Uptake of [¹⁴C]-8-Azido-N⁶-Benzyladenine, a Radioactive Photosensitive Cytokinin, by the Cells of the Moss Funaria hygrometrica L

Abstract

High affinity sites for cytokinins that appeared to have some of the properties expected for hormone receptors have been shown to occur in tobacco cells (Sussman and Kende, 1978) wheat germ (Fox and Erion, 1975; Polya and Davies, 1978; Moore, 1979) and pumpkin cotyledons (Roussell and Fox, 1979). Low affinity sites for cytokinins were also observed in much higher frequency. From their characteristics it was proposed that they were unrelated to the biological action of the hormone. All these cytokinin-binding sites have been studied with subcellular fractions from plant homogenates. Since it is now known that cytokinins have a strong tendency to bind to any substrate, even unrelated to biological materials, such as talc (Sussman and Kende, 1978; Gardner et al., 1978), the question then arose of whether the observed ratio of low affinity sites to high affinity sites was true or had been favored during the preparation of the subcellular fractions, thus hampering any attempt to characterize cellular receptors for cytokinins.