The Release of Nitrite from Barley Roots in Response to Metabolic Inhibitors, Uncoupling Agents, and Anoxia

Abstract

When excised sterile barley roots, from plants which had been grown in the presence of nitrate, were placed under low oxygen tensions, nitrite was released into the external solution. The maximum leakage of nitrite occurred under completely anaerobic conditions. Nitrite was also released from barley roots under aerobic conditions when uncouplers of oxidative phosphorylation (DNP, CCCP1, pentachlorophenol) or certain simple organic acids were supplied. Inhibitors of the Krebs cycle, or of respiratory electron transport, were much less effective in causing the loss of nitrite, possibly because these compounds did not in general inhibit root respiration severely. Nitrite release, in response to any of the above treatments, was accompanied by an accumulation of nitrite within the tissue. It was concluded that an increase in membrane permeability, and a decrease in ATP synthesis, were contributory causes of this phenomenon, although neither could explain the experimental observations completely. There was however no evidence that the pentose phosphate pathway, which is regarded as the source of reducing power for nitrite reduction, was inhibited under conditions which favoured nitrite release.