Cellular mechanisms influence differential glyphosate sensitivity in field bindweed (Convolvulus arvensis) biotypes

Abstract

Biotypes of field bindweed that vary in sensitivity to glyphosate were studied to determine the physiological or biochemical bases for these differences. Studies con ducted using whole plants and in vitro cultured shoots identified several potentially important differences between the most tolerant (biotype 4) and most susceptible (biotype 1) biotypes. Biotype 4 plants had greater 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS) activity and higher concentrations of phenolic compounds, indicating greater shikimate pathway activity than biotype 1. This may reflect a higher growth ability of biotype 4, as observed in shoot cultures.5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity in whole plants increased in all parts of biotype 4 by 7 d after a glyphosate treatment of 1.1 kg ae ha−1, whereas activities in biotype 1 plants did not increase at any time. However, this may not be the only mechanism of glyphosate tolerance because EPSPS activity in cultured shoots of both biotypes increased equally in response to glyphosate, even though biotype 4 shoots were able to survive and grow on a glyphosate-containing medium that inhibited growth of biotype 1 shoots. We propose that multiple mechanisms operating at a cellular/metabolic level combine to enable biotype 4 to tolerate higher glyphosate rates than biotype 1.