LEAKAGE OF PHENOLIC-COMPOUNDS FROM PLANT-ROOT - EFFECTS OF PH, CA2+ AND NACL

The effects of pH on leakage of phenolic compounds from roots or root segments of rose plants (Rosa indica major), beans (Phaseolus vulgaris) and African lilies (Agapanthus africanus) were investigated by incubation of roots in solutions of potassium phosphate buffer of various concentrations at pH 6.2 or 7.6. The leakage of phenols from the roots into buffer was affected by the buffer concentration and the duration-of root incubation in the buffer. However, the leakage of phenols from the roots into the pH 6.2 buffer was markedly lower than into the pH 7.6 buffer. This difference was also present when, following incubation in the buffer, the roots were transferred into water. The leakage from roots was suppressed by addition of calcium to the buffer solution. However, a lower concentration of calcium was required for suppression of leakage at pH 6.2 than at pH 7.6. Salt-induced leakage of phenols was reduced by 50% when the pH of 100 mM solution was adjusted to 6.2 with 20 mM buffer compared with the leakage imposed by NaCl adjusted to pH 7.6. The leakage of electrolytes from rose root segments, following exposure to sodium phosphate pH 6.0, was also lower than that of segments exposed to the pH 7.6 buffer. The possibility of direct high pH effects in the root environment on the root cell membrane function, as well as the effects of pH on solubility and uptake of ions, is discussed.