Fig. 3. Effects of CaCl₂ and MgCl₂ concentrations in the reaction mixture on the activity of fructokinase extracted from pollen grains (A) and anther tissue (B). The dashed line with open circles represents the effect of CaCl₂ in the presence of 0·5 mm MgCl₂. Data are means (n = 5) ± s.e. Each assay mixture contained 20 µg protein.