A double mutant allele, csr1-4, of Arabidopsis thaliana encodes an acetolactate synthase with altered kinetics.
A comparison is made of the kinetic characteristics of acetolactate synthase (EC 4.1.3.18) in extracts from Columbia wild type and four near-isogenic, herbicide-resistant mutants of Arabidopsis thaliana (L.) Heynh. The mutants used were the chlorsulfuron-resistant GH50 (csr1-1), the imazapyr-resistant GH90 (csr1-2), the triazolopyrimidine-resistant Tzp5 (csr1-3) and the multiherbicide-resistant, double mutant GM4.8 (csr1-4), derived from csr1-1 and csr1-2 by intragenic recombination (G. Mourad et al. 1994, Mol. Gen. Genet. 243, 178-184). Kmapp and Vmax values for the substrate pyruvate were unaffected by any of the mutations giving rise to herbicide resistance. Feedback inhibition by L-valine (L-Val), L-leucine (L-Leu) and L-isoleucine (L-Ile) of acetolactate synthase extracted from wild type and mutants fitted a mixed competitive pattern most closely. Ki values for L-Val, L-Leu and L-Ile inhibition were not significantly different from wild type in extracts from csr1-1, csr1-2, and csr1-3. Ki values were significantly higher than wild type by two- and five-fold, respectively, for csr1-4 with L-Val and L-Leu but not L-Ile. GM4.8 (csr1-4) plants were also highly resistant in their growth to added L-Val and L-Leu.(ABSTRACT TRUNCATED AT 250 WORDS)
Mourad
G
G
Department of Biology, Indiana-Purdue University, Fort Wayne 46805-1499, USA.
Williams
D
D
King
J
J
D000095:Acetolactate Synthase / Q000235:genetics / Q000378:metabolism*; D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D007532:Isoleucine / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology; D009154:Mutation; D011773:Pyruvates / Q000493:pharmacokinetics; D019289:Pyruvic Acid; D014633:Valine / Q000494:pharmacology
D011773:Pyruvates; D007532:Isoleucine; D019289:Pyruvic Acid; D000095:Acetolactate Synthase; D007930:Leucine; D014633:Valine