Abstract: Suspension culture cells initiated from haploid Datura inoxia seedlings were transferred on a paper and were treated with UV. The nitrate reductase (NR) deficient mutants were isolated by selection for chlorate resistance. The NR activity could not be recovered, even though the mutants were transferred into the medium without selective pressure for three years. Isoelectrofocusing gel showed that the gene of NR was not destroyed by the treatment of UV. The mutant cells were defective in the cytokinin binding protein. The cytokinin binding-protein was isolated from wheat seedlings with the aid of 6BA immobilized on the epoxy-sepharose colunm. An addition of binding-protein, together with 6BA, to the medium for synthesis of RNA in vitro brough about an activation of RNA-polymerase. In wild type cells the NR activity was accelerated by the addition of cytokinin to the culture medium. In contrast, cytokinin was of no effect on the synthesis of NR in mutant cells. It is, therefore, suggested that the effect of cytokinin on the RNA synthesis and NR formation was regulated by the content of cytokinin binding-protein in Datura inoxia mutant cells.

Key words: 6-Benzyladenine, Binding protein, Nitrate reductase, Datura inoxia