Consequences of Genetic Modifications

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Exogen DNA fragments can be inserted into the DNA of the host organism, mostly the plant, in order to improve productiveness, enhance tolerance to herbicides, or induce production of new substances not present prior to GM (122). In order to improve the quality, in GM food of plant origin, some harmful or allergenic proteins can also be removed (86,123). However, proteins in the living cell are in permanent interaction, and introduction of a foreign gene product, change in concentration or complete removal of another cellular protein can induce complex and possibly unexpected changes in complete cellular proteome (121,124).

The simplest proof of GM in food is the detection of foreign DNA derived from genetically modified organisms (125). The comparison between GM and non-GM crops comprises agronomic and phenotypic characteristics that are very sensitive indices of alterations and also robust indicators of equivalence. Feed performance studies with rapidly growing animals are also sensitive bioassays in the level of nutritional value of GM food (126,127). The GM food has been in use worldwide for over 10 years and until now no verifiable unintended toxic or nutritional effects as a result of consumption of GM products have been registered (128,129). However, the above mentioned complex changes in proteome as a consequence of GM can be detected only by use of proteomics technology. In a very extensive series of studies, Ruebelt et al. (19, 130, 131) compared proteomes of GM and non-GM seeds of the model plant Arabidopsis thaliana. Analytical validation of the method (comparative 2D electrophoresis, 19) and assessments of both natural variability (130, 132) and unintended effects (131) were performed. These studies can be used as fundaments for further quality assessment of GM crops, although faster and more effective methods such as differential in-gel electrophoresis (DIGE) (51), isotope labeling techniques (43), and gel-free, label-free quantitative approaches (82) have recently been developed.

GM crops, especially maize (133), tomato (88) and soybean (95, 134) were the topics of further, intensive proteomic studies. Erny et al. (133) studied alcohol-soluble endosperm proteins, so-called zein proteins from corn of GM and non-GM maize by the use of capillary electrophoresis followed by mass spectrometry. Proteomic fingerprints of different maize lines including the transgenic one were analyzed. Unfortunately, only the analytical method was demonstrated and no further conclusions regarding differences between GM and non-GM seeds were documented. Comparative 2D electrophoresis was used for the analysis of GM and non-GM soybean seeds and eight differently expressed proteins were identified. One of them is Gly m Bd 28k fragment, already known as an allergen (134). Allergens were already identified in GM soybean seeds (95), and further careful monitoring of these foods is still necessary.