Buffering effects of benzimidazole in absorption of potassium by excised barley roots

Benzimidazole (BZ) enhancement of ion uptake was recently reported by Klingensmith (11) and Klingensmith and Norman (12). Their experiments were conducted with excised barley roots at rather high root to solution ratios (7) without added buffer. Potassium uptake was determined by difference, without the complications due to the presence of other ions, but in such systems there is apparently a progressive increase in acidity during the experimental period, which results in a change in the rate of uptake of the cation. The effect of hydrogen ion concentration on K+ absorption by excised barley roots has been discussed in detail by Jacobson et al. (7, 8, 9) and by Nielsen and Overstreet (14). These workers have reported that the absorption of K+ decreases markedly in the pH range from 6 to 4 and that tissue injury probably occurs at lower pH values followed by loss of cellular constituents to the external medium. Hofmann (6) in a discussion of the chemical properties of the benzimidazoles points out that these compounds are amphoteric. The acidic property of BZ is reflected in its ability, under quite specific conditions, to form rather stable salts and complexes with certain metals, such as Ag, Cu, Cd, Ni, Co, Hg, and Zn. In addition, crystalline BZ salts of Li, Na, K, and Ba have been prepared; however, these are very unstable and hydrolyze upon exposure to water with regeneration of BZ. Substitution of the imino hydrogen on the imidazole ring eliminates the acidic property. The basic characteristic of BZ results from the ability of the pyridine (tertiary nitrogen) nitrogen of the imidazole ring to accept a proton and thus become ionized as a cation. In this respect, BZ is a weak base that is able to act as an effective buffer. The present study was conducted to investigate further the apparent enhancement of the uptake of K+ by BZ in the light of the recognition of the strong buffering property of this compound.