Abstract
Six chlorate-resistant (CR) cell lines were established from survivors after plating mutagenized and non-mutagenized cells of Kp20, a Paeonia haploid cell line, onto solid medium containing 30mM KClO3 and amino acids as the sole nitrogen source (AA-chlorate medium). Five millimolar N-ethyl-N-nitrosourea (ENU) was used as the mutagen. None of the 6 CR lines grew on medium containing nitrate as the sole nitrogen source (NO3-medium). Of these CR lines, 5 completely lacked in vivo nitrate reductase (NR) activity and one showed low (about 11% of that of the wild type) NR activity. In all CR lines except for one, the percentage occupied by haploid cells increased to 83-95% compared with 73% in the wild type. This suggested that mutation may have occurred to advantage in the haploid cells.
