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  • Acetohydroxyacid synthase  (2)
  • 1
    ISSN: 1432-2242
    Keywords: Sulfonylurea ; Primisulfuron ; Herbicide ; tolerance ; Acetohydroxyacid synthase ; Detoxification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Inbred lines of corn (Zea mays L.) have been characterized, which exhibit differential sensitivity to the sulfonylurea herbicide primisulfuron (2-[3-(4,6-bis(di-fluoromethoxy) pyrimidin-2-yl)-ureidosulfonyl]-benzoic acid methylester). When treated postemergence with 160 g a.i. per hectare, inbred 4CO exhibited complete tolerance while inbred 4N5 was killed. The F1 hybrid 4C0 x 4N5 was uniformly tolerant indicating dominance of the tolerance trait. The field observations correlated with laboratory tests in which seedling root growth was measured. Based on IC50, inbred 4CO was more than ten times more tolerant than inbred 4N5. In the F2 and F3 generations, a 3∶1 segregation of tolerant and sensitive individuals was observed, consistent with tolerance being inherited as a single dominant trait. Backcrosses of heterozygous F1 plants with the sensitive parent (4N5) yielded progeny that segreated at the expected 1∶1 ratio. Backcrosses with 4C0 yielded tolerant offspring only. Inhibition characteristics of acetohydroxyacid synthase (AHAS; E.C. 4.1.3.18) were determined. The enzymes from both inbreds and their F1 hybrid were equally sensitive and strongly inhibited by primisulfuron (IC50: 7 nM). The fate of 14C-labeled primisulfuron in seedling tissues of inbred 4C0 and the hybrid, 4C0 x 4N5, indicated rapid metabolism with a half-life (t 1/2) of approximately 3 h. On the other hand, the herbicide-sensitive inbred 4N5 was considerably slower to metabolize primisulfuron (t 1/2 〉24 h). These data indicate that differential metabolism is the mechanism of tolerance to the sulfonylurea herbicide primisulfuron in tolerant corn.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Gene amplification ; Mutant gene ; Acetohydroxyacid synthase ; Herbicide resistance ; Nicotiana tabacum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have selected a tobacco cell line, SU-27D5, that is highly resistant to sulfonylurea and imidazolinone herbicides. This line was developed by selection first on a lethal concentration of cinosulfuron and then on increasing concentrations of primisulfuron, both sulfonylurea herbicides. SU-27D5 was tested against five sulfonylureas and one imidazolinone herbicide and was shown, in every case, to be two to three orders of magnitude more resistant than wild-type cells. The acetohydroxyacid synthase (AHAS) of SU-27D5 was 50- to 780-fold less sensitive than that of wild-type cells to herbicide inhibition. The specific activity of AHAS in the SU-27D5 cell lysate was 6 to 7 times greater than that in wild-type cells. Using Southern analysis, we showed that cell line SU-27D5 had amplified its SuRB AHAS gene about 20-fold while maintaining a normal diploid complement of the SuRA AHAS gene. Genomic clones of both AHAS genes were isolated and used to transform wild-type tobacco protoplasts. SuRB clones gave rise to herbicide-resistant transformants, whereas SuRA clones did not. DNA sequencing showed that all SuRB clones contained a point mutation at nucleotide 588 that converted amino acid 196 of AHAS from proline to serine. In contrast, no mutations were found in the SuRA clones. The stability of SuRB gene amplification was variable in the absence of selection. In one experiment, the withdrawal of selection reduced the copy number of the amplified SuRB gene to the normal level within 30 days. In another experiment, amplification remained stable after extended cultivation on herbicide-free medium. This is the first report of amplification of a mutant herbicide target gene that resulted in broad and strong herbicide resistance.
    Type of Medium: Electronic Resource
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