gradient can be roughly linearized in exponential units, and in a decreasing value from distances to the epicenter, one can replot the data using R versus e^-d.This leads to typical biphasic dose/effects relationships (Figures 2A and 2B) as encountered in ligand-receptor interactions (Bounias & Pachéco, 1972; Sanchez & Changeux, 1966) (Figure 2C.)

The equation of such a phenomenon is rather complex (Bounias, 1987), but highly representative of a number of toxicological stresses in plants (Stevens & Merril, 1985) (Figure 2D).

Threonine and serine exhibit a similar response, except that concentrations reach an intermediate minimum instead of a maximum value (Figures 3A and B in small frames).

In this case, plotting Ro-R versus e^-d gives curves similar to those on Fig. 2, except that values reach zero for e^-d= 1 (Figures 3A and 3B). Similar features encountered under the stress of toxins or electromagnetic parameters are shown on Figures 3C and 3D, respectively.

Alteration of Functional Relationships in Connection With the UE

It has been shown that the algebraic form of the relations between two biochemical parameters may prove to be a sensitive way for evidencing stress effects (Bounias, 1975; Bounias et al.,1987). This might allow the characterization

Fig. 2. Biphasic dose/effect relationships: A and B resp. = Raffinose and Ribose-like concentrations versus e -d. C = control of Barley leaves phosphatases by L. leucine (Bounias & Pachéco, 1972). D = control of Lettuce roots growth (mm) by solstitiolide (µ/g). (Stevens and Merril, 1985)