Effect of four classes of herbicides on growth and acetolactate-synthase activity in several variants of Arabidopsis thaliana

Abstract

We have isolated a triazolopyrimidine-resistant mutant csrl-2, of Arabidopsis thaliana (L.) Heynh. Here, we compare csrl-2 with the previously isolated mutants csrl and csr1-1, and with wild-type Arabidopsis for responses to members of four classes of herbicides, namely, sulfonylureas, triazolopyrimidines, imidazolinones, and pyrimidyl-oxy-benzoates. Two separable herbicide binding sites have been identified previously on the protein of acetolactate synthase (ALS). Here, the mutation giving rise to csrl, originating in a coding sequence towards the 5' end of the ALS gene, and that in csrl-2, affected the inhibitory action on growth and ALS activity of sulfonylurea and triazolopyrimidine herbicides but not that of the imidazolinones or pyrimidyl-oxybenzoates. The other mutation, in csrl-1, originating in a coding sequence towards the 3' end of the ALS gene, affected the inhibitory action of imidazolinones and pyrimidyl-oxy-benzoates but not that of the sulfonylureas or triazolopyrimidines. Additional, stimulatory effects of some of these herbicides on growth of seedlings was unrelated to their effect on their primary target, ALS. The conclusion from these observations is that one of the two previously identified herbicide-binding sites may bind sulfonylureas and triazolopyrimidines while the other may bind imidazolinones and pyrimidyl-oxy-benzoates within a herbicide-binding domain on the ALS enzyme. Such a comparative study using near-isogenic mutants from the same species allows not only the further definition of the domain of herbicide binding on ALS but also could aid investigation of the relationship between herbicide-, substrate-, and allosteric-binding sites on this enzyme.This research was supported by an Operating Grant from the Natural Sciences and Engineering Research Council of Canada to J.K.

Characterization of Acetohydroxyacid Synthase I fromEscherichia coliK-12 and Identification of Its Inhibitors

“…[5][6][7][8] In this study, we examined the inhibition of E. coli K-12 AHAS I using several herbicides, including the sulfonylurea derivatives chlorimuron ethyl (CE), chlorsulfuron (CS), metsulfuron methyl (MSM), sulfometuron methyl (SMM), pirimisulfuron (PSM), nicosulfuron (NS), bensulfuron methyl (BSM), and pyrazosulfuron ethyl (PSE), along with thifensulfuron methyl (TSM) and the imidazolinone derivatives imazapyr, imazethapyr, imazapic, and imazaquin. The structures of these herbicides have been published.…”

“…3,4) AHAS is the site of action of sulfonylurea, imidazolinone, triazolopyrimidine, and pyrimidylbenzoate herbicides, [5][6][7][8] which might operate by binding to the regulatory site on the enzyme. 7) AHAS activity is found in bacteria, fungi, and plants, and is contributed by one or more isozymes.…”

Expression, purification and characterization of Arabidopsis thaliana acetohydroxyacid synthase

“…AHAS is the site of action of four different classes of herbicide ; sulphonylureas, imidazolinones, triazolopyrimidines and pyrimidyl(oxy)benzoates [5][6][7][8]. These herbicides may bind to the regulatory site on the enzyme [7].…”

Mutagenesis studies on the sensitivity of Escherichia coli acetohydroxyacid synthase II to herbicides and valine

“…In plant and yeast AHAS there is a proline residue at the equivalent sequence position, and mutation to serine results in herbicide resistance [6][7][8][9][10][11]. Moreover, Mazur and Falco [5] reported that the S100P (Ser"!!…”

“…An imidazolinone-resistant mutant of A. thaliana AHAS has been isolated [10,12,13] and shown to contain a mutation of S653 to asparagine. The apparent K i for imazethapyr of this mutant is 1.9 mM [4], very similar to that of wild-type E. coli AHAS II (0.78 mM).…”