A method for controlling the growth of undesired vegetation growing at a locus where a plant has been cultivated, said plant having been transformed with an isolated nucleic acid fragment comprising a nucleotide sequence encoding a plant acetolactate synthase protein which is resistant to a compound selected from the group consisting of sulfonylurea, triazolopyrimidine sulfonamide, and imidazolinone herbicides, said nucleotide sequence comprises at least one sub-sequence which encodes one of the substantially conserved amino acid sub-sequences designated A, B, C, D, E, F, and G, in FIG. 6, the nucleic acid fragment is further characterized in that at least one of the following conditions is met,
- (a) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence A wherein .epsilon..sub.1 is an amino acid other than alanine, or .epsilon..sub.2 is an amino acid other than glycine,
- (b) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence B wherein .alpha..sub.1 is an amino acid other than proline,
- (c) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence C wherein .delta..sub.2 is an amino acid other than alanine,
- (d) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence D wherein .lambda..sub.1 is an amino acid other than lysine,
- (e) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence E wherein .gamma..sub.1 is an amino acid other than aspartic acid,
- (f) the nucleic acid fragment has a sequence which encodes an amino acid sub-sequence F wherein .beta..sub.3 is an amino acid other than tryptophan, or .beta..sub.8 is an amino acid other than valine or .beta..sub.7 is an amino acid other than phenylalanine, and
- (g) the nucleic acid has a sequence which encodes an amino acid sub-sequence G wherein .sigma..sub.1 is an amino acid other than methionine,
- said method comprising applying to the locus an effective amount of said herbicide.