Acetohydroxyacid Synthase GENE Amplification Induces Clorsulfuron Resistance in Daucus Carota L.

Abstract

In vitro cell selection was used to isolate Daucus carota L. cell cultures resistant to increasing concentrations of the sulfonylurea herbicide chlorsulfuron (CS). The stepwise scheme produced cells 300-fold more resistant to CS than the wild type. CS resistance was stably maintained after several passages in the absence of selective pressure. During the selection the specific activity of acetohydroxyacid synthase (AHAS), the sulfonylurea target enzyme, increased along with resistance. Dot-blot analysis carried out on the genomic DNA of the selected cultures, using a heterologous AHAS probe, revealed that AHAS gene copy number also increased gradually. Gene amplification was considered responsible for the overexpression of AHAS activity and the consequent CS resistance. Morphogenetic ability of the selected cultures was not affected since plants were regenerated from the resistant cell lines. In several cases the resistant trait was maintained at the whole plant level.