, Volume 196, Issue 1, pp 64–68

A double mutant allele, csr1-4, of Arabidopsis thaliana encodes an acetolactate synthase with altered kinetics


DOI: 10.1007/BF00193218

Cite this article as:
Mourad, G., Williams, D. & King, J. Planta (1995) 196: 64. doi:10.1007/BF00193218


A comparison is made of the kinetic characteristics of acetolactate synthase (EC in extracts from Columbia wild type and four near-isogenic, herbicide-resistant mutants of Arobidopsis 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). \(K_{m_{app} } \) 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. The data suggest that (i) single mutational changes occurred that affected the binding of herbicides to the acetolactate synthase molecule without influencing the binding of substrates and feedback inhibitors (e.g. csr1-1, csr1-2 and csr1-3) and (ii) bringing two of these single mutations (csr1-1 and csr1-2) together in a double mutant (csr1-4) gave rise to an enzyme with altered characteristics as well as plants with changed growth in response to added L-Val and L-Leu. The implications of these conclusions for genetic transformation using these herbicide-resistant genes are discussed.

Key words

Acetolactate synthaseArabidopsisEnzyme kineticsHerbicide resistanceMutant



acetolactate synthase







Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  1. 1.Department of BiologyIndiana-Purdue UniversityFort WayneUSA
  2. 2.Department of BiologyUniversity of SaskatchewanSaskatoonCanada