BIOCHEMICAL AND GENETIC-CHARACTERIZATION OF 5-FLUORO-2'-DEOXYURIDINE-RESISTANT MUTANTS OF ARABIDOPSIS-THALIANA

Two independently isolated 5-fluoro-2'-deoxyuridine (FUdR)-resistant m utant lines of Arabidopsis thaliana (L.) Heynh., FUD-1 and FUD-2, were identified by screening M2 populations of ethylmethane-sulfonate-muta genized seeds. The resistance was found to be due to single, recessive , nuclear gene mutations. Genetic complementation tests indicated that these two mutations were in the same gene locus, which was designated fur1, and mapped to linkage group four of Arabidopsis. Enzyme assays indicated that the mutants were not defective in thymidine-kinase acti vity. Greatly reduced concentrations of intracellular H-3 were detecte d in fur1/fur1 plants compared with the wild type after incubation of wild-type and resistant plants in a medium with [H-3]FUdR, indicating that either reduced uptake of FUdR or enhanced efflux of FUdR metaboli tes was the major reason for FUdR-resistance. fur1/fur1 plants also ha d significantly decreased uptake of thymidine and uridine compared wit h the wild type but no difference was found in the uptake of adenosine , guanosine, thymine, uracil or amino acids. It is suggested that the transport system affected in the fur1/fur1 mutants is one specific to pyrimidine nucleosides.