Effect of Glyphosate on Membrane Permeability in Red Beet (Beta vulgaris) Root Tissue

When discs of red beet (Beta vulgarisL.) root were immersed in various concentrations of glyphosate [N-(phosphonomethyl)glycine] either in phosphate (pH 6.8) or citrate (pH 6.2) buffer, no efflux of betacyanin occurred even after 1 week. This suggests that glyphosate had little or no effect on membrane permeability. When beet discs were immersed in distilled water containing glyphosate, the betacyanin efflux increased with time and concentration. Measurement of pH indicated that the solutions were strongly acidic at first, but tended to approach a pH of 6.0 over 8 h, after which time betacyanin efflux slowed down or stopped. The tissue was able to buffer the solutions sufficiently to prevent further efflux. When tissue discs were immersed in a series of citrate buffer ranging from pH 3 to 6.2, efflux occurred at pH 3 and slightly at pH 6.2. Efflux was not altered significantly with the addition of glyphosate.