[img_assist|nid=172|title=|desc=|link=none|align=left|width=100|height=43]Scientists in the UK put 16 lines of three different GM potatoes under a range of stress situations and then studied the quantities of two main groups of secondary, toxic metabolites. They found significant differences. An argument why it is necessary to study GM crops under realistic conditions.
Matthew and his co-workers (2005) modified potatoes with two different GM traits (improved cooking quality, resistance to potato cyst nematode) as well as one that with both traits. These potato lines are part of an ongoing commercial development. The scientists planted more then 70 plants of each of their 16 lines in 2001 and 2002, and put them under different stress conditions: blight (Phytohthora infestans), potato leaf roll virus (PLRV), potato virus Y (PVY), white potato cyst nematode (Globodera pallida) bacterial wet rot (Erwinia carotovora), gnagrene (Phoma foveata), gray field slugs and Budapest slugs (Deroceras reticulatum and Milax budapestensis), drought and mechanical damage. Their findings showed significant concentration differences for both groups of toxic secondary metabolites produced by potatoes, sesquiterpenes and glycoalkaloids (PGA).
Plants can't just move away when local conditions turn bad. They can't fight off insects and other pests. And while plants have developed a number of strategies for protections, they can’t constantly brace themselves against drought, virus infections, pest infestations and herbivores all at the same time just in case any such threat might occur. Instead a lot of plants have developed a range of secondary metabolic pathways and physiological reactions to stress situations, ranging from leave movement, reduced evaporation, release of pheromones to attract predators of pest insects, or the production of toxic substances. The possibility that such reactions and secondary substances are changed in GM crops have been pointed out repeatedly, but are usually not studied in risk assessments.
To understand biological and genetic processes, plants are usually subjected to controlled conditions. Of course it make sense to study plants under such controlled conditions if one wants to study the reactions and processes in detail. If a study on the drought effects were infested with slugs, it would become impossible to determine whether effects are caused by the heat or the slugs, so scientists will keep their laboratories free of pest insects and other influences.
Studies about plant composition or toxicology used for approval procedures are also undertaken under such controlled conditions. This might be a first step to look for fundamental differences in the GM crops, but it is not sufficient. A different approach is needed to assess the adverse effects of GM crops on the environment and human and animal heath because these crops will grow out in the open. They will encounter all kind of weather condition, virus infections and pest infestations. Such events are just normal in agriculture.
To test the safety of GM crops in agricultural it is therefore indispensable that GM crops are tested under such realistic conditions, and not only under controlled conditions which exclude stress. Matthew et al. (2005) clearly demonstrated that the genetic modification of their potatoes can result in significant changes of toxic substances in in tuber tissue. It also showed that there is no clear trend. Some stress situations increased the toxin levels, others reduced it. One might be a danger for human and animal health, while the other might make the plants more susceptible for infections. Matthew et al. (2005) state: "From the result of this study and the limited literature on the subject, it is clear that genetic manipulation of carbohydrate metabolism and pathogen resistance often leads to changes in the profile of plant defence compounds present in the organs of potato plants including the tubers."
For the approval procedure of GM crops this means that GM crops need to be tested under the range of normal and extreme, but anticipated stress conditions. It will not be sufficient to study just one or two stress situations as representative for all kind of stress, because plants react differently to different conditions. This will take time and effort, but by the scientific evidence is to big to be ignored.
Matthews D, Jones H, Gans P, Coates St & Smith LMJ (2005): Toxic secondary metabolite production in genetically modified potatoes in response to stress. Journal of Agricultural and Food Chemistry, 10.1021/jf050589r.