| Abstrakt: |
Abstract: a1_The effect of some ammonium salts on nitrate reductase (NR) level, onin vivo nitrate reduction and on nitrate content was followed in the presence of nitrate in the medium, under changing experimental conditions, in excised Pisum sativum roots, and their effect was compared with that of KNO3, Ca(NO3)2 and NaNO3 at 15 mM NO3- concentration, i.e. at a concentration which considerably exceeded the level of saturation with nitrate with respect to nitrate reductase. The effect of ammonium salts on NR level is indirect and changes from a positive one to a strongly negative one which is dependent on the time of action of the salt, on the presence of other cations, on pH of the solution of the ammonium salt and on the nature of the anion of the ammonium salt. A positive effect on the enzyme level can be observed in the presence of other cations than NH4+ at suitable concentrations of those ammonium salts, the solutions of which have their pH values in the acid region (i.e. NH4H2PO4, (NH4)2SO4 and NH4NO3). However their positive effect is independent of the presence of NH4+ ions, and it is obviously the result of an increased concentration of H+ ions. A clear-cut negative effect on NR level can be observed after 24 h in one-salt NH4NO3 solution where NH4+ is not balanced with other cations and thus certainly can adversely influence many metabolic processes, and in the solutions containing neutral (pH 6.2) and dibasic ammonium phosphates in which dissolved undissociated ammonia [(NH3). (H2O) which can also affect many metabolic processes incl. proteosynthesis] probably has a toxic influence. The in vivo nitrate reduction is always depressed in excised pea roots in the presence of ammonium salts in the medium, regardless of the level of nitrate reductase. |
