GM Crop Database

Database Product Description

GTSB77 (SY-GTSB77-7)
Host Organism
Beta vulgaris (Sugar Beet)
Trade Name
InVigor™
Trait
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

Country Food Feed Environment Notes
Australia 2002
Japan 2003 2003
New Zealand 2002
Philippines 2004 2004
United States 1998 1998 1998

Introduction Expand

Sugar beet line GTSB77 was developed using recombinant DNA techniques to allow the use of glyphosate, the active ingredient in the herbicide Roundup®, as a weed control option in sugar beet crops. The novel plants express an herbicide tolerant form of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) derived from the common soil bacterium, Agrobacterium tumefaciens strain CP4. Glyphosate specifically binds to and inactivates EPSPS, which is involved in the synthesis of the aromatic amino acids, tyrosine, phenylalanine and tryptophan (shikimate biochemical pathway). EPSPS is present in all plants, bacteria, and fungi but not in animals, which must obtain these essential amino acids from their diet. Because the aromatic amino acid biosynthetic pathway is not present in mammalian, avian or aquatic life forms, glyphosate has little if any toxicity for these organisms. The EPSPS enzyme is normally present in food derived from plant and microbial sources.

The plasmid used during the transformation of this sugar beet line also contained a second gene that encoded the enzyme glyphosate oxidase (GOX) from the bacterium Ochrobactrum anthropi. This enzyme was intended to accelerate the normal degradation of glyphosate into aminomethylphosphonic acid (AMPA) and glyoxylate in plant cells. Upon insertion into the plant genome, the GOX encoding gene was truncated and fused to genomic sugar beet DNA sequences, resulting in a chimeric sequence that did not express a functional protein.

Line GTSB77 expresses a reporter gene (uidA) encoding the enzyme beta-D-glucuronidase (GUS) from E. coli. The expression of GUS activity was used during the development phase to identify transgenic plants containing the introduced gene sequences.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
CP4 epsps 5-enolpyruvyl shikimate-3-phosphate synthase HT

figwort mosaic virus (FMV) 35S

chloroplast transit peptide from A. thaliana

Pisum sativum (pea) ribulose-1,5-bisphosphate carboxylase small subunit non-translated region

Native

gus beta-D-glucuronidase SM CaMV 35S pea ribulose-1,5-bisphosphate carboxylase small subunit Native
goxv247 glyphosate oxidoreductase HT figwort mosaic virus (FMV) 35S chloroplast transit peptide from A. thaliana Truncated

Characteristics of Beta vulgaris (Sugar Beet) Expand

Center of Origin Reproduction Toxins Allergenicity

Beta is considered an Old World genus basically confined to the Mediterranean Basin and Middle East.

Sugar beet is an outcrossing, largely wind pollinated, plant. During the reproductive phase, large amounts of pollen are produced which can travel long distances. Sugar beet hybridizes freely with all members of the section Beta (within genus Beta).

Saponins (triterpenoid glycosides) are the only known toxicants found in sugar beet and are actively eliminated in sugar processing.

There are rare reports of allergic reactions in sugar beet field workers, associated with exposure to the seeds of the plant.

Donor Organism Characteristics Expand

Latin Name Gene Pathogenicity
Agrobacterium tumefaciens strain CP4 CP4 epsps

Agrobacterium tumefaciens is a common soil bacterium that is responsible for causing crown gall disease in susceptible plants. There have been no reports of adverse effects on humans or animals.

Modification Method Expand

Sugar beet line GTSB77 was produced by Agrobacterium-mediated transformation of the proprietary cytoplasmic male sterile sugar beet line A1012 with plasmid PV-BVGT03. The T-DNA region of the Agrobacterium Ti plasmid used to develop line GTSB77 contained sequences encoding CP4 EPSPS, glyphosate oxidase (GOX), neomycin phosphotransferase II (NPTII), and GUS.

Associated with the CP4 EPSPS encoding gene were promoter sequences derived from the 35S transcript of figwort mosaic virus (FMV), sequences encoding the chloroplast transit peptide (CTP2) from the Arabidopsis thaliana EPSPS gene, and transcription termination and polyadenylation signal sequences from the ribulose-1,5-bisphosphate carboxylase small subunit (rbcS; rubisco) encoding gene from pea (Pisum sativum).

Expression of the GUS encoding uidA gene was regulated using the enhanced 35S promoter from cauliflower mosaic virus (CaMV) and the transcription termination sequences from the 3’ region of the pea rbcS encoding gene. The regulatory sequences linked to the Ochrobactrum anthropi GOX encoding gene included the FMV 35S promoter, CTP1 signal sequence from the small subunit 1A of rubisco from A. thaliana, and 3’ termination sequences from the A. tumefaciens nopaline synthase gene.

Characteristics of the Modification Expand

The Introduced DNA

Southern blot analyses of genomic DNA from GTSB77 confirmed the existence of a single copy of the T-DNA region containing complete functional copies of the CP4 EPSPS and GUS encoding genes, and a partial non-functional copy of the GOX encoding gene. This partial copy of the GOX encoding sequences was due to a 3’ truncation of the T-DNA insert, which also resulted in no integration of NPTII encoding sequences into the host genome.

The truncated copy of the goxv247 gene was fused with genomic sugar beet DNA sequences, forming a chimeric sequence consisting of 69% of the entire GOX coding sequence plus 130 bp of host sequence terminated with an identified translational stop codon. While mRNA transcripts from this chimeric sequence were identified in GTSB77, a protein fusion product was never detected, and plant tissue extracts contained no detectable GOX enzyme activity.

Genetic Stability of the Introduced Trait

Phenotypic segregation analysis of the glyphosate-tolerant trait and GUS activity were conducted over multiple generations and confirmed an inheritance pattern consistent with the stable transfer of a single dominant locus for these genes. These phenotypes were also shown to be stable over multiple generations in successive cropping.

Expressed Material

Sugar beet line GTSB77 expressed two novel proteins CP4 EPSPS and GUS. The CP4-EPSPS protein is 47.6 kDa in size and consists of a single polypeptide of 455 amino acids. The GUS protein was experimentally determined to have a molecular weight of 68.2kD.

These proteins were detected in very low levels in root tissue of sugar beet GTSB77 (58 ppm and 0.5 ppm for CP4 EPSPS and GUS respectively). They were also present at higher levels in leaf and stem tissue (237 ppm and 3 ppm for CP4-EPSPS and GUS respectively).

As previously mentioned, the chimeric sequence formed between the truncated goxv247 gene and 130 bp of plant genome sequence gave rise to the possibility that a novel protein could be expressed. The expression of such a GOX-like protein was investigated by Western immunoblot analysis using antibodies raised to a 46 kDa protein (designated 34550) expressed in E. coli containing a cloned copy of the chimeric sequence. This protein was comprised of 89 amino acids from the CTP1 transit peptide, the N-terminal 299 amino acids from GOX, and 43 amino acids encoded by sugar beet genomic DNA. Western blot analysis, on plant tissue extracts from several locations, determined that protein 34550 was not present at a detection limit of 180 ppb in plant tissue.

An ancillary study was undertaken to determine the presence of GOX activity by monitoring the production of glyoxylate, the breakdown product of glyphosate. No detectable GOX-like activity could be demonstrated for protein 34550 purified from E. coli. A similar study confirmed that sugar beet GTSB77 did not display GOX activity.

Environmental Safety Considerations Expand

Field Testing

The transgenic sugar beet line GTSB77 was field tested in the United States (1996 – 1998). GTSB77 was evaluated extensively and agronomic data showed that there were no significant changes in the number of seeds produced, germination characteristics, final stand, over-wintering capability, or pathogen susceptibility.

Outcrossing

Sugar beet is an outcrossing, largely wind pollinated, plant. 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 and produce a seed stalk 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 can travel long distances. The genus Beta, including the wild relatives, is divided into four sections: Beta, Corolinnae, Procumbentes, and Nanae. Sugar beet hybridizes freely with all members of the section Beta and the resulting progeny are fertile but hybridization is unlikely with other members of the Chenopodiaceae family. Hybrids between sugar beet and members of the other three sections do not naturally occur without human intervention. Assuming proximity, synchrony of flowering and suitable conditions, B. vulgaris may freely hybridize with other varieties.

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 unmodified 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.

Specific concerns have been raised about potential outcrossing with subsp. macrocarpa, in the Imperial Valley, California. Isozyme studies indicated the introgression of genes from commercial sugar beets has occurred, although other reports show that gene flow between these two plant populations is not likely due to non-synchronous flowering periods, sterile F1 hybrids, and poor growth in F2 hybrids.

It was determined that the transgenic sugar beet line GTSB77 was no more likely to become a weed than herbicide tolerant cultivars currently in use or that can be developed by traditional breeding techniques. GTSB77 was unlikely to increase the weediness potential of any other cultivated plant or native wild species with which it may interbreed.

Weediness

Sugar beet plants are not a serious weed, although sugar beets have escaped cultivation and their progeny have persisted in the environment for many years. Occasionally, sugar beet volunteers may arise from the presence of wild beet, the bolting of fodder beet plants, the development of groundkeepers which arise initially from vegetative growth of beet crowns or tops left after harvest or the germination of seed (which may be dormant in the soil for up to 10 years). Volunteer plants may be controlled by mechanical means or the use of registered herbicides that can be used on sugar beet volunteers.

Sugar beet plants have escaped from past commercial cultivation in the San Francisco Bay area and persist to this day. However, transgene movement via pollen to these plants is highly unlikely as sugar beets are no longer in commercial production in the Bay area. Other populations of sexually compatible plants are located in the Imperial Valley of California, but no wild populations exist outside of California.

The movement of the glyphosate tolerance trait from GTSB77 to any other sexually compatible plant should not have a significant impact as the glyphosate tolerance would not confer any competitive advantage to these plants, especially if glyphosate is not applied to these plants. This would only occur in managed ecosystems where glyphosate is applied for broad-spectrum weed control, or in plant varieties developed to exhibit glyphosate tolerance and in which glyphosate is used to control weeds. As with glyphosate tolerant sugar beet volunteers, these individuals, should they arise, would be controlled using other available chemical means. Hybrids, if they developed, could potentially result in the loss of glyphosate as a tool to control these species. However, this can be avoided by the use of sound crop management practices including not using the same herbicide every year.

Secondary and Non-Target Adverse Effects

It was concluded that the genes inserted into the transgenic sugar beet line GTSB77 would not result in any deleterious effects or significant impacts on nontarget organisms, including threatened and endangered species or beneficial organisms. The enzyme EPSPS that confers glyphosate resistance is from a commonly occurring soil bacterium, A. tumefaciens, and is similar to the gene that is normally present in sugar beets and is not known to have any toxic properties. Field observations of line GTSB77 revealed no negative effects on nontarget organisms. The lack of known toxicity for this enzyme suggests no potential for deleterious effects on beneficial organisms such as bees and earthworms. The high specificity of the enzyme for its substrates makes it unlikely that the introduced enzyme would metabolize endogenous substrates to produce compounds toxic to beneficial organisms.

The chimeric-GOX fusion protein (Protein 34550) was unlikely to pose any risk. First, the amount was not detectable in plant tissue, it had no enzymatic activity, and the protein it was fused to is a normal constituent of sugar beets. Additionally, the scoreable marker protein, beta-D-glucuronidase, is a well-characterized protein with no known toxicity.

Impact on Biodiversity

Genetically engineered line GTSB77 sugar beet is no more likely to become a weed than herbicide tolerant cultivars currently in use or that can be developed by traditional breeding techniques. It is unlikely to increase the weediness potential of any other cultivated plant or native wild species with which it may interbreed. It will not harm non-target organisms and there is no potential impact of line GTSB77 on biodiversity.

Food and/or Feed Safety Considerations Expand

Dietary Exposure

Sugar beet is generally converted directly to refined white sugar (which is composed almost entirely of sucrose) through extensive purification processes. Analysis of highly refined sugar liquor and crystalline sugar from sugar beet showed that total protein within derivative food products ranged from 0.004 to 1.2 µg per g. CP4-EPSPS and GUS proteins were expressed at low levels in the sugar beet root, and none of these proteins, including Protein 34550 were detected in refined sugar or molasses derived from sugar beet GTSB77.

Sugar beet pulp is a by-product that, in recent years, has been purified and used as an additive, at less than 1%, in some specific foods such as food fibre for breakfast cereals etc. 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.

It was concluded that little if any CP4-EPSPS or GUS protein would be consumed as a consequence of eating food containing sugar derived from sugar beet GTSB77. Thus exposure to the novel proteins was likely to be extremely low.

Nutritional Data

Detailed compositional analyses conducted over multiple years and geographic regions (United States and Europe) 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. Analyses included crude ash, crude fibre, crude protein, carbohydrate and dry matter in both tops and roots (both raw and processed into brei powder used in sugar production). Additional quality components were measured in roots including, invert sugar (glucose + fructose) content, polarization (% sucrose), sodium, potassium and amino nitrogen. No biologically meaningful differences in any compositional and quality parameters relevant to food were identified between non-transgenic, control sugar beet and sugar beet GTSB77, both untreated or treated with glyphosate at recommended agronomic application rates. It is concluded that glyphosate-tolerant sugar beet is equivalent to other commercially available sugar beet with respect to composition and nutritional quality. No nutritional risks are posed by consuming food derived from glyphosate-tolerant sugar beet GTSB77.

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 considered to pose a risk to human health 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.

Toxicity data

The low potential toxicity and allergenicity of the CP4 EPSPS and GUS proteins were assessed. While no evidence of the presence of Protein 34550 was found in sugar beet GTSB77, toxicity studies of the protein were still carried out.
There was no evidence to indicate that the CP4-EPSPS, GUS or Protein 34550 had the potential to be either toxic or allergenic to humans. Proteins from the EPSPS or GUS family of proteins are naturally present in our food supply or expressed in human intestinal microflora. The GOX like protein (Protein 34550) was not normally present in foods, but does not possess any of the characteristics common to many allergens or toxins or any significant sequence similarity to any known allergens or toxins. Furthermore, none of the proteins were detectable in the principal food components sugar and molasses, and in sugar beet pulp; CP4-EPSPS and GUS were negligible, detected at levels of 50 ppm and 1 ppm respectively. The levels of CP4-EPSPS and GUS proteins in sugar beet GTSB77 are extremely low in the root (0.005% and 0.00006% respectively) and Protein 34550 was undetectable at a limit of detection of 100 ppb.
In order to assess the safety of these proteins, sufficient amounts of each respective protein were obtained by cloning the genes, CP4-EPSPS, gus and chimeric-gox, into E. coli. CP4-EPSPS and GUS proteins derived from E. coli were shown to be equivalent for safety assessment purposes. As no Protein 34550 was identified in sugar beet GTSB77 tissue, no equivalence of the E. coli cloned Protein 34550 could be established. PCR analysis using primers specific to the truncated goxv247 gene did, however, showed that the sizes of the genes in both sugar beet GTSB77 and E. coli were equivalent at approximately 1273 bp.

To directly assess the potential toxicity of the CP4-EPSPS, GUS and 34550 proteins acute gavage tests were undertaken in mice using purified forms of each protein. Despite the experimental level of all three proteins being well in excess of the likely human dietary exposure factor, no mortality or morbidity resulted and there were no significant differences in terminal body weights between the treated and control groups. Upon necropsy, body cavities were opened and organs examined in situ and removed. No pathological findings attributable to the treatment with any protein were observed. All three proteins had no toxic effects on mice given acute doses of the equivalent bacterially produced proteins.

It was concluded that the food products derived from sugar beet GTSB77 should pose no greater risk as a source of toxins or allergens than food products derived from conventional sugar beets.

Allergenicity

The potential for the novel proteins to be allergenic was investigated using a number of criteria, including amino acid sequence homology with known allergens, history of use and common physicochemical properties of allergens, including the sensitivity to digestion by digestive enzymes.

Amino acid sequence similarity with known allergens was used as an indicator of the allergenic potential of novel proteins. The amino acid sequence of the CP4-EPSPS, GUS and 34550 proteins were compared to the amino acid sequences of 219 known allergens present in public domain databases (e.g., GenBank, EMBL, Swissprot, PIR). Sequence similarity was defined as a sequence identity of greater than seven contiguous amino acids. No biologically significant similarity was found between any of the novel proteins with any of allergens listed in these databases.
Allergenic proteins in known allergenic foods (such as milk, soybeans and peanuts) exist as major proteins. There was very limited potential for the novel proteins from sugar beet GTSB77 to act as allergens in final food products as: none of the novel proteins could be detected in either sugar or molasses derived from sugar beet GTSB77, and dietary fibre refined from pulp derived from sugar beet GTSB77 would contain extremely low levels of CP4-EPSPS and GUS. Protein 34550 was not detected in pulp samples.

The CP4-EPSPS, GUS and 34550 proteins were degraded rapidly after exposure to simulated gastric fluid. Such rapid digestion would severely limit the amount of protein absorbed via the intestine and thus restrict any potential immunological response. The rate of degradation of these novel proteins was assessed in simulated gastric (SGF) and intestinal fluids (SIF). The degradation of C4 EPSPS, GUS and Protein 34550 were followed, either through Western blot or enzyme activity assays, in both SGF and SIF at 37C. CP4-EPSPS protein was shown to have a half-life of 15 sec in SGF and 10 min in SIF. No detectable GUS protein was present after 15 sec exposure to SGF and over 50% had been degraded in SIF after 60 to 120min. Over 90% of GUS activity had dissipated after 4 hr in SIF. Protein 34550 was degraded within 15 seconds exposure to SGF and within 60 seconds exposure to SIF, moreover no intermediate stable protein fragments larger that 2kD were generated by digestion of Protein 34550 in either SGF or SIF. On the basis of these data all three novel proteins were demonstrated to be readily digestible.

In summary, none of the novel proteins expressed in GTSB77 possess characteristics normally associated with protein allergens, and their potential for eliciting an allergenic response was judge to be extremely remote.

Abstract Collapse

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