1. Why should we evaluate the safety of transgenic plants?
The traditional breeding technology is to create new varieties with higher yield or better quality through intraspecific or interspecific hybridization of related plants, combined with excellent characters. This technology has made great contributions to the rapid development of agricultural production in this century, but its limiting factor is the limited scope of gene exchange, which is difficult to meet the requirements of the sustained and rapid development of agricultural production in 2 1 century. Transgenic plants refer to the use of recombinant DNA technology to introduce cloned excellent target genes into plant cells or tissues and express them in them, so that plants can obtain new characters. This technology overcomes the limitation of sexual hybridization in plants, expands the scope of gene exchange infinitely, and can introduce genes from bacteria, viruses, animals, humans, distant plants and even synthetic genes into plants, and has a very broad application prospect. For example, the glyphosate-resistant gene is transferred to soybean, which makes soybean resistant to this herbicide, thus greatly simplifying the measures to control weeds in soybean. This transgenic soybean was approved by the US Environmental Protection Agency in 1995 and put into field production. By 2000, its planting area had reached 25.8 million hectares, accounting for 36% of the total soybean area in the world.
Theoretically speaking, both transgenic technology and conventional cross breeding obtain new varieties through excellent gene recombination, but the safety of conventional breeding has not been questioned. The main reason is that conventional breeding is carried out by simulating natural phenomena, and the scope of gene recombination and communication is very limited, limited to intraspecific or related species. Moreover, no disastrous results have been found in long-term breeding practice. On the other hand, transgenic technology can transfer any organism or even synthetic genes into plants. Because this kind of event can't happen in nature, people can't predict the effect of transferring genes into a new genetic background, so there are doubts about its consequences. An effective way to eliminate this doubt is to evaluate the safety of transgenic plants. In other words, it is necessary to accumulate enough data through reasonable experimental design and strict scientific experimental procedures. According to these data, people can judge whether the field release or large-scale commercial production of transgenic plants is safe. It has been proved by experiments that safe transgenic plants can be formally used in agricultural production, while transgenic plants with potential safety hazards should be restricted to avoid endangering human survival and destroying the ecological environment. Only in this way can we give full play to the great application potential of transgenic technology in agricultural production.
Second, the main contents of safety evaluation of transgenic plants
At present, the safety evaluation of transgenic plants mainly focuses on two aspects, one is environmental safety, the other is food safety.
(A) the environmental safety of genetically modified plants
The core question to be answered in environmental safety assessment is whether releasing transgenic plants into the field will transfer genes to wild plants, or whether it will destroy the natural ecological environment and break the dynamic balance of the original biological population.
Possibility of transgenic plants evolving into weeds in farmland: whether plants will increase their survival competitiveness after obtaining new genes, and whether they are stronger than non-transgenic plants in growth potential, overwintering, seed yield and viability. If transgenic plants can survive in natural ecological conditions, it will inevitably change the natural biological population and break the ecological balance. From the field test results of transgenic plants such as rice, corn, cotton, potato, flax and asparagus, the growth potential and wintering ability of transgenic plants are not stronger than those of non-transgenic plants, which means that the survival competitiveness of most transgenic plants has not increased, so they generally will not evolve into farmland weeds.
Possibility of gene drift to related wild species: under natural ecological conditions, some cultivated plants will naturally cross with related wild species growing around them. So as to transfer genes from cultivated plants to wild species. If transgenic plants are planted in these areas, the transferred genes can drift into wild species and spread among wild relatives. When evaluating the safety of transgenic plants, we should consider this problem from two aspects. One is whether there are related wild species that can be hybridized with transgenic plants in the release area. If not, gene drift will not happen. If transgenic cotton is planted in Canada, gene transfer is impossible because there are no related wild species. Similarly, in China, without weeds, there would be no gene drift. There is also a possibility that there is a related wild species, and genes can be transferred from cultivated plants to wild species. At this time, it is necessary to analyze and consider the effect after gene transfer. If it is a herbicide-resistant gene, it will make wild weeds resistant after gene drift, thus increasing the difficulty of weed control. Especially, if multiple herbicide-resistant genes are simultaneously transferred into a wild species, it will bring disaster. However, if the quality-related genes are transferred into wild species, it will have little impact because it cannot increase the survival competitiveness of wild species.
Effects on natural biological groups: Many genes used in plant genetic engineering are related to insect resistance or disease resistance, and their direct targets are organisms. For example, the target insects of transgenic Bt cotton are plant pests such as cotton bollworm and red bollworm. If it is used in a large area for a long time, insects may have adaptability or resistance to insect-resistant cotton, which will not only affect the application of insect-resistant cotton, but also affect the insect-resistant effect of Bt pesticide preparation. In order to solve this problem, when promoting insect-resistant cotton, it is generally required to plant a certain proportion of non-insect-resistant cotton to delay insect resistance. In addition to target insects, we should also consider the influence of transgenic plants on non-target insects. If someone feeds six kinds of non-target insects in cotton field with Bt protein feed, when the concentration of insecticidal protein is 100 times higher than that of the control target insect, there is no visible growth inhibition on the non-target insects. In addition, Bt protein is not toxic to beneficial insects such as bees and ladybugs.
(2) Food safety of transgenic plants
Food safety is also an important aspect of safety evaluation of transgenic plants. OECD 1993 put forward the principle of substantial equivalence in food safety evaluation. If the products produced by transgenic plants are basically equivalent to traditional products, they can be considered safe. For example, antiviral plants with virus coat protein gene and their products and products produced by plants infected with virus in the field all carry coat protein, and such products should be considered safe. If the products produced by transgenic plants are essentially different from traditional products, strict safety evaluation should be carried out. When evaluating substantive equality, the following main aspects need to be considered.
Toxic substances. It is necessary to ensure that the transferred foreign genes or gene products are non-toxic to humans and animals. For example, transgenic Bt corn contains Bt insecticidal protein, which is basically equivalent to traditional corn in nutritional composition. To evaluate its safety as feed or food, we should focus on the safety of Bt protein to people and animals. At present, a large number of experimental data prove that Bt protein is only toxic to a few target insects and absolutely safe to humans and animals.
Allergen. There are many allergens in natural conditions. In genetic engineering, if the genes that control the formation of allergens are transferred to new plants, it will have adverse effects on allergic people. Therefore, plants transformed with allergen genes cannot be approved for commercialization. For example, some people in the United States transferred the 2S albumin gene of Brazil nuts to soybeans, which increased the sulfur-containing amino acids in soybeans, but it was not approved for commercial production. In addition, the contents of nutrients and anti-nutritional factors should also be considered.
Third, transgenic plants at home and abroad
General situation of safety evaluation
(A) Safety evaluation of foreign transgenic plants
Major developed countries and some developing countries in the world have formulated their own regulations on the management of genetically modified organisms (including plants), which are responsible for evaluating and monitoring their safety. For example, in the United States, the content of genetic modification has been added on the basis of the original federal law, and the Animal and Plant Quarantine Bureau of the Ministry of Agriculture, the Environmental Protection Agency and the Federal Food and Drug Administration of the United States are responsible for the environmental and food safety assessment and approval respectively. Due to the great differences in laws and regulations among countries, especially many developing countries have not yet established corresponding laws and regulations, some international organizations such as OECD and United Nations Industrial Development Organization (U? NIDO), FAO and WHO have organized many expert meetings in recent years, actively organized international coordination, and tried to establish unified management standards and procedures for biotechnology industry acceptable to most countries (especially developing countries). However, due to many disputes, no unified regulations have yet been formed.
Generally speaking, the management of genetically modified plants in the United States and Canada is relatively loose. In 2000, the United States planted 30.3 million hectares of genetically modified crops, accounting for 70% of the world's genetically modified crops. If Canada and Argentina are added, these three countries account for 98% of the global genetically modified crops. In sharp contrast, European countries. From the research perspective, European countries, especially Britain, France and Germany, have carried out extensive and in-depth research in the field of agricultural biotechnology and developed a number of genetically modified crops that can be used for production. But until now, few genetically modified crops have been planted as commodities in Europe. It is difficult for European consumers to accept genetically modified foods.
(2) Safety evaluation of transgenic plants in China.
The State Science and Technology Commission issued the Measures for the Safety Management of Genetic Engineering in February 1993. According to this principle, the Ministry of Agriculture promulgated the Implementation Measures for Safety Management of Agricultural Biogenetic Engineering in July 1996. According to the provisions of the "Implementation Measures", the Ministry of Agriculture established the Safety Management Office of Agricultural Biogenetic Engineering and the Safety Committee of Agricultural Biogenetic Engineering, which is responsible for the safety evaluation of pilot test, environmental release and commercial production of agricultural bio-genetic engineering bodies and their products nationwide. Since 1997, the safety committee of the Ministry of Agriculture has accepted applications twice a year. Up to last year, the Ministry of Agriculture accepted more than 200 applications in 8 batches, and approved the commercial production of Bt transgenic insect-resistant cotton, tomato with antisense RNA technology, Petunia discolor, antiviral sweet pepper and tomato.