Database Product Description
- Host Organism
- Brassica napus (Argentine Canola)
- Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Bayer CropScience (Aventis CropScience(AgrEvo))
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Brassica napus (Argentine Canola) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Argentine or oilseed rape (Brassica napus) was grown as a commercial crop in over 50 countries, with a combined harvest of 48.9 million metric tonnes in 2006. The major producers of rapeseed are China, Canada, India, Germany, France, the United Kingdom and Australia. Canola is a genetic variation of B. napus that was developed through conventional breeding to contain low levels of the natural rapeseed toxins, glucosinolate and erucic acid. Canola is grown for its seed, which represents a major source of edible vegetable oil and is also used in livestock feeds.
The only food use of canola is as a refined oil. Typically, canola oil is used by itself as a salad oil or cooking oil, or blended with other vegetable oils in the manufacture of margarine, shortenings, cooking and salad oils. Canola meal, a byproduct of the oil production process, is added to livestock feed rations. An increasing amount of oil is being used for biodiesel production, especially in Europe.
The removal of weeds early in the growing season is extremely important in canola production. Young canola seedlings are not very competitive and early weed pressure has detrimental effects on final yield. Precautions such as pre-plant tillage or herbicide application are common approaches for reducing weed competition. Once established, canola forms a dense canopy and is very competitive, making weed control less of a concern.
At present, it is expensive, but possible, to control annual grassy weeds (wild oats, volunteer cereals), perennial weeds (Canada thistle, perennial sow thistle, quackgrass), and certain annual broadleaf weeds in canola. The broadleaves are the most difficult to control because there are few herbicide options available. Many producers will use as many as four herbicides per year in an effort to control weeds.
Traditionally, it has been difficult to manage weeds in canola rotations because of the need to use Group 1 herbicides (Assure®, Fusion®, Poast®, Select®, Venture DG®) that are also commonly used to control weeds in flax, wheat and other cereals. Growers favour these herbicides because they are easy to work with, are extremely effective, and may be applied over a period of time. However, the constant use of Group 1 herbicides has placed large acreages of cultivated land at high risk of developing Group 1 weed resistance. The establishment of several herbicide-tolerant weed populations demonstrates this problem.
The canola line T45 was genetically engineered to express tolerance to glufosinate ammonium, the active ingredient in phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically resembles the amino acid glutamate and acts to inhibit an enzyme, called glutamine synthetase, which is involved in the synthesis of glutamine. Essentially, glufosinate acts enough like glutamate, the molecule used by glutamine synthetase to make glutamine, that it blocks the enzyme's usual activity. Glutamine synthetase is also involved in ammonia detoxification. The action of glufosinate results in reduced glutamine levels and a corresponding increase in concentrations of ammonia in plant tissues, leading to cell membrane disruption and cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in T45 is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces viridochromogenes, the same organism from which glufosinate was originally isolated. The PAT enzyme catalyzes the acetylation of phosphinothricin, detoxifying it into an inactive compound. The PAT enzyme is not known to have any toxic properties.
Line HCN28, which was derived from T45, was field tested in Canada (1993 - 1995), in the United States (1996, 1997) and in Chile, Japan, the United Kingdom, and Australia. Agronomic characteristics such as cotyledon width, pod and leaf length, flowering period, time to maturity, plant height, lodging score, seed yield and thousand seed weight were compared to those of unmodified canola. The only significant difference between HCN28 canola and the parental non-transformed variety was its tolerance of glufosinate ammonium. It was demonstrated that the transformed canola line did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. Canola line HCN28 was not expected to impact on threatened or endangered species.
Brassica napus may outcross (up to 30% of the time) with plants of the same species, and potentially with plants of related species B. rapa, B. juncea, B. carinata, B. nigra, Diplotaxis muralis, Raphanus raphanistrum, and Erucastrum gallicum. Previous studies have demonstrated that cross hybridization is most likely to occur with B. rapa. Because of the ability of canola to outcross with related plants, the formation of glufosinate-tolerant hybrids is possible. However, the glufosinate-tolerance trait is not expected to provide a competitive advantage to hybrid plants unless grown in managed environments routinely subjected to glufosinate applications. In the event that a glufosinate-tolerant hybrid survived, the herbicide-tolerant individual could be easily controlled using mechanical and/or other available chemical means.
The human consumption of canola products is limited to the refined oil. Refined edible canola oil consists of purified triglycerides (96-97%) and does not contain any detectable protein, and hence no PAT protein was detected in the refined oil of HCN28 canola. As such, there will be no human exposure to this novel protein as a result of the consumption of refined oil from line HCN28. Compositional analyses of processed canola oil from HCN28 and current commercial canola cultivars were compared for fatty acids, glucosinolates, chlorophyll and phytosterol content. These comparisons indicated no statistically significant differences for the components analyzed. The use of refined oil from HCN28 would therefore have no significant impact on the nutritional quality of the food supply.
Canola meal from line HCN28 was also assessed to determine its safety for use in animal feed. Additional compositional studies were conducted, revealing no significant differences in the moisture, oil, protein, crude fibre, ash, phytosterol and gross energy content between HCN28 and other commercially available canola lines, thus supporting the safety of the inclusion of HCN28 canola in animal feed.
It was determined that there were no toxicity and allergenicity concerns with HCN28. There is no dietary exposure to PAT since this protein is not present in the refined canola oil consumed by humans. PAT was not found to have any amino acid sequence similarities with known toxins or allergens. The PAT enzyme does not possess the proteolytic or heat stability characteristic of toxic compounds, and was readily digested under conditions simulating mammalian digestion. An acute oral toxicity study revealed that no negative effects were experienced by rats fed high doses of the PAT protein (up to 50,000 ppm for a period of 14 days), providing further evidence supporting the lack of toxicity or allergenicity concerns related to the expression of PAT protein in HCN28 canola.
Links to Further Information Expand
This record was last modified on Monday, August 7, 2017