Transgenic Oilseed Rape line unexpectedly increases growth of crop pest
What are the implications for GM food safety testing?
(the address of this page is www.btinternet.com/~nlpwessex/Documents/gmcroppestproblem.htm )
Contrary to some of the claims made about its 'precision', trying to create targeted 'benefits' from genetically modified crops is essentially a 'hit-and-miss' affair (for more on this see www.btinternet.com/~nlpwessex/Documents/oecdgmbrief.htm ). Usually getting the transgenic plant to generate the perceived relevant protein(s) is the first major challenge to be overcome. However, if and when the relevant protein has been generated, the ultimate effects from its production may not be as anticipated.
In this case (see details below) a line of oilseed rape was genetically engineered to produce a protein considered to be toxic to an insect pest. However, in practice, far from killing the pest the new protein actually resulted in the larvae of the insect growing larger.
Because this growth suggests that the larvae were driven to eat more plant material as a result of the generation of the new protein in the rape on which they were feeding, the study concludes that the genetic modification "could be counterproductive as the transformed genotypes would suffer more damage than the untransformed plants" (i.e the genetic modification would increase, not reduce, crop losses from the pest).
One of the reasons that this experiment seems to have produced unexpectedly disadvantageous results is because the genetic engineers (despite their expectations in the matter prior to the trial) did not know enough about the biology of the target pest, specifically the functioning of its digestive system in relation to the protein concerned.
This situation would appear to clearly demonstrate what a 'suck-it-and-see' business the genetic modification of plants is when trying to anticipate the 'downstream' biological effects of any new proteins generated by them.
This profound scientific deficiency has implications well beyond the scope of this study, including the generation of possible unexpected effects from novel proteins in transgenic plants subsequently consumed by humans (for more information on this type of effect see the work of Professor Arpad Pusztai - work which the UK government is refusing to repeat despite a call to do so from the Royal Society, despite its existing publication in the Lancet, and despite the government's own funding of the original study).
This situation is particularly critical when much of the so-called safety tests carried out on GM foods are freqently based on indirect experimental data. The first comprehensive independent food safety testing ever done on a GM plant was the work by Dr Pusztai on transgenic potatoes - and that work was rapidly crushed in a highly orchestrated fashion (according to Dr Pusztai this work demonstrated damaging effects on laboratory rats from a gene which was believed from the outset by the plant breeders to produce no mamalian toxic impact).
Nonetheless the little reported-on study on transgenic oilseed rape below (which produced the opposite affect to what had been expected by the authors when extrapolating findings from other research) has not been subject to organised attempts to discredit it. The study was part-funded by the UK government and carried out jointly by scientists at the Institute of Arable Crop Research (IACR) and the National Institute of Agronomic Research (INRA) in France.
More recently in a comment column entitled "To grow or not to grow" Farming News (25 May 2000) highlighted the importance of consumer concerns over such biosafety issues, particularly those relating to any unintended and poorly understood consequences of altering the nutritional content of food using genetic modification. As Farming News pointed out: "An example of this is Monsanto's introduction of genes into oilseed rape to increase carotenoid levels. The introduction resulted in an unintened and unexplained reduction in tocopherol (including Vitamin E) and a change to the fatty acid composition of the plant.... In this climate British farmers are unlikely to voluntarily grow GM crops....."
Natural Law Party Wessex
12 June 2000
Journal of Insect Physiology 44 (1998) 263 - 270
"Growth stimulation of beetle larvae reared on a transgenic oilseed rape expressing a cysteine proteinase inhibitor"
Cecile Girard, Martine Le Metayer, Bruno Zaccomer, Elspeth Bartlet, Ingrid Williams, Michel Bonade-Bottino, Minh-Ha Pham-Delegue, Lise Jouanin.
Abstract
The resistance of a transgenic line of oilseed rape expressing constitutively the cysteine proteinase inhibitor oryzacystatin I (OCI) was assessed against Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae). The levels of OCI expression in the transformed line averaged 0.2%- and 0.05% of total soluble protein in leaves and petioles respectively. In vitro analyses showed that P.chrysocephala larvae use both cysteine and serine proteinases for protein digestion, and that all the cysteine proteolytic activity is OCI-sensitive. However, bioassays showed that adults fed identically on leaf discs from control or transformed plants. When larvae were reared on transgenic plants expressing OCI, they showed an increase in weight gain compared to those reared on control plants. Furthermore, those larvae from transgenic plants exhibited a 2-fold increase in both cysieine and serine proteolytic activity as a reponse to the presence of OCI. The plasticity of insect digestive physiology and feeding behaviour are discussed, as well as the relevance of engineering a genotype expressing both types of proteinase inhibitors.
[Extracts from main text of paper]
"The potential use of proteinase inhibitor gene sequences to create transformed plants resistant to insect pests has been demonstrated (Hilder et al., 1987; Johnson et al., 1989; McManus et al., 1994; Leple et al.,1995; Duan, et al., 1996). Proteinase inhibitors bind specifically to target gut proteinases and thus inhibit the ability of the insect to digest proteins, which may result in reduced growth rate and death (Broadway and Duffey, 1986a)....
Oilseed rape (Brossica napus L.), a crop of worldwide importance, is attacked by many species of Coleoptera....
Transgenic oilseed rape lines expressing OCI have been produced (Bonade-Bottino, 1993), as part of a programme to develop insect resistant lines of oilseed rape.
The cabbage stem flea beetle (Psylliodes chrysocephala L) is a major pest of winter oilseed rape in Europe (Lamb,1989)...
The aim of this paper was to investigate the effects of OCI expression in oilseed rape on adult feeding, larval growth and digestive physiology of P.chrysocphalia...
Results from this study not only showed that the transgenic line accumulated moderate levels of OCI, but that the protein was processed correctly and was biologically active....
The resistance of a transgenic line expressing OCI was evaluated against P.chrysocephala adults and larvae...
In dual choice bioassays the [adult] insects fed similarly on transgenic and control leaf discs during the 48 hours duration of the experiment...
...this species depends on cysteine and serine proteinases for protein digestion, as previously reported for other coleopteran insects..... Therefore, deleterious effects were expected for larvae reared on the OCI expressing line. Surprisingly, those larvae showed an increased weight gain compared to control larvae [*]. There was almost no effect on larval mortality. Moreover, a 2-fold increase in both cysteine and serine proteinase activities was measured....
The consumption of plant tissue by larvae could not be assessed, but the increased growth rate of the insects fed on transgenic plants could result from an increase in the consumption of plant tissue, possibly to compensate for the overproduction of digestive proteinases. This would be consistent with a previous study showing that Soybean trypsin inhibitor in (SBTI) in wheat sap stimulated feeding and growth rates of the adult grasshoper, Melanoplus sanguinipes, and induced a 6-fold increase in chymotrypsin activity (Hinks and Hupka, 1995).
In the present study P.chrysocephala larvae were able to feed ad libitum on the plants, and may have increased food intake to meet nutritional requirements of digestive enzyme overproduction and increased larval development...
In this case the expression of PIs [proteinase inhibitors] could be counterproductive as the transformed genotypes would suffer more damage than the untransformed plants.....
Long-term impact of proteinase inhibitor consumption requires further investigation to broaden our understanding of the mode of action of proteinase inhibitors in insects. Recently, the ability of larvae of different species to overcome chronic exposure to dietary proteinase inhibitors has been reported....."
* [The weights of all the larvae on control plants were between 0.2mg and 1mg, whereas the majority of larvae on the transgenic plants had a weight between 1.1 mg and 1.7 mg].
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