GM Crop Database

Database Product Description
Host Organism
Zea mays L. L. (Maize)
Imidazolinone herbicide tolerance.
Trait Introduction
Selection of somaclonal variants from embryo cultures.
Proposed Use
Production of Z. mays for human consumption (wet mill or dry mill or seed oil), and meal and silage for livestock feed. These materials will not be grown outside the normal production area for corn.
Company Information
Pioneer Hi-Bred International Inc.
7100 NW 62nd Avenue
PO Box 1150
Summary of Regulatory Approvals
Country Environment Food and/or Feed Food Feed Marketing
Canada 1996 1994 1996  
Click on the country name for country-specific contact and regulatory information.
General Description
1. Imidazolinone Tolerance

Imidazolinones comprise a class of herbicide which target and bind to the acetolactate synthase (ALS) enzyme thereby inhibiting the biosynthesis of branched chain amino acids, resulting in a decrease in protein synthesis and eventual death of the plant. ALS catalyses the first reaction in the biosynthesis of the essential branched chain amino acids valine, leucine and isoleucine and is active in the glycolytic pathway of plant metabolism.

Imidazolinone tolerance in 3751IR corn results from a mutation in the ALS enzyme. The mutant form of ALS in 3751IR prevents the binding of imidazolinone herbicides to the enzyme. Imidazolinones applied at rates recommended for effective weed control are phytotoxic to currently cultivated corn varieties.

The levels of valine, leucine and isoleucine are also regulated by feedback inhibition. Pioneer has provided literature references to show that the mutant ALS of the inbred line XA17, from which the hybrid 3751IR is derived, does not affect feedback inhibition and hence, the regulation of levels of these amino acids.

The levels of valine, leucine and isoleucine in whole plant extracts of 3751IR and its counterpart 3751, were not statistically different, showing that the activity of the ALS enzyme in 3751IR has not been affected by the mutation.
2. Development Method

Somatic embryos grown on imidazolinone enriched media were selected, and from these, the somaclonal variant cell line XA17 was isolated. This cell line was regenerated to a whole plant and crossed to the inbred line B73.

The XA17/B73 line was backcrossed into each of two proprietary Pioneer inbreds which were then crossed to produce the hybrid 3751IR.
3. Stability of Trait

The imidazolinone tolerance trait was shown to be stable and to display regular Mendelian segregation in progeny from XA17 crosses with several corn inbreds.

3751IR is homozygous for the imidazolinone tolerance trait. Homozygous progeny were found to be tolerant to imidazolinone at up to four times the recommended rate for soybeans. Heterozygous progeny, while expressing the herbicide tolerance trait, exhibited pronounced leaf chlorosis and stunted growth at these herbicide rates.
Reference: Canadian Food Inspection Agency, Plant Biotechnology Office

Summary of Introduced Genetic Elements
Code Name Type Promoter, other Terminator Copies Form
als acetolactate synthase  (Z. mays) MUT NULL
NULL   Imidazolinone selection of somatic embryos

Characteristics of Zea mays L. (Maize)
Center of Origin Reproduction Toxins Allergenicity
Mesoamerican region, now Mexico and Central America Cross-pollination via wind-borne pollen is limited, pollen viability is about 30 minutes. Hybridization reported with teosinte species and rarely with members of the genus Tripsacum. No endogenous toxins or significant levels of antinutritional factors. Although some reported cases of maize allergy, protein(s) responsible have not been identified.

Links to Further Information
Canadian Food Inspection Agency, Plant Biotechnology Office[PDF Size: 145926 bytes]
Decision Document DD96-10: Determination of Environmental Safety of 3751IR, an Imidazolinone-tolerant Corn (Zea mays L.) Hybrid developed by Pioneer Hi-Bred International Inc.
Office of Food Biotechnology, Health Canada[PDF Size: 46422 bytes]

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