Arpad Pusztai's experiment at the Rowett Research Institute was designed to identify whether potatoes could be genetically engineered to produce a powerful insecticide and yet still be safe to eat, writes Alison Goddard.
Previous work had shown that a group of proteins called lectins could help plants to resist attacks by insects and nematode worms. Some lectins, such as the kidney bean lectin, are known to damage the small intestine.
Scientists at the Rowett decided to try feeding rats on potatoes that had been genetically engineered to produce the snowdrop lectin. Such a potato was produced by researchers at the University of Durham and the Scottish Crop Research Institute and Rowett scientists fed it to the rats.
The researchers also fed one group of rats with potatoes that had been mixed with the snowdrop lectin.
Three trials took place: two lasting ten days and one lasting 110 days.
At the same time, according to an audit committee set up by the Rowett, separate but similar trials were taking place. Other groups of rats were being fed potatoes that had been mixed with a different lectin, the jack bean lectin.
According to the audit committee, the rats that ate the transgenic potatoes that expressed the snowdrop lectin and those that ate the potatoes mixed with the snowdrop lectin did not suffer any weight loss. But the rats that ate potatoes mixed with the jack bean lectin experienced a "small but significant depression in growth". The result was not very surprising, given that jack bean lectin is a powerful insecticide. "The audit committee is of the opinion that the existing data do not support any suggestion that the consumption by rats of transgenic potatoes expressing snowdrop lectin has an effect on growth, organ development or immune function," it concluded.
But Dr Pusztai and his supporters said that although the rats that ate the potatoes mixed with the snowdrop lectin suffered no ill-effects, those that ate the transgenic potatoes had stunted growth. "Potatoes engineered with snowdrop lectin fed to rats caused highly significant reduction in weight of many organs and impairment of immunological responsiveness," stated a document drafted by concerned scientists last week.
Moreover, in a separate statement, other supporters said "the data contained in the audit report itself showed very clearly that the transgenic snowdrop lectin potato had significant effects on immune system function and this alone is sufficient to vindicate entirely Dr Pusztai's statements. "Neither the results of the genetic modification research nor of the audit have been fully revealed," it concluded.