Comparative studies between glyphosate-adapted and non-adapted carrot-cells in tissue culture

Biochemical changes of glyphosate-adapted carrot cells in tissue culture were characterized and the inhibition sites of glyphosate were surveyed. Concentrations of glyphosate associated with fifty percent growth inhibition were 2mM and 0.2mM in the adapted and non-adapted cells, respectively. Although an abnormal accumulation of shikimic acid was observed in both adapted and non-adapted cells, the amount in the latter was higher than in the former (Fig. 1 and Table 1). By the addition of three kinds of aromatic amino acids, phosphoenolpyruvate and δ-aminolevulinic acid at the same time in the adapted and nonadapted cells, the growth was reversed and also the abnormal accumulation of shikimic acid was reduced (Figs. 2, 3). Activities of the enzymes 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase) and 3-deoxy-D-arabinoheptulosonate-7-phosphate synthase (DAHP synthase) were 10.7-fold and 3.6-fold higher, respectively, in the adapted cells compared with the non-adapted ones. Both EPSP synthase and DAHP synthase in the adapted and non-adapted cells were sensitive to glyphosate. It is thus suggested that the glyphosate-adapted cells, because tolerant to glyphosate due to the increase of the activities of EPSP synthase and DAHP synthase, but not due to a decrease in the susceptibility to glyphosate (Table 2, Fig. 4 and Fig. 5).