ACTIVITIES OF PLASMA MEMBRANE-BOUND ENZYMES ISOLATED FROM ROOTS OF SPRUCE (PICEA-ABIES) GROWN IN THE PRESENCE OF ALUMINUM

The effect of aluminium on plasma membrane-bound enzymes and ion uptak e was studied with spruce cuttings (Picea abies Karst.) grown in nutri ent solution, pH 4.2, for 5 weeks. The H+-ATPase and glucan synthase I I activities of isolated root plasma membranes were inhibited by the p resence of aluminium during growth (0.1-3 mM), with glucan synthase II being more sensitive than the ATPase. The active K+-uptake obtained w ith intact roots was also inhibited by aluminium, whereas the passive uptake was stimulated ca 4-fold by moderate amounts of aluminium (0.1 mM). The uptake of Ca2+ (passive) was severely inhibited at all extern al aluminium concentrations tested. Experiments were also performed wi th aluminium added during the assay, or in preincubations of isolated plasma membranes. Again, the glucan synthase II activity was severely inhibited by aluminium. There were no signs of adaptation, i.e., the a ctivities with plasma membranes from cuttings given aluminium during g rowth, were equally sensitive as the control. The aluminium additions in vitro were at pH 6.5 (ATPase) or 7.25 (glucan synthase II) indicati ng that for the enzymes studied, aluminium can be toxic although the p H is neutral.