Fig. 2. Biochemistry of the FC receptor in Xenopus tissue. Xenopus laevis embryos possess a Fusicoccin-binding site whose properties differ from that of the classical higher plant Fusicoccin receptor. (A) Saturation analysis of specific binding of [³H]9'-nor-fusicoccin-8'-alcohol to plasma membranes of barley roots (black circle) and embryo cytoplasmic protein extract (white circle). Data was fitted using the equation describing a rectangular hyperbola. The resulting coefficients gave rise to values for the K_D and B_max, which are referred to in the main text. The data are expressed as the means±s.e.m. of a representative experiment. (B) Competitive binding experiments with [³H]9'-nor-fusicoccin-8'-alcohol and unlabelled Fusicoccin A. Barley root plasma membranes were incubated with 1 nM radioligand (black circle) and embryo cytoplasmic protein extract was incubated with 4 nM radioligand (white circle). The data was fitted using the equation describing a sigmoidal curve of 3 parameters (Sigmaplot, SPSS scientific).