Database Product Description
- Host Organism
- Beta vulgaris (Sugar Beet)
- Trade Name
- Glyphosate herbicide tolerance.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption.
- Product Developer
- Novartis Seeds; Monsanto Company
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Beta vulgaris (Sugar Beet) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Sugar beet is a botanical variety of B. vulgaris ssp. vulgaris, as are other comestible and fodder beets, and is a member of the goosefoot (Chenopodiaceae) family. It is an important source of sugar (sucrose), accounting for approximately 40 percent of global production.
Sucrose is present in limited quantities in many plants, including various palms and the sugar maple, but sugar beet and sugarcane are the only commercially important sources. More than half of the world sugar supply is obtained from sugarcane, which is grown in tropical and subtropical climates. The rest is supplied by the sugar beet, which is grown in temperate countries. Sugar is manufactured from the roots of the sugar beet; the leaves and tops are removed after harvesting and used as livestock feed. The roots are cut into cossettes, or chips, from which the juice is extracted. The juice is then processed to yield sugar and beet molasses. The pulp remaining after the extraction of the juice is a rich feed for domestic animals. Beet molasses is also fed to livestock; no table molasses is made from beets because of difficulties in purification. The sugar that is produced from the sugar beet is identical to the sugar that is derived from sugarcane.
Sucrose is used as a sweetening agent for foods and in the manufacture of candies, cakes, puddings, preserves, soft and alcoholic beverages, and many other foods. Sugar is used not only as a constituent in home-produced and industrially produced foods, but also as the raw material for fermentation products such as ethyl alcohol, butyl alcohol, glycerin, citric acid, and levulinic acid. Sugar is an ingredient in some transparent soaps, and it can be converted to esters and ethers, some of which yield tough, insoluble, and infusible resins.
GTSB77 sugar beet was developed to allow for the use of glyphosate, the active ingredient in the herbicide Roundup®, as a weed control option. This genetically engineered sugar beet line contains a form of the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that allows it to survive the otherwise lethal application of glyphosate. The EPSPS gene put into GTSB77 was isolated from a strain of the common soil bacterium Agrobacterium tumefaciens called CP4 and the form of EPSPS enzyme produced by this gene is tolerant to glyphosate.
The EPSPS enzyme is part of an important biochemical pathway in plants called the shikimate pathway, which is involved in the production of aromatic amino acids and other aromatic compounds. When conventional plants are treated with glyphosate, the plants cannot produce the aromatic amino acids needed to grow and survive. EPSPS is present in all plants, bacteria, and fungi. It is not present in animals, which do not synthesize their own aromatic amino acids. Because the aromatic amino acid biosynthetic pathway is not present in mammals, birds or aquatic life forms, glyphosate has little if any toxicity for these organisms. The EPSPS enzyme is naturally present in foods derived from plant and microbial sources.
This transgenic sugar beet line was field tested in the United States from 1996 to 1998. GTSB77 was evaluated extensively and no differences were found in the agronomic characteristics, such as plant emergence, seed yield and germination, and disease susceptibility of line GTSB77 compared to non-transformed beet varieties and standard commercial sugar beet varieties. It was demonstrated that the transformed sugar beet line did not negatively affect beneficial or non-target organisms, and it was not expected to impact on threatened or endangered species.
Sugar beet outcrosses, and is largely wind pollinated. It is normally a biennial, developing a large succulent root in the first year and a seed stalk the second. Certain conditions such as low temperatures after planting and longer day length may induce bolting so that a seed stalk is produced during the first growing season. Beet is also highly sensitive to frost and a poor competitor with other plants. During the reproductive phase, large amounts of pollen are produced, which the wind may carry over long distances. The genus Beta is divided into four sections and sugar beet can cross freely with all members of the section Beta to produce fertile progeny. Hybrids between sugar beet and members of the other three sections do not naturally occur without human intervention and hybridization with other members of the Chenopodiaceae family is unlikely. During production of GTSB77, for purposes other than seed production, plants are harvested before the natural onset of the reproductive phase in the same manner that conventional cultivars are grown. Since it is uncommon for sugar beets to bolt, except in fields or plots grown specifically for seed production, there is little opportunity for uncontrolled pollen flow due to adequate isolation distances enforced by seed certification agencies.
The ability of sugar beet to outcross with related plants means that the formation of glyphosate-tolerant hybrids is possible. However, the glyphosate-tolerance trait is not expected to provide a competitive advantage to hybrid plants unless grown in managed environments routinely subjected to glyphosate applications. In the event that a glyphosate-tolerant hybrid survived, the herbicide-tolerant individual could be easily controlled using mechanical and/or other available chemical means. GTSB77 is considered unlikely to increase the weediness potential of any other cultivated plant or native wild species with which it may interbreed.
As used for human consumption, sugar beet is generally converted directly to refined white sugar (which is composed almost entirely of sucrose) through extensive purification processes. The CP4 EPSPS protein introduced into GTSB77 sugar beet was expressed at low levels in the sugar beet tuber, and was not detectable in refined sugar or molasses derived from sugar beet GTSB77. Consequently, there is no anticipated human exposure to this protein as a result of consumption of refined sugar derived from GTSB77 sugar beet.
Sugar beet pulp is a by-product of the refining process and is normally dried and pelleted for use as a livestock feed. In recent years, it has been purified and used as an additive, at levels of less than 1%, in some specific foods, such as food fibre for breakfast cereals. While no direct analysis of these proteins was undertaken in soluble fibre derivatives, it was expected that they would be at negligible concentrations due to the processing steps involved.
Detailed compositional analyses were carried out to establish the nutritional adequacy of glyphosate-tolerant sugar beet GTSB77. The effect of glyphosate use on the composition of sugar beet was also examined. The transgenic GTSB77 line was compared with non-transgenic sugar beets in an analysis of numerous compositional components, including crude ash, crude fibre, crude protein, carbohydrate and dry matter in both tops and roots (both raw and processed). Additional quality components were measured in roots including, invert sugar content, polarization (% sucrose), sodium, potassium and amino nitrogen. No biologically meaningful differences in any compositional or quality parameters relevant to food were identified between non-transgenic, control sugar beet and sugar beet GTSB77. The transgenic GTSB77 sugar beets were tested, both untreated and treated with glyphosate at recommended agronomic application rates. It was concluded that glyphosate-tolerant sugar beet GTSB77 is equivalent to other commercially available sugar beet varieties with respect to composition and nutritional quality.
The presence of naturally occurring toxins and allergens in glyphosate-tolerant sugar beet line GTSB77 was investigated. Saponins are the only known toxicants found in sugar beet and are actively eliminated in sugar processing. It was concluded that saponin levels in sugar beet GTSB77, both treated and untreated with glyphosate, are not a human health risk since: saponins are, in general, at very low levels in sugar beet tissues; sugar beet processing aims to eliminate saponins and other extraneous material from refined sugar products; and saponin levels in both glyphosate-treated and untreated GTSB77 do not differ significantly across seasons and sites, and fall within the range described for traditional sugar beet varieties in the literature.
The potential toxicity and allergenicity of the CP4 EPSPS protein was assessed. No significant homologies between the amino acid sequence of CP4 EPSPS and those of known toxins or allergens were detected. The protein did not display the characteristics usually associated with allergenic substances, and was readily degraded under conditions simulating the mammalian digestive environment. Acute oral gavage studies, in which mice were fed high doses of the CP4 EPSPS protein, did not reveal any toxic effects and provided further support to the conclusion that this protein, and thus the transgenic GTSB77 sugar beet line, possessed little or no potential for toxicity.
Links to Further Information Expand
This record was last modified on Friday, May 5, 2017