- Martin Hajduch
Gene Experiment Center, University of Tsukuba, Tsukuba, Ibaraki, 305, Japan
Institute of Plant Genetics, Slovak Academy of Sciences, Akademicka 2, P.O.Box 39A, 950 07 Nitra, Slovakia
Like any new or exotic species we do not know the effect of putting these transgenic plants into nature, but we should be sure, that the use of transformed plants in agriculture is safe and have no unexpected influence on the environment. Cordle et al. (1991) have described a step-by-step safety assessment as given below.
A) At first we should determine the level of safety concern for the unmodified organism. This includes the following:
1) the pest/pathogen status of the organism,
2) its ability to become established in the accessible environment,
3) its ecological interrelationship, function and importance in the community,
4) its ability to transfer genetic information,
5) the potential for monitoring and control.
B) As a second step we should consider how the genetics affect safety. This includes the following:
1) the process of genetic modification,
2) gene construction and expression,
3) the degree to which knowledge of molecular biology and other information is available to predict the safety level of modified organism relative to that of the unmodified organism.
C) The third step is to combine the evaluation in steps above. The risk assessment concerning genetically modified organisms (GMOs) is made by integration of the information on the unmodified organism and on the genetic modification.
It is important to have well defined foreign DNA inserts in the transformed plant. By use of available transformation methods it is still difficult to obtain a transformed individual species containing single or low-copy number of foreign genes. Lebel et al. (1995) described a set of broad-host range transformation vector based on the Ac/Ds transposable elements that improve both transformation efficiency and the quality of transgenic loci. This type of vector could be an important additional tool for the production of transgenic plants with well defined foreign DNA inserts required for biosafety approval and commercialization. Determination of possibilities of genes movement from transgenic plants to surroundings is important. Gene escape from transgenic plants can be precipitated by one of several events (Love, 1994):
1) transfer of modified genes into micro-organisms or pathogen population,
2) horizontal movement of genes into other plant species, due to latent infection with a bacterial vector ,
3) escape and proliferation of transgenic plants in to the wild ,
4) hybridization with and transgene introduction into native wild species (Evenhuis et al., 1991; Kapteijns, 1993; Regal,1994).
No evidence exists for gene transfer from plants into microorganisms or for horizontal gene movement, although research will probably continue to provide new information on these issues (Evenhuis et al. 1991). Escape through crop naturalization and escape through hybridization can be much more a problem. In the case of potatoes in the United States and Canada, escape and proliferation of transgenic varieties is not of concern, because potatoes are not competitive outside of cultivated areas. This agree with the conclusion of Bartsch et al.(1993), who determined that a number of crop species have the ability to "run wild", but that potatoes are not among them. Potatoes will neither hybridize with non-tuberous Solanum weed species, nor tuber-bearing Solanum species, because there are a number of barriers which prevent natural hybridization and introgression including endosperm imbalances, multiple ploidy levels, and incompatibility. The number and magnitude of the barriers makes natural hybridization highly unlikely and transgene introgression impossible or at least highly improbable (Love, 1994). Evenhuis and Kapteijns concluded there was no risk in the Netherlands for transgenes to flow from cultivated potato to wild species. The major criterion for this conclusion was the lack of indigenous crossable species. The situation in Slovakia is similar to that found in the Netherlands. This information will have important implications for transgenic potatoes in the future. It should allow the removal of one major concern from the list of regulatory criteria, that of deleterious ecological impact.
Umbeck et al.(1991) made the investigation to determine the movement of pollen from field test site of genetically engineered cotton. The results from this investigation showed a consistent and significant reduction in pollen dissemination as distance from the test plot increased. Conner and colleagues (Tynan et al.1990; Conner et al. 1991) planted fertile chlorosulfuron-resistant potato plants cvs Ilam Hardy, Iwa and Rua on plots surrounded for 10.5m by border rows of nontransformed fertile potato cultivars, or the solanaceous weed, nightshade (Solanum nigra). In the field tests conducted for three subsequent years, they detected only 29 chlorosulfuron-resistant seedlings out of 366500 (0.008%). One of these seedlings was found 6m distant from the test plot, all others were within 4.5m of the test plot. No transgenic progeny were detected in the nightshade plot. Thus, there is no evidence of widespread dispersal of transgenic potato germplasm, and a border row of 6m is sufficient to reasonably ensure containment. The hybridization of transformed plant species with wild flora and ability of the crop to run wild is one way for gene movement also. Field-tests with safe crops can be used to assess the effects of introducing transformed plants in agricultural ecosystem. These aspects have been investigated by Kapteijns (1993) with use of four unmodified agricultural crops (potato, beet, oilseed rape and maize). The toxicity of genes products to humans and animals that have been incorporated into the plant genome require a consideration of each gene construct. Transgenic products that naturally occur in other organisms have been consumed without detriment for years and therefore are undoubtedly safe. This will also be true of the transgenic potatoes that are being engineered either to over-express or under-express potato genes that have been isolated (granule-bound starch synthase, patatin, starch phosphorylase).
A class of molecular aids essential in enabling the genetic construction of transgenic plants - selectable marker genes (e.g. NTP II) and their encoded proteins - stays with the crop and with food made from them. Regulatory committees worldwide are currently debating the safety of these markers. There are four major questions that should be addressed in the safety appraisal: (1) is the NTP II gene product toxic, (2) does eating the NPTII protein compromise oral antibiotic therapy, (3) does the transfer of the NPTII gene from plant to pathogenic bacteria compromise antibiotic therapy.
None of the plant, bacterial and other species into which active NPTII gene has been inserted have shown deleterious effects that could be attributed to the NPTII protein. Calgene (1990) established that NPTII is rapidly inactivated and degraded upon ingestion. Furthermore, in gene therapy cells containing the NPTII gene have been infused into human cancer patients and now adverse effects attributable to NPTII were observed.
Firstly NPTII as a protein which does not contain any unusual amino acids is rapidly inactivated and degraded during the digestive process. Secondly, NPTII requires ATP in order to catalyze the inactivation of kanamycin. ATP is however present in the digestive system at extremely low concentrations. Thirdly, only about 0.36% of the kanamycin administered was for oral or gastrointestinal tract use.
The highest concentration of potentially pathogenic bacteria occurs in the gut. Most, if not all, of ingested NPTII DNA would however, be degraded in the stomach and the small intestine, before it reached the gut. Calgene calculated even with the most liberal assumptions, that eating genetically modified tomatoes containing the NPTII gene, would increase the number of kanamycin - resistant microbes in the gut by less than 0.000001%. We can conclude that there are no scientific reasons to prohibit or limit the use of selectable marker NPTII, nor to encourage or require their removal from genetically modified plants. However, case by case examination of each gene will be necessary before broad use in agriculture is admissible.
As Harada (1996) in his paper has said, for the commercialization of transgenic plants in agricultural system we need to: (1) establish an efficient transformation system, (2) isolate more useful genes, (3) control gene expression, (4) determine the influence of transgenic species on the environment and their quality as food, (5) have public acceptance.
He notes one of the barriers for utilization of transgenic plants in breeding is lack of public acceptance. For the purpose of obtaining public acceptance, first we have to be sure about the safety of using transgenic species. Then we should create an ethical basis for use, which will help us to communicate with the public.
An example how to apply ethical theories into transgenesis is Mepham (1993), who explores a scheme for the ethical evaluation of animal transgenesis beginning with an overview of deontological and consequentialist ethical theories. He proceeds to apply the four ethical principles (autonomy, justice, non-maleficence and beneficence) to the interests of treated animals and of different groups of people affected by biotechnology. He suggested that attempts to eradicate hunger, to improve animal welfare and to devise sustainable agricultural systems will be facilitated by greater investment in the emerging academic field of agricultural bioethics.
The authors would like to express their sincere thanks to Mr. Henry Osador Aigbedo for his irreplaceable help.
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Calgene, Inc. 1990. Request for advisory opinion-kanr gene: safety and use in the production of genetically engineered plants. FDA Docket Number 90A-0416.
Cordle M.K., et al. 1991. Regulation and oversight of biotechnological applications for agriculture and forestry. In L.R. Ginzburg (Ed.) Assessing ecological risks of biotechnology. p. 289-311. Butterworth-Heinemann, Boston
Evenhuis, A. & Zadoks, JC. 1991. Possible hazards to wild plants of growing transgenic plants. A contributtion to risk analysis. Euphytica 55: 81-84.
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Umbeck, P.F., et al. 1991. Degree of pollen dispersal by insects from a field test of genetically engineered cotton. Journal of Economic Entomology 84 (6): 1943-1950.