Database Product Description
- Host Organism
- Gossypium hirsutum (Cotton)
Herbicide tolerant, oxynil.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for fibre, livestock feed, and human consumption.
- Product Developer
- Calgene Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Gossypium hirsutum (Cotton) Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Cotton (Gossypium hirsutum L.) is primarily grown for its seed bolls that produce fibres used in numerous textile products. The major producers of cotton seed and lint are China, the United States, India, Pakistan, Brazil, Uzbekistan and Turkey.
About two thirds of the harvested cotton crop is seed, which is separated from the lint during ginning. The cotton seed is crushed to produce cottonseed oil, cottonseed cake (meal) and hulls. Cottonseed oil is used primarily as cooking oil, in shortening and salad dressing, and is used extensively in the preparation of snack foods such as crackers, cookies and chips. The meal and hulls are an important protein concentrate for livestock, and may also serve as bedding and fuel. Linters, or fuzz, which are not removed in ginning, are used in felts, upholstery, mattresses, twine, wicks, carpets, surgical cottons, and in industrial products such as rayon, film, shatterproof glass, plastics, sausage skins, lacquers, and cellulose explosives.
Effective weed management is critical to cotton production. The removal of weeds early in the growing season extremely important in cotton production. Young cotton seedlings grow slowly early in the season and are not very competitive. Early weed pressure has detrimental effects on final yield. Weeds can also be detrimental later in the growing season; weeds can interfere with harvesting, and can result in a reduction in lint quality due to trash or staining. Precautions such as pre-plant tillage or herbicide application are common approaches for reducing weed competition, as are multiple herbicide treatments. The broadleaf weeds 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.
The BXN™ cotton line was genetically engineered to express tolerance to oxynil herbicides, including bromoxynil and ioxynil. Oxynil herbicides act by blocking electron flow during the light reaction of photosynthesis, inhibiting cellular respiration in dicotyledonous plants. Oxynil herbicides applied at rates recommended for effective weed control are toxic to conventional cotton varieties. The modified cotton line BXN™ contains the bxn gene for oxynil tolerance, and allows farmers to use oxynil herbicides for weed control in the cultivation of cotton.
The bxn gene was isolated from the bacterium Klebsiella pneumoniae subspecies ozaenae and codes for the enzyme nitrilase, which hydrolyses ioxynil and bromoxynil into non-toxic compounds. The nitrilase encoding gene was introduced into the cotton genome using Agrobacterium-mediated transformation, and the bacterial form of the enzyme expressed in this transgenic cotton line functions the same as that found in monocot plants such as corn, wheat and barley.
Transgenic BXN™ cotton was field tested in the United States at a total of 57 sites in 13 states. Field tests were also conducted in Argentina, Bolivia and South Africa in accordance with national regulatory requirements. Based on data from these trials, it was concluded that the transformed cotton line did not exhibit weedy characteristics, and would not negatively affect beneficial or non-target organisms. The transgenic BXN™ cotton line was not expected to impact on threatened or endangered species.
Cotton plants are primarily self-pollinating, but insects, especially bumblebees and honeybees, also distribute cotton pollen. Cotton can cross-pollinate with compatible species including G. hirsutum (wild or under cultivation), G. barbadense (cultivated Pima cotton), and G. tomentosum. Overall, the probability of gene transfer to wild species in unmanaged ecosystems is low due to the relatively isolated distribution of Gossypium species, different breeding systems, and genome incompatibility. Assuming proximity, synchronicity of flowering and availability of insects, transgenic BXN cotton may freely hybridize with other G. hirsutum varieties.
Human consumption of cotton products is limited to refined cottonseed oil and cellulose from processed linters of cottonseed. Processed linters are essentially pure cellulose, and are subjected to heat and solvent treatment that would be expected to remove and destroy DNA. It is generally accepted that the refined oil does not contain protein as the refining process includes heat, solvent and alkali treatments that would remove and destroy any DNA and protein present. The refined cottonseed oil from the transgenic BXN™ line was tested for the presence of the nitrilase protein, which was undetectable. It was concluded that there was little potential for human dietary exposure to the novel protein expressed in this transgenic cotton line.
Compositional comparison of cottonseed oil, cottonseed and meal from BXN™ cotton was made to the same materials from commercial non-transgenic cotton. Parameters measured included proximate analysis (moisture, crude fat/oil, protein, and ash) of cottonseed meal; fibre analysis (crude fibre, acid detergent, and neutral detergent fibres) of cottonseed; fatty acid composition of refined cottonseed oil; and amino acid profiles of cottonseed meal. No significant differences between the transgenic lines and the traditionally bred lines were observed for any of these parameters. It was also determined that the transgenic BXN™ cotton contained levels of gossypol and cyclopropenoid fatty acids, toxic substances naturally found in cotton, within the normal range of variation reported for conventional cotton cultivars.
Refined cottonseed oil and cellulose from linters are devoid of protein and, given that most allergens are proteins, their consumption is unlikely to result in an allergic reaction. The potential for cottonseed oil or linters from BXN™ cotton to constitute a source of allergens is therefore extremely low. In addition, the nitrilase enzyme does not display the properties of known allergens, such as glycosylation and protease stability. Further, an amino acid sequence comparison did not reveal any homologies between known protein allergens or toxins and the nitrilase enzyme. These data, along with the presence of the nitrilase protein in monocot food sources such as corn and barley, supported the conclusion that the nitrilase enzyme, and thus BXN™ cotton, possessed little or no potential for allergenicity or toxicity.
Links to Further Information Expand
This record was last modified on Friday, March 26, 2010