Database Product Description
- Host Organism
- Zea mays (Maize)
- Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Microparticle bombardment of plant cells or tissue
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Dekalb Genetics Corporation
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Zea mays (Maize) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Maize (Zea mays L.), or corn, is grown primarily for its kernel, which is largely refined into products used in a wide range of food, medical, and industrial goods.
Only a small amount of whole maize kernel is consumed by humans. Maize oil is extracted from the germ of the maize kernel and maize is also a raw material in the manufacture of starch. A complex refining process converts the majority of this starch into sweeteners, syrups and fermentation products, including ethanol. Refined maize products, sweeteners, starch, and oil are abundant in processed foods such as breakfast cereals, dairy goods, and chewing gum.
In the United States and Canada maize is typically used as animal feed, with roughly 70% of the crop fed to livestock, although an increasing amount is being used for the production od ethanol. The entire maize plant, the kernels, and several refined products such as glutens and steep liquor, are used in animal feeds. Silage made from the whole maize plant makes up 10-12% of the annual corn acreage, and is a major ruminant feedstuff. Livestock that feed on maize include cattle, pigs, poultry, sheep, goats, fish and companion animals.
Industrial uses for maize products include recycled paper, paints, cosmetics, pharmaceuticals and car parts.
The maize line DLL25 (synonym B16) 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 this maize line is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces hygroscopicus, 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. The PAT encoding gene (bar) was introduced into the soybean genome by micro-particle acceleration (biolistic) transformation, and the resulting maize line displayed field tolerance to phosphinothricin-containing herbicides, thereby permitting farmers to use this herbicide for weed control in maize cultivation.
The maize line DLL25 was field tested in the major maize growing regions of the United States starting in 1991, in Canada beginning 1994, and in Argentina. DLL25 has been evaluated extensively in the laboratory and greenhouse, and in field experiments. The transgenic maize was compared to its non-transgenic counterparts, assessing agronomic characteristics such as vegetative vigour, flowering period, time to maturity, seed production, and disease and insect susceptibilities. Field data determined that the values observed for DLL25 maize were within the normal range of expression currently displayed by commercial maize hybrids. Overall the field data reports and data on agronomic traits showed that maize line DLL25 did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. DLL25 was not expected to impact on threatened or endangered species.
Maize does not have any closely related species growing in the wild in the continental United States and Canada. Cultivated maize can naturally cross with annual teosinte (Zea mays ssp. mexicana) when grown in close proximity, however, these wild maize relatives are native to Central America and are not naturalized in North America. Additionally, reproductive and growth characteristics were unchanged in DLL25. Gene exchange between DLL25 and maize relatives was determined to be negligible in managed ecosystems, with no potential for transfer to wild species in Canada and the United States.
In an assessment of food and livestock feed safety forage and grain from DLL25 maize hybrids were analyzed for nutritional composition and compared to the nutritional composition of non-transgenic versions of the same maize hybrids. Proximate and amino acid analyses were performed. Small differences between DLL25 plants and their non-transgenic counterparts were occasionally observed. However, the nutrient composition of DLL25 maize fell within the range of variability for the relevant nutrients reported for maize. The use of maize products derived from DLL25 was not anticipated to have any significant impact on the nutritional quality of the food supply.
Potential toxicity and allergenicity of the PAT protein expressed in the transgenic maize line DLL25 was investigated by searching for amino acid sequence homology with known toxins and allergens, by examining its physiochemical properties, and by acute oral toxicity testing in mice. No homologies between the deduced amino acid sequence of the PAT protein and the sequences of known toxins or allergens were detected. The PAT enzyme does not possess the proteolytic or heat stability characteristic of toxic compounds, and was readily digested under conditions simulating mammalian digestion. In the acute mouse toxicity study, mice were fed high doses of the PAT protein, with no observable adverse effects. Based on these properties, it was concluded that the PAT protein, and thus DLL25 maize, possessed little or no potential for allergenicity or toxicity.
Links to Further Information Expand
This record was last modified on Friday, March 26, 2010