Root Permeability as Affected by Picloram and Other Chemicals

The effects of picloram (4-amino 3,5,6-trichloropicolinic acid) and several other chemicals on root permeability were studied. Initially, effects on cell permeability were investigated by measuring the betacyanin efflux from red beet (Beta vulgaris L.) root sections. Picloram solutions ranging from 10^-3M to 10^-6M had no significant effect on betacyanin efflux when compared to controls. Similar results were found for 10^-4M and 10^-5M 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 10^-4M 2,4-dichlorophenoxyacetic acid (2,4-D) and 10 μl/l of ethylene. Compounds that caused significant pigment leakage were 10^-4M and 10^-5M phenylmercuric acetate (PMA), 10^-3M and 10^-4M 2,4-dinitrophenol (DNP), 10^-3M and 10^-4M 2,4,5–trichlorophenoxyacetic acid (2,4,5-T) and 10^-3M 2,4-D. The effects of picloram on root permeability were also studied with bean plants (Phaseolus vulgaris L. cv. Black Valentine) grown in nutrient solution under controlled environmental conditions. Roots treated for 3 hours with 10^-5M picloram showed no significant electrolyte leakage as determined by conductivity measurements of the root-bathing solution over a period of 52 hours. When bean plants were root-trated for 3 hours with 10^-5M, and 10^-7M picloram and then decapitated, increased stem exudation by the treated plants as compared to controls was observed. Xylem exudate of the teated plants also showed increased electrolytic conductivity. The increased exudation rate accompanied by increased conductivity indicates that picloram has little effect on root cell membrane integrity, appears not to act as a metabolic inhibitor in the root system, and in some way stimulates salt secretion into the xylem.