PHYSIOLOGICAL-EFFECTS OF COPPER ON IRON ACQUISITION PROCESSES IN PLANTAGO

In Plantago lanceolata L. the effect of Cu(II) additions to the nutrie nt solution on root-associated Fe(III) reductase was studied in a fact orial design with different Cu(II) and Fe(III) concentrations. Iron st arvation resulted in approx. an eightfold increase in root Fe reductio n at the level of intact plants and twofold enhancement in the specifi c activity of both NADH-linked FeEDTA reductase and H+-ATPase in isola ted root plasma membrane vesicles. In plants exposed to low (0.3-0.7 m u M) Cu and suboptimal Fe levels, reduction activity at the root surfa ce was further increased and associated with more severe interveinal c hlorosis than plants grown in Cu-free medium. In Fe-sufficient plants, withholding Cu over a prolonged period slightly enhanced the reductio n activity. Addition of high (5 mu M) Cu concentrations to Fe-free med ium inhibited the induction of the physiological responses by Fe-defic iency stress. In plants without Fe supply but with adequate Cu supply, short-term application of 5 mu M CuSO4 completely inhibited the reduc tion activity. Neither incubation of the plasma membrane Vesicles befo re measurement nor incubation of intact plants with Cu before isolatio n caused a significant decrease in reductase activity. The results are interpreted as indicating different mechanisms underlying Cu-induced alterations in iron nutrition.