Action of soil humic matter on plant roots: Stimulation of ion uptake and effects on(Mg 2++K +) ATPase activity

Abstract

The effects of soil humic matter on the uptake of ions by oat roots and on the (Mg 2++K +) ATPase activity, responsible for energy transduction for ion transport at cell membrane, were studied. Four-day-old roots treated for 8 h with unfractionated humic solution (50 μg org C × ml −1) took up K + and SO 4staggered −2 ions at rates, respectively, 33% and 106% higher than the controls. Similar effects were caused by humic and fulvic acids, and by the hot-acid soluble and hot-acid insoluble fractions prepared from humic acids. At org C concentration higher than 1 μg ml −1, the humic extract inhibited both Mg 2+ dependent and K +-stimulated ATPase activities of microsomes isolated from roots. At 0.33–1 μg org C ml −1, the Mg 2+-dependent activity was inhibited, whereas the activity stimulated by K + increased. Humic acids and the acid-insoluble fraction inhibited the ATPase activity more than fulvic acids and the acid-soluble fraction. Preliminary results of SDS - PAG electrophoresis of membrane proteins showed two polypeptides associated with membrane of humus treated roots, which where absent in the control. Differences between the two phenomena and structure-activity relationships will be discussed.