We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to .
To save content items to your Kindle, first ensure coreplatform@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
Biochemical and physiological effects of target site resistance to herbicides inhibiting acetolactate synthase (ALS) were evaluated using sulfonylurea-resistant (R) and -susceptible (S) near isonuclear Lactuca sativa ‘Bibb’ lines derived by backcrossing the resistance allele from Lactuca serriola L. into L. sativa. Sequence data suggest that resistance in L. sativa is conferred by a single-point mutation that encodes a proline197 to histidine substitution in Domain A of the ALS protein; this is the same substitution observed in R L. serriola. Kmapp (pyruvate) values for ALS isolated from R and S L. sativa were 7.3 and 11.1 mM, respectively, suggesting that the resistance allele did not alter the pyruvate binding domain on the ALS enzyme. Both R and S ALS had greater affinity for 2-oxobutyrate than for pyruvate at the second substrate site. Ratios of acetohydroxybutyrate: acetolactate produced by R ALS across a range of 2-oxobutyrate concentrations were similar to acetohydroxybutyrate: acetolactate ratios produced by S ALS. Specific activity of ALS from R L. sativa was 46% of the specific activity from S L. sativa, suggesting that the resistance allele has detrimental effects on enzyme function, expression, or stability. ALS activity from R plants was less sensitive to feedback inhibition by valine, leucine, and isoleucine than ALS from S plants. Valine, leucine, and isoleucine concentrations were about 1.5 times higher in R seed than in S seed on a per gram of seed basis, and concentrations of valine and leucine were 1.3 and 1.6 times higher, respectively, in R leaves than in S leaves. Findings suggest that the mutation for resistance results in altered regulation of branched-chain amino acid synthesis.
Email your librarian or administrator to recommend adding this to your organisation's collection.