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Altered acetolactate synthase activity in ALS-inhibitor resistant prickly lettuce (Lactuca serriola)

Published online by Cambridge University Press:  12 June 2017

Mary J. Guttieri
Affiliation:
University of Idaho, Aberdeen, ID 83210
Carol A. Mallory-Smith
Affiliation:
Oregon State University, Corvallis, OR 97331
Donn C. Thill
Affiliation:
University of Idaho, Moscow, ID 83843
Roger J. Baerg
Affiliation:
American Cyanamid, Princeton, NJ 08543

Abstract

The effect of target site mutation for acetolactate synthase (ALS)-inhibitor resistance on ALS activity was evaluated in a sulfonylurea-resistant (R) biotype of prickly lettuce with a proline173 to histidine substitution in Domain A of the ALS enzyme. I50 values for ALS inhibition by several ALS-inhibitor herbicides were determined for R and susceptible (S) biotypes. Results from both a standard ALS assay and a chloroplast assay for ALS activity showed that the R biotype also was cross-resistant to representatives of the imidazolinone (imazethapyr) and triazolopyrimidine (flumetsulam) families, but was not cross-resistant to the pyrimidinyl oxybenzoate (4,6-dimethoxypyrimidin-2-y 1-oxy-2-benzoic acid) tested. The K m (pyruvate) was similar for ALS extracted from the R and S biotypes, suggesting that mutation for resistance did not alter pyruvate binding on the enzyme. However, specific activity of ALS from the R biotype was 57% less than specific activity of ALS from the S biotype, suggesting that the resistance mutation may affect enzyme function, expression, or stability. ALS from the R biotype was less sensitive to inhibition by the branched chain amino acids, valine, leucine, and isoleucine, than ALS from the S biotype. Reduced sensitivity to feedback inhibition was correlated with 70, 40, and 9% higher concentrations of valine, leucine, and isoleucine, respectively, on a per seed basis in R vs. S seed.

Information

Type
Physiology, Chemistry, and Biochemistry
Copyright
Copyright © 1997 by the Weed Science Society of America 

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