Relationships between nitrate uptake and nitrate reductase activity in Cucumis sativus L., roots

Anti-NR IgG fragments obtained after papain digestion of polyclonal antibod ies gave the positive immunological reaction with both, a soluble and plasm a membrane-bound nitrate reductase. Anti-NR antibody as well as IgG fragmen ts almost totally inhibited the nitrate reductase activity in cytosol provi ng a crossreaction of antibody with the catalytic site of a soluble NR. Ant i-NR IgG fragments, but not undigested polyclonal antibodies affected the a ctivity of the nitrate reductase associated with plasma membranes. Discrepa ncy in the action of intact antibodies and fragments obtained after they di gestion were interpreted as a consequence of same differences in the abilit y of those molecules to the penetration through the membrane. Undigested anti-NR antibody have no effect on the nitrate uptake by intact plants, as well as by the right-side plasma membrane vesicles. On the other hand, IgG fragments of polyclonal antibodies abolished almost totally the nitrate uptake in the case of intact seedlings, but have only slight effect on the NO3- uptake in plasma membranes. On the basis of above findings, so me relations between nitrate uptake and its assimilation inside the cell ar e suggested. Since IgG fragments only slightly changed the NO3- absorption in vesicles whereas the activity of plasmalemma associated nitrate reductas e was strongly repressed, we concluded that the PM-NR is not structurally i nvolved in the nitrate transport through the membrane.