Biochemical mechanisms of field bindweed (Convolvulus arvensis L.) biotype tolerance to the herbicide glyphosate (N-(phosphonomethyl)glycine);

Five biotypes of field bindweed (Convolvulus arvensis L.) have been identified. Response to the herbicide glyphosate (N-(phosphonomethyl)glycine) varies with biotype. Differential response cannot be fully accounted for by variation in herbicide absorption/translocation. Studies showed that cultured plant cells had patterns of response to glyphosate similar to that observed at the whole plant level. A cell line 4S was selected for tolerance to glyphosate. Exposure of the biotypes in cell suspension culture to their respective I$\sb{50}$ glyphosate concentrations resulted in enhanced EPSPS activity. Immunoblots of EPSPS from 4S cells showed a close correlation with increased activity levels. Susceptible biotype 1 had a single protein band at 48 kDa (EPSPS) but, biotypes 4 and 4S exhibited a second band in this region. Biotypes 1 (susceptible) and 4 (tolerant) plants both survive glyphosate applied at 1.12 kg ha$\sp{-1}$. Biotype 1 exhibits a rapid increase in EPSPS activity followed by a return to basal levels. Biotype 4 shows a prolonged linear increase in EPSPS activity. Immunoblots of EPSPS show a linear increase with time for both biotypes. At 2.24 kg glyphosate ha$\sp{-1}$ only biotype 4 plants survive. Immunoblots of biotype 1 EPSPS show an initial increase prior to a rapid drop. At the end of the observation period biotype 4 EPSPS levels are only 1.1-fold greater than prior to treatment, corresponding to a 2.1-fold increase in activity. As observed in the tolerant cell lines, biotype 4 plants exhibit two bands in the 48 kDa region