THE EFFECTS OF IRON-DEFICIENCY ON THE ATPASE AND FERRICYANIDE REDUCTASE ACTIVITIES OF PLASMA-MEMBRANE PURIFIED BY PHASE PARTITIONING FROM SUNFLOWER ROOTS

Young sunflower plants (Helianthus annuus L. cv. Topflor), grown in ir on (Fe)-free nutrient solution, developed Fe deficiency symptoms chara cteristic for dicotyledonous and non-graminaceous monocotyledons, such as chlorosis, reduced shoot growth, changes in root morphology, incre ased ferricyanide reductase activity and net proton extrusion. The fer ricyanide reductase activity of roots was low in the acidic pH range a nd increased with increasing pH, reaching maximal activity above pH 7. Five to ten mM Ca2+ and 0.25 mM NAD(P)H caused a 2- to 3-fold increas e in the reductase activity. Plasma membrane (PM) vesicles were purifi ed from the microsomal fraction (MF) of roots of Fe deficient and Fe s ufficient sunflower using an aqueous polymer two-phase system. Fe defi ciency induced an increase in NAD(P)H-ferricyanide oxidoreductase acti vity both in the microsomal (2-fold) and plasma membrane (3-fold) frac tions. ATPase activity in PM from Fe deficient roots was not significa ntly changed. These data demonstrate that the linkage between PM ATPas e and reductase systems occurs via changes in membrane polarization an d acidification rather than via direct coupling. However, the activity of the ATPase under physiological conditions may also be altered due to structural changes in root cells and tissues under Fe deficiency.