Database Product Description
- Host Organism
- Oryza sativa (Rice)
- Imidazolinone herbicide tolerance, specifically imazethapyr.
- Trait Introduction
- Chemically induced seed mutagenesis
- Proposed Use
Production for human food, livestock feed and industrial uses.
- Product Developer
- BASF Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Oryza sativa (Rice) Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
This product was not subject to regulation in any jurisdiction except Canada since the development of this herbicide-tolerant line did not employ recombinant DNA technologies. In Canada, regulatory approval was required for use in human food and livestock feed, but not for environmental release as these lines were not intended for cultivation in Canada.
Harvested rice, also known as rough rice or paddy rice, is encased by an inedible hull, which is removed prior to milling. Rice hulls are used as fuel, mulch, abrasives, and in animal feed products. Brown rice is what remains after the hulls are removed. The light brown colour of brown rice is due to the presence of bran layers and the rice germ surrounding the rice kernel. Brown rice is further milled to remove the bran and germ to yield white rice, or ‘polished rice.’ The bran and germ are high in protein and other nutrients, and are used in specialty foods, such as rice bran oil, and in livestock feed. Rough rice may be parboiled prior to milling: this involves soaking, steaming and drying the rice. Parboiling improves milling yield and also preserves some of the B vitamin content of the milled rice. Both brown and white rice kernels can be processed into rice flour for use in breakfast cereals, baby foods, desserts and other food products. Rice kernels are also used to produce beer and wine.
Weeds are a significant production problem in rice cultivation. Weeds of rice producing areas, such as the United States, include red rice (Oryza spp.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.). These are typically managed using a combination of cultural practices (e.g., dry vs wet tillage, using clean seed, crop rotations) and chemical controls (herbicides such as molinate and propanil).
The rice line PWC16 was developed to allow the use of imazethapyr, an imidazolinone herbicide, as a weed control option in rice production. The mode of action of imazethapyr consists of inhibiting the activity of acetohydroxyacid synthase (AHAS), an enzyme in plants active in glycolysis and in the biosynthesis of the branched-chain amino acids isoleucine, leucine and valine. The result of the inhibition of AHAS activity is a decrease in protein synthesis, and in an accumulation of toxic levels of alpha-ketoglutarate, all of which causes the eventual death of the plant. While unmodified rice is not tolerant to imazethapyr, the line PWC16 has been modified to survive an otherwise lethal application of this herbicide. PWC16 was developed using chemically induced seed mutagenesis and whole plant selection procedures. The herbicide tolerance is due to a mutation in the AHAS gene, which codes for an alteration in the binding site for imazethalpyr in the AHAS enzyme.
Cultivated rice is primarily self-pollinating; however, it may cross-pollinate with other cultivated rice varieties, although the rates are less than one percent. Factors limiting cross-pollination include flower morphology (short style and stigma, short anthers), inability of the pollen to remain viable longer than a few minutes, and a lack of insect vectors for pollen spread. In the United States, the only wild species known to be compatible with cultivated rice are O. rufipogon, which has been found in a single location in the Everglades of Florida, and red rice (O. sativa ssp.). Due to the relative isolation of O. rufipogon, it is unlikely to hybridize with cultivated rice. Cross-pollination may, however, occur with red rice under suitable conditions, form imazethapyr-tolerant hybrids. Although PWC16 is not intended for cultivation in Canada, any unintentional release would not be of concern since there are no species that are sexually compatible with rice, and due to environmental conditions, the plants would not persist.
Data submitted on the vegetative vigour, time to maturity and seed production of PWC16 were found to be within the normal range of expression of these traits displayed by unmodified rice varieties. It was determined that the tolerance to imazethapyr in PWC16 will not render it weedy, invasive of natural habitats, or allow it to grow outside of its adapted environment, since none of the reproductive or growth characteristics were modified.
The food and livestock safety of PWC16 rice was established based on: the evaluation of the similarity of AHAS, in structure and function, to the enzyme naturally present in food and livestock feeds; the fact that the modified AHAS constitutes a small amount of the protein in PWC16 rice, so there is little dietary exposure; the lack of toxicity or allergenicity of AHAS from plants; and, studies on the function of this enzyme in PWC16 compared to its unmodified counterpart. The nutritional equivalence and wholesomeness of PWC16 was demonstrated by the analysis of key nutrients, including proximates (protein, crude fat, crude fibre, ash and carbohydrates), amino acid and fatty acid composition, vitamins, as well as anti-nutrients.
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This record was last modified on Friday, March 26, 2010