Effects of Calcium, Magnesium, and Phosphate on Glyphosate Absorption by Cultured Plant Cells

Effects of several inorganic ions on short-term glyphosate absorption by cultured plant cells were determined by measuring the glyphosate content of cells exposed to inorganic salts in a 0.01-mM glyphosate solution buffered at pH 5.7. Within 10 min, glyphosate absorption by potato and velvetleaf cells was stimulated about equally by 1.5 mM CaCl 2 or 1.5 mM MgCl 2 but was not affected by 1.5 mM KCl. Glyphosate absorption by both species increased linearly with log 10 CaCl 2 concentration; for velvetleaf cells, the response was greatest for CaCl 2 concentrations greater than 0.2 mM. Over time of absorption, glyphosate concentration within velvetleaf cells approached an asymptote. Addition of 0.1 mM KH 2 PO 4 inhibited glyphosate absorption by potato cells in the presence or absence of Ca 2+ and Mg 2+ salts; all other K + salts tested had no effect. Glyphosate absorption by potato, velvetleaf, soybean, corn, and rice cells was stimulated by 5.0 mM CaCl 2 but was inhibited by 0.1 mM KH 2 PO 4 in the presence of 0.05 or 5.0 mM CaCl 2 .