Unique cellular effect of the herbicide bromoxynil revealed by electrophysiological studies using characean cells

In a previous paper, we proposed that the primary action of the herbicide bromoxynil (BX; 3,5-dibromo-4-hydroxybenzonitrile) is cytosol acidification, based on the fact that bromoxynil induced the inhibition of cytoplasmic streaming and cell death of Chara corallina in acidic external medium (Morimoto and Shimmen in J Plant Res 121:227-233, 2008). In the present study, electrophysiological analysis of the BX effect was carried out in internodal cells of C. corallina. Upon addition of BX, a large and rapid pH-dependent depolarization was induced, supporting our hypothesis. Ioxynil, which belongs to the same group as bromoxynil, also induced a large and rapid membrane depolarization in a pH-dependent manner. On the other hand, four herbicides belonging to other groups of herbicides did not induce such a membrane depolarization. Thus, BX has a unique cellular effect. The decrease in the electro-chemical potential gradient for H(+) across the plasma membrane appears to result in inhibition of cell growth and disturbance of intracellular homeostasis in the presence of BX.