Effect of glyphosate on the activity of DAHP synthase isozymes in callus cultures of groundnut (Arachis hypogaea L.) selected in vitro

Two isozymes of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHP synthase or DS, EC 4.1.2.15) from the callus cultures of Arachis hypogaea L . were resolved by DEAE cellulose column chromatography and characterized u sing selective assays based on divalent cation requirements and regulation by the end-product amino acids. The total extractable activity of DAHP synt hase did not show any change in the glyphosate sensitive and tolerant cell lines when compared to 5-enolpyruvylshikimate-3-phosphate synthase (EPSP sy nthase, EC 2.5.1.19), the known target of inhibition by glyphosate. However , the activities of both, DAHP synthase and EPSP synthase were inhibited by glyphosate in vitro. The inhibitory effects of glyphosate on the activitie s of (a) EPSP synthase and DAHP synthase, and (b) isozymes of DAHP synthase , have been compared. The data indicate that the Co2+ dependent isozyme of DAHP synthase is a putative target for the action of glyphosate in A. hypog aea.