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PRICKLY LETTUCE (Lactuca serriola)
with GROUP B/2 resistance: (ALS INHIBITORS)
Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS)

MUTATION: PROLINE 197 to THREONINE

Prickly Lettuce (Lactuca serriola) is a dicot plant in the asteraceae family. A single amino acid substitution from Proline 197 to Threonine has led to resistance to ALS inhibitors as indicated in the table below.

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Prickly Lettuce

Chemistry	Example	Resistance
Imidazolinones	Imazethapyr	Intermediate Resistance < 10 fold
Pyrimidinylthiobenzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidines	Chloransulam-methyl	Intermediate Resistance < 10 fold
Sulfonylaminocarbonyltriazolinone	Flucarbazone-Na	Not Determined

NOTES

REFERENCES

Preston, C., L. M. Stone, M. A. Rieger, and J. Baker (2006). Multiple effects of a naturally occurring proline to threonine substitution within acetolactate synthase in two herbicide-resistant populations of Lactuca serriola Pesticide Biochemistry and Physiology , 84 (3) : 227-235.

Two populations of Lactuca serriola L. with resistance to acetolactate synthase (ALS)-inhibiting herbicides were discovered in wheat fields at two locations more than 25 km apart in South Australia. Both resistant populations carried a single base change within a highly conserved coding region of the ALS gene that coded for a single amino acid modification within ALS. The modification of proline 197 to threonine resulted in an enzyme that was highly resistant (>200-fold) to inhibition by sulfonylurea herbicides and moderately resistant to triazolopyrimidine and imidazolinone herbicides. The herbicide-resistant ALS was also less sensitive to inhibition by the branched-chain amino acids valine and leucine. In addition, the resistant enzyme had a lower Km for pyruvate. However, extractable ALS activity was similar between resistant and susceptible plants. The substitution of threonine for proline 197 within ALS has multiple impacts on ALS enzyme activity in L. serriola that may influence the frequency of this resistant allele in the environment.