Biochemical Evidence for Two Forms of Acetohydroxyacid Synthase in Daucus carota L. Cell Lines Selected for Chlorsulfuron Resistance

Biochemical characterization of acetohydroxyacid synthase (EC 4.1.3.18) has been carried out in Daucus carota L. cell cultures, in both wild type and those selected for chlorsulfuron resistance. Two forms of acetohydroxyacid synthase exhibiting different sensitivity to chlorsulfuron and leucine inhibition were resolved by anion exchange chromatography. In those carrot cell cultures selected for chlorsulfuron resistance, acetohydroxyacid synthase gene amplification has been shown and an increased level of the enzymatic form that is less sensitive to chlorsulfuron inhibition and almost insensitive to leucine feedback inhibition was observed. Further characterization of acetohydroxyacid synthase activity from the selected cells provided evidence that the two forms differed in their apparent molecular mass and subunit composition.