Uptake of systemic fungicides by maize roots

The absorption of nine benzimidazole derivatives and four thiophanates by excised maize roots was shown to be due to passive mechanisms because a. the temperature coefficient was low, b. anaerobic conditions or metabolic inhibitors had little or no effect, c. the rate of uptake was a linear function of external concentration, d. compounds of similar structure did not compete for absorption.For benzimidazole derivatives, we observed a very rapid initial uptake which reached a maximum after one or two hours; this saturation did not occur with thiophanates.The effect of pH on the root absorption of benzimidazole derivative indicates that molecular (or unionized) forms of these amphoteric compounds were taken up preferentially; the behaviour of thiophanates was different.As observed with other pesticides, root absorption was greater for lipophilic than for lipophobic substances and in our experiments the rate of uptake of fungicides was well correlated to their partition coefficient in an octanol/ water system at pH 6.5.Generally, the various fungicides were taken up to the same extent all along the length of the roots.