influcnce of naphthalic anhydride and I-Aminobenzotriazole on maize resistance to herbicides-Secondary metabolism responses

ABSTRACT

Dry weight of maize shoots was significantly decreased following treatments with alachlor, metolachlor and atrazine; more reduction was observed with atrazine. The presence of naphthalic anhydride [NA] relieved these reductions whilst I-aminobenzotriazole [ABT] showed cumulative effects. Meanwhile activities of phenylalanine ammonia lyase [PAL,], tyrosine ammonia lyase [TAL] and chalcone isomerase [CI] were significantly increased; alachlor seemed the most inductive. The presence of NA counterbalanced the enhanced activities whereas ABT showed much reduction. Phenolic compounds and anthocyanin significantly increased by alachlor and metolachlor while atrazine had no effect. These increased levels became comparable to that of controls by NA but significantly diminished by ABT. The responses of PAL, TAL, and Cl preceded that of phenolics and anthocyanin confirming the controlling role of these enzymes. Moreover, these findings reveal the occurrence of an induced stress status. The counterbalancing action of NA on herbicide effects indicates the retraction of these conditions, might be due to herbicide detoxification. In contradistinction, ABT reduced these levels suggesting more decreases in enzyme concentrations probably because of the sinking of herbicide degradation through the inhibition or P450s. So a protraction of herbicide persistence, and consequently increased the phytotoxicity, could occur within the plant