Safeners for chlorsulfuron on maize (Zea mays L.)

Introduction Chlorsulfuron inhibits acetolactate synthase (ALS), a key enzyme in plants needed in the biosynthesis of the branched amino acids isoleucine, leucine and valine. Maize is a susceptible crop to the action of this herbicide. Objectives This article examines the synthetic compound 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine as a possible safener for chlorsulfuron in maize (Zea mays L. cv. Kneja 530). Methods Commercial herbicide safener, 1,8-naphthalic anhydride, was used as a standard. Maize seeds were impregnated with 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine or naphthalic anhydride by soaking for 5 h in aqueous solutions, followed by a herbicide treatment for 5 h. Plants were grown as water cultures. Results Changes in growth and in specific activity of acetolactate synthase were determined 8 and 12 days after the treatment. Shoot length and fresh weight of maize plants treated with 10(-5) M chlorsulfuron were inhibited 59% and 52%, respectively, compared with untreated plants, whereas pretreatment with 5 x 10(-4) M 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine and naphthalic anhydride reduced these inhibitions. Moreover, the decrease in the root growth caused by chlorsulfuron alone was almost completely reversed by 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine. The specificity of naphthalic anhydride and 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine's action on acetolactate synthase was supported by the lack of effect on the enzyme activity in vitro. However, pretreatment of seeds with both safeners overcomes chlorsulfuron-induced inhibition of acetolactate synthase activity in leaves and roots, 8 and 12 days after treatment. Conclusion Our data showed that the synthetic compound 1-(4-fluorophenylthiocarbamoyl)-4-methylpiperazine was a more active herbicide safener in the roots whereas the naphthalic anhydride, in the leaves.