Genetically Modified Soybeans: Herbicide Tolerance and Modified Oils
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About 65% of Canadian soybeans are genetically modified, most commonly by the addition of herbicide tolerance (HT) traits. In fact, HT-soybeans are the most commonly grown GE crop worldwide. The biotechnology-assisted development of HT crops is covered in detail in the backgrounder about genetic modification and genetic engineering, so we’ll just briefly review herbicide tolerance here.
Herbicide tolerance is not exclusively biotechnology-driven. There will always be rare genetic mutations in crop plants that result in an HT trait, and it is possible to enhance this naturally occurring tolerance through selective breeding. This process is often inefficient, time-consuming and results in the introgression of extra genes. Genetic engineering for herbicide tolerance involves moving specific genes that confer tolerance from soil bacteria to crop plants. Crops with an HT trait are valuable because they survive the application of a broad-spectrum herbicide (glyphosate or glufosinate ammonium) that kills the competing weeds. The advantages of HT crops include a reduction in tilling as a method of weed control, with the associated environmental benefits of low-till or no-till agriculture, and the switch to newer herbicides with lower toxicity. Glyphosate-resistant soybeans (Monsanto Company) and glufosinate resistant soybeans (Bayer Crop Science) are grown in Canada and approved for food use.
Canadian farmers also grow soybeans with genetically engineered oil content
. A bit of “nutrition 101” is necessary to really appreciate why this is beneficial. Soybeans are 17-21% oil, and this oil is extracted by processing the soybeans in a “crush plant”. Oils and fats are both organic, water-insoluble molecules called lipids
and are an important part of our diets. Oils, like soybean oil, are liquid at room temperature. Fats, like butter, are solid at room temperature.
...an aside about lipids
You’ve probably heard of saturated and unsaturated fat. These terms describe the chemical properties of the fatty acids that are the main components of lipids. If the fatty acid carbon chain has no double bonds it is called saturated, if it has one double bond it is called monounsaturated, and if it has multiple double bonds it is called polyunsaturated. Lipids with a lot of saturated fatty acids are fats (solids) and lipids with a lot of unsaturated fatty acids are oils (liquids).
Some saturated fatty acids are important in our diet, but too many are bad for our cardiovascular health so increasing our consumption of unsaturated fatty acids is desirable. However, oils with a lot of polyunsaturated fatty acids are unstable, which limits their usefulness for high-heat applications like frying, or as ingredients in packaged foods that are expected to have a long shelf life. Soybean oil has a healthy fatty acid profile of 15% saturated, 23% monounsaturated, and 62% polyunsaturated fatty acids, but the high polyunsaturated fatty acid content means that soybean oil is not very heat stable. It can be chemically altered, through a process called hydrogenation, to increase the saturated fatty acid content and improve its stability, but chemical hydrogenation also creates unhealthy “trans” fatty acids.
Monounsaturated fatty acids can be converted to polyunsaturated fatty acids in living things. Biolistic transformation (“gene gun” technology) was used to introduce a piece of DNA that encodes an incomplete version of the plant enzyme responsible for converting monounsaturated to polyunsaturated fatty acids, resulting in silencing of the regular gene. Gene silencing means the enzyme is not expressed, so monounsaturated fatty acids are not readily converted to polyunsaturated fatty acids. This increases the monounsaturated fatty acid content of the soybean oil from 23% to 77%, and decreases the polyunsaturated fatty acid content from 62% to 11%. This modified oil is very stable, so it is useful for frying and as an ingredient in packaged foods. Because it has not been chemically hydrogenated to achieve this stability, it has no unhealthy trans fatty acids. Pioneer Hi-Bred International is the company that currently sells soybean seeds with this trait, marketed under the name Plenish™. In the U.S., Plenish™ soybeans are eligible for IP certification.
Other companies have developed soybean varieties with different oil profiles, either through genetic engineering or conventional crop breeding to select for plants with naturally occurring variations. While several varieties are approved for cultivation and consumption in Canada, none are currently registered as commercial crops.
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