Quantitative GUS activity as a function of applied magnetic field. The amount of GUS activity, as measured by biochemical/fluorometric procedures, is plotted as a function of applied magnetic field. Each data point represents the average of three plants and the uncertainty limits are given by the standard deviation. Three data sets were collected at the NHMFL and one was obtained in a UF superconducting solenoid capable of reaching 9 Tesla. Nonparametric statistical methods have been used to test the hypothesis about an association between the GUS activity and the magnetic field. For the leaves (a), the Spearman correlation coefficient of 0.58 (P = 0.001) indicates that there exists a significant association between these two variables. For the roots (b), the Spearman correlation coefficient of 0.40 (P = 0.033) suggests a somewhat weaker association. A statistical model was formulated, hypothesizing a log-normal relationship for the effect of the magnetic field on the level of GUS activity (see text). The data for the leaves (a) were analyzed using nonlinear weighted least squares, and the result is plotted as the black line, with the 95% confidence limits given by the grey lines.