Effects of 2,4-dinitrophenol on membrane lipids of roots

Previous work has shown that the undissociated form of 2,4-dinitrophenol (DNP) increases the permeability of barley (Hordeum vulgare var. trebi) roots to ions. The present studies were undertaken to determine whether the effects of undissociated DNP were directly on membrane lipids. Relative amounts of the principal fatty acids from the lipids of barley root membranes were assayed as a function of DNP concentration, pH, and time of treatment under conditions similar to the previous studies of DNP effects on permeability. Undissociated DNP increases the proportions of palmitic and oleic acids and decreases linoleic and linolenic acids with no changes in the amounts of total fatty acids. The effects are immediate, as are the effects on permeability. Only the undissociated DNP is effective. Anionic DNP has no effect, although it is the major species taken up by the roots both at pH 5 and pH 7. DNP has no effect on respiration at either pH, indicating that undissociated DNP effects are on the membranes and not a general metabolic effect. The close parallelism between the effects of DNP on the composition of membrane lipids and on permeability suggests that the increase in permeability produced by undissociated DNP is due to a direct effect on the root membranes.