Inhibition of fusicoccin‐stimulated K + /H + transport in root tips from maize seedlings pretreated with Chlorsulfuron

Fusicoccin (FC)‐stimulated K + ( 86 Rb) uptake and proton extrusion of maize ( Zea mays ) root apical segments were inhibited by pretreatment of 4‐day‐old seedlings with the herbicide Chlorsulfuron. In the range of Chlorsulfuron concentrations 0.01‐10 mmol m −3 , the percentage of inhibition was 15% at 0.01 mmol m −3 and progressively increased with Chlorsulfuron concentration up to 60% at 10 mmol m −3 . At the maximum concentration tested (10 mmol m −3 ), the inhibition was evident after 1.5 h of pre‐treatment. The binding of FC to microsomal fractions of root segments from Chlorsulfuron‐pretreated seedlings was inhibited by 30%. It is suggested that Chlorsulfuron causes an alteration at the plasmalemma level involving the FC binding sites. The ineffectiveness of Chlorsulfuron in inhibiting FC‐stimulaled K + uptake when administered to excised segments, while inhibiting the enzyme acetolactate synthase, pointed out by Ray (1984) as the site of action of Chlorsulfuron in pea plants, suggests that the observed inhibition of K + uptake and H + extrusion is not induced by Chlorsulfuron inhibition of this enzyme. An alternative site of action of Chlorsulfuron is hypothesized in maize plants.