Properties of acetolactate synthase from sulfonylurea-resistant Scirpus juncoides Roxb. var. ohwianus T. Koyama |
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Authors: | Yasushi Tanaka |
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Institution: | Agricultural Research Laboratories, Technical Division, Sumitomo Chemical Takeda Agro Company, Limited, 10 Wadai, Tsukuba, Ibaraki 300-4247, Japan |
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Abstract: | Properties of acetolactate synthase (EC 4.1.3.18; ALS) from sulfonylurea-resistant (SUR) Scirpus juncoides Roxb. var. ohwianus T. Koyama were studied biochemically and physiologically in comparison with those from sulfonylurea-susceptible weed (SUS). GR50 values for growth inhibition and I50 values for ALS inhibition by imazosulfuron were determined for both SUR and SUS. Imazosulfuron controlled the SUS above 80% at the dosage more than 10 g a.i./ha but did not control the SUR at the even great dosage of 1000 g a.i./ha. The rates required for 50% growth inhibition of the SUR relative to the SUS (R/S ratio) were 271-fold. The I50 value for inhibition of ALS from the SUS was 15 nM, compared to I50 of >3000 nM for inhibition of ALS from the SUR. These results suggest that a resistance may due to an altered ALS that is insensitive to imazosulfuron. The Km (pyruvate) value of ALS from the SUR was similar to the Km for ALS from the SUS, suggesting that a mutation resulting in resistance does not change the affinity of the enzyme for pyruvate. The specific activity of the SUR ALS was similar to that of the SUS ALS, which indicates that resistance is not an over-expression of the enzyme. ALS activity from both biotypes was inhibited by isoleucine, valine, and leucine in this order. However, the SUR ALS was less sensitive to inhibition by valine than the SUS ALS. |
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Keywords: | Imazosulfuron Acetolactate synthase Sulfonylurea-resistant weed biotype Scirpus juncoides Roxb var ohwianus T Koyama Feedback inhibition Branched-chain amino acid Valine |
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