Increased activity and reduced sensitivity of glutamine synthetase in glufosinate‐resistant vetiver ( Vetiveria zizanioides Nash) cells

Vetiver ( Vetiveria zizanioides Nash) cells derived from an inflorescence were cultured in a modified N6 liquid medium supplemented with 10 µ m 2,4‐D and 10 m m proline. Exponentially growing cell suspensions were subcultured with a selection medium containing glufosinate (ammonium dl ‐homoalanin‐4‐yl(methyl)phosphinate). The glufosinate‐resistant cells which can grow in a medium containing 5 × 10 −5 M glufosinate was selected by a stepwise selection, and its I 50 value was determined to be 4.2 × 10 −5 M. The growth of susceptible cells was inhibited by lower concentrations of glufosinate and its I 50 value was 2.5 × 10 −7 M. This indicated that the selected cells were 170‐fold resistant compared with the susceptible cells. Glutamine synthetase (GS) activity of the resistant cells was twice as high as that of the susceptible cells. The I 50 values of glufosinate were 3.2 × 10 −5 M and 9.0 × 10 −7  M for GS from the resistant and susceptible cells, respectively. The accumulation of ammonia caused by GS inhibition was higher in the susceptible cells. Absorption of [3,4– 14 C]glufosinate was not significantly different between the resistant and susceptible cells. Both cell types did not metabolize glufosinate. These results suggest that the resistance of the selected vetiver cell suspension to glufosinate is mainly due to increased GS activity and its decreased sensitivity to the herbicide.