Regulation of nitrate and nitrite reduction in barley leaves

Reduction of nitrate and accumulation of nitrite were studied in barley (Hordeum vulgare L. cv. Gars Clipper ex Napier) leaf sections in the dark and in the light, under aerobic (air and mixtures of O₂ and N₂) or anaerobic (N₂) conditions. Oxygen prevented nitrite accumulation but had no effect on accumulated or infiltrated nitrite. Most of the nitrite accumulated under dark-anaerobic conditions was in the "cytoplasmic" (the cell section between the plasma lemma and the tonoplast) fraction of the tissue. Reduction of nitrate was stimulated by 2, 4-dinitrophenol in tissue under dark-air and by 3-(3', 4'-dichlorophenyl)-l, l-dimethyl urea (DCMU) and carbonyl cyanide m -chlorophenylhydrazone (CCCP) in tissue under all environmental conditions studied. Nitrite accumulated in the light in DCMU-treated tissue under N₂ or under aerobic conditions in the presence of CCCP. On its own, CCCP did not promote accumulation of nitrite in leaf sections under light-air. A model for the reduction of nitrate and nitrite is proposed.