ALUMINUM EFFECTS ON TRANSMEMBRANE POTENTIAL IN ROOT-CELLS OF SPRUCE IN RELATION TO PH AND GROWTH TEMPERATURE

The immediate effect of aluminum (Al) on the transmembrane-electrical potential (PD) in root cells of spruce (Picea abies L. cv. Emmaboda) w as studied after growth of spruce at different temperatures. The PD wa s determined with microelectrodes inserted into the vacuoles (PDv) or into the cytoplasm (PDc) of root cells of intact seedlings. After grow th of the seedlings at 17 degrees/21 degrees C (night/day), addition o f aluminum chloride (50-100 mu M) to the root medium at external pH 4. 0 or 5.0 only slightly affected the PD. However, addition of Al at pH 6.5, caused a hyperpolarization of PDv and a depolarization of PDc. Re moval of Al from the root medium caused a depolarization of PDv. After pregrowth of spruce plants for one week at 10 degrees C, the PDv, mea sured at pH 5.0 and 21 degrees C, was immediately depolarized and then hyperpolarized upon addition of 100 mu M Al. After removal of Al from the root medium the resting PDv was depolarized to a less negative va lue than before the treatment with Al. Thus, the effect of Al on PD of root cells both depends on the pH of the root medium and the temperat ure during cultivation. After growth at 10 degrees C, which is more re levant for spruce, the effect of Al on PD is stronger than after growt h at 21 degrees C.