Figure 4

Dixon plot of endogenous GUS activity measured in Arabidopsis leaf extract. The plot is inferred from the data reported in the annexed table. These, in turn, are extrapolated from the experimental values reported in figure 3B. C indicates the extract concentration. In order to produce data suitable for the Dixon plot (refer to the Results section and Additional Material for further description), the measured reaction rates were corrected by the dilution factor (i.e. the reciprocal of the extract concentration). The reciprocals of the obtained values (C/Vm) were plotted versus the relative extract concentration, which coincides with the relative inhibitor concentration (As explained in Figure 3B). The intercept of the trend line provides the uninhibited activity in the undiluted extract, thus reported for C = 1 in the table. Uninhibited rates (Vc) at the extract dilutions used in the experiment are deduced by multiplying the latter value by the extract concentration; the resulting values are reported in italics in the table. Finally, the inhibitory capacity (I%) at each dilution can be deduced by comparison between the uninhibited reaction rates and the experimental values (data to Figure 3B), and it is here reported as percentage of inhibition. In this respect, when C = x = 1 (i.e. in the undiluted extract), the inhibited reaction rate corresponds to the reciprocal of the y value in the trend line equation, which provides the value (i.e. 15.2) from which to infer the percentage of inhibition in the undiluted extract (28.9%). Reaction rates are expressed as picomoles of MU produced per minute per milligram of protein of the undiluted extract.