Isolation of molybdenum cofactor defective cell lines of Nicotiana tabacum

Summary Thirty-nine chlorate resistant cell lines were isolated after plating ethylmethane sulphonate treated allodihaploid cells of Nicotiana tabacum cv. Xanthi on agar medium containing 20 mM chlorate. Thirty-two of these cell lines grew as well on nitrate medium as on amino acid medium and three other cell lines grew well on amino acid medium but poorly on nitrate medium. Four other cell lines, 042, P12, P31 and P47 which could grow on amino acid medium, but not on nitrate medium, were examined further. They lacked in vitro nitrate reductase activity but were able to accumulate nitrate. All lines possessed nitrite reductase activity. Lines 042, P12, and P31 had a cytochrome c reductase species which was the same size as the wild type nitrate reductase associated cytochrome c reductase species, whilst the cytochrome c reductase species in line P47 was slightly smaller. All four lines lacked xanthine dehydrogenase activity and neither nitrate reductase nor xanthine dehydrogenase activity was restored by subculture of the four lines into either nitrate medium or glutamine medium supplemented with 1 mM sodium molybdate. These four lines are different from other molybdenum cofactor defective cell lines so far described in N. tabacum and possess similar properties to certain other cnx mutants described in Aspergillus nidulans.