Effects of fusaric Acid on tomato root hair membrane potentials and ATP levels.

Using standard microelectrode techniques, we measured the effects of fusaric acid (FA) on the membrane potential of tomato (Lycopersicon esculentum Mill. cv New Yorker 870) incipient root hair cells. At pH 5.3, FA caused a hyerpolarization, the magnitude of which increased with FA concentrations from 0.05 to 0.50 millimolar. A depolarization followed, the rate and magnitude of which increased with the concentration of FA and exposure to FA. Partial repolarizations occurred after exposures to 1.0 millimolar FA for less than 8 to 10 minutes, after longer exposures to lower FA concentrations, or after longer exposures to 1.0 millimolar FA in a less concentrated nutrient solution. The amount of ATP in tomato root tips decreased by about 85% after incubation for 80 min in 1.0 millimolar FA.At pH 7.2 and 8.2, the depolarization caused by an 8-minute exposure to 1.0 millimolar FA was immediate and much more rapid than at pH 5.2 and 6.3, but its magnitude was not as great. At pH 6.3, 7.2, and 8.2, the depolarization was at least partially reversible. The data are consistent with FA having at least three effects that elicited changes in tomato root cell electrical potential differences between the cell's interior and the external solution.