hearn