Interaction between electron transport at the plasma membrane and nitrate uptake by maize (Zea mays L.) roots

In the present study nitrate uptake by maize (Zea mways L.) roots was inves tigated in the presence or absence of ferricyanide (hexacyanoferrate III) o r dicumarol. Nitrate uptake caused an alkalization of the medium. Nitrate u ptake of intact maize seedlings was inhibited by ferricyanide while the eff ect of dicumarol was not very pronounced. Nitrite was not detected in the i ncubation medium, neither with dicumarol-treated nor with control plants af ter application of 100 ELM nitrate to the incubation solution. In a second set of ex experiments interactions between nitrate and ferricyanide were in vestigated in vivo and in vitro. Nitrate (1 or 3 mM) did neither influence ferricyanide reductase activity of intact maize roots nor NADH-ferricyanide oxidoreductase activity of isolated plasma membranes. Nitrate reductase ac tivity of plasma-membrane-enriched fractions was slightly stimulated by 25 muM dicumarol but was not altered by 100 CIM dicumarol, while NADH-ferricya nide oxidoreductase activity was inhibited in the presence of dicumarol. Th ese data suggest that plasma-membrane-bound standard-ferricyanide reductase and nitrate reductase activities of maize roots may be different. A possib le regulation of nitrate uptake by plasmalemma redox activity as proposed b y other groups, is discussed.