Lack of end-product control of nitrite reductase level in pea roots

Abstract

The effects of various ammonium salts and amino acids on nitrite reductase (NIR) induction in isolated pea roots cultured in media containing nitrate or nitrite and either exogenous sucrose or no sugar were investigated. Thg aim of these investigations was to determine if the NIR level is subject to end-product control. The results showed that even though some ammonium salts and casamino acids can depress NIR level under certain conditions this inhibition cannot be interpreted in terms of direct end-product inhibition of NIR synthesis because their effects were dependent on the character (anion) and toxicity of the respective ammonium salt, on the presence of exogenous sucrose in the induction medium, and on the inducer of NIR. NH4HCO3 inhibited NIR induction at those concentrations which were toxic to the roots, ammonium phosphates hampered NIR induction only in roots exposed to nitrite in media containing sucrose, while casamino acids slightly depressed NIR induction only in roots exposed to nitrate and exogenous sucrose. The results further show that the basal (noninduced) NIR level changes little even under strongly toxic conditions.