Genetically modified plants are often called "transgenic plants", as they contain one or more transgenes from other organisms, however, this term also includes plants in which the transgene was integrated by naturally occurring processes.
There are two common approaches to genetically engineer plants: Most transgenic plants are generated by the biolistic method (particle gun) or by Agrobacterium tumefaciens mediated transformation.
In the biolistic method, DNA is bound to tiny particles of gold or tungsten which are subsequently "shot" into plant tissue or single plant cells under high pressure. The accelerated particles penetrate both the cell wall and membranes. The DNA separates from the metal and is integrated into the plant genome inside the nucleus. This method has been applied successfully for many cultivated crops, especially monocots like wheat or maize, for which a transformation with the help of Agrobacterium tumefaciens is less suitable. A disadvantage of this procedure is the damage done to the cellular tissue.
Agrobacteria are natural plant parasites, and their natural ability to transfer genes is used for the development of genetically engineered plants. To create a suitable environment for themselves, these Agrobacteria insert their genes into plant hosts, resulting in a proliferation of plant cells near the soil level (crown gall). The genetic information for tumour growth is encoded on a mobile, circular DNA fragment (plasmid). When Agrobacterium infects a plant, it transfers so-called T-DNA to a random site in the plant genome. The bacterial T-DNA is cut out of the bacterial plasmid and replaced with the desired foreign gene. The bacterium is used as a means of transporting foreign genes into plants (vector).This method works especially well for dicotelydenous plants like potatoes, tomatoes, and tobacco. Agrobacteria are less suitable for introducing foreign genes to crops like wheat and maize.
Bt crops contain a gene from Bacillus thuringiensis, which enables them to produce an insecticide inside their cells. Although this insecticide, the Bt toxin, acts highly specific, it has been claimed that some Bt crops damage non-target organisms.
Herbicide-tolerant plants withstand the treatment with a broadly active herbicide, which kills all weeds in the field, leaving only the cultivated GM crop unharmed. In countries with a history of several years of GM cultivation, an increasing number of cases of resistant weeds has been reported.
Future generations of GM plants are intended to be suitable for harsh environments, produce increased amounts of nutrients or even pharmaceutical agents, or are improved for the production of bioenergy and biofuels.
Genetically modified plants can spread the transgene to other plants or – theoretically – even to bacteria. Depending on the transgene, this may pose a threat to the environment by changing the composition of the local ecosystem. Therefore, in most countries environmental studies are required prior to the approval of a GM plants for commercial purposes, and a monitoring plan must be presented to identify potential effects which have not been anticipated prior to the approval.
Little research has been conducted on human and animal health. However, in most countries every GM plant is tested in feeding trials to prove its safety, before it is approved for use and marketing. The project GMO-Safety collects and presents biosafety research on GMOs with more in-depth information on this topic.
In many countries, and especially in the European Union, consumers demand the choice between foods derived from GM plants, conventionally or organically produced plants. This requires a labelling system as well as the reliable separation of GM and non-GM crops at field level and throughout the whole production chain.
Many countries have established labelling regulations and guidelines on coexistence and traceability. Research projects like Co-Extra, SIGMEA and Transcontainer are aimed at investigating improved methods for ensuring coexistence and providing stakeholders the tools required for the implementation of coexistence and traceability.