thiourea and 2-phenyl-4-4-5-5-tetramethylimidazoline-1-oxyl-3-oxide

Brassinosteroids (BRs) play pivotal roles in modulating plant growth, development, and stress responses. In this study, a

Topics: Acclimatization; Brassinosteroids; Cold-Shock Response; Cyclic N-Oxides; Free Radical Scavengers; Hydrogen Peroxide; Imidazoles; Medicago truncatula; Mitochondrial Proteins; Nitric Oxide; Oxidoreductases; Plant Proteins; Signal Transduction; Thiourea

Nitrification is a critical process for the balance of reduced and oxidized nitrogen pools in nature, linking mineralization to the nitrogen loss processes of denitrification and anammox. Recent studies indicate a significant contribution of ammonia-oxidizing archaea (AOA) to nitrification. However, quantification of the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to in situ ammonia oxidation remains challenging. We show here the production of nitric oxide (NO) by Nitrosopumilus maritimus SCM1. Activity of SCM1 was always associated with the release of NO with quasi-steady state concentrations between 0.05 and 0.08 μM. NO production and metabolic activity were inhibited by the nitrogen free radical scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Comparison of marine and terrestrial AOB strains with SCM1 and the recently isolated marine AOA strain HCA1 demonstrated a differential sensitivity of AOB and AOA to PTIO and allylthiourea (ATU). Similar to the investigated AOA strains, bulk water column nitrification at coastal and open ocean sites with sub-micromolar ammonia/ammonium concentrations was inhibited by PTIO and insensitive to ATU. These experiments support predictions from kinetic, molecular and biogeochemical studies, indicating that marine nitrification at low ammonia/ammonium concentrations is largely driven by archaea and suggest an important role of NO in the archaeal metabolism.

Topics: Ammonia; Ammonium Compounds; Aquatic Organisms; Archaea; Betaproteobacteria; Cyclic N-Oxides; Denitrification; Imidazoles; Nitric Oxide; Nitrification; Nitrogen; Oxidation-Reduction; Thiourea

A concentration-dependent toxicity of hydrogen peroxide (H(2)O(2)) was observed on growth yield, chlorophyll a content and chlorophyll fluorescence characteristics of the green microalga Scenedesmus obliquus under laboratory batch culture conditions. The addition of sodium nitroprusside, a nitric oxide (NO) donor, in combination with H(2)O(2) prevented chlorophyll losses, and the inhibition level of growth yield, maximum quantum yield of photosystem II (PSII) and the light-adapted quantum yield of PSII were significantly reduced. The antioxidant compounds, penicillamine and thiourea also reduced the damage caused by H(2)O(2) exposure. The protective actions of sodium nitroprusside were, however, arrested in cultures where sodium nitroprusside was supplemented in combination with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), a specific scavenger of NO. The NO(3)(-)-grown Scenedesmus depicted less sensitivity to H(2)O(2) toxicity with respect to the quantum yields of PSII as compared to its NH(4)(1)-grown counterpart. The role of NO in providing protection against H(2)O(2) toxicity to the processes under study was discussed.

Topics: Animals; Antioxidants; Chlorophyll; Chlorophyll A; Chlorophyta; Cyclic N-Oxides; Free Radical Scavengers; Hydrogen Peroxide; Imidazoles; Light-Harvesting Protein Complexes; Nitric Oxide; Nitric Oxide Donors; Nitroprusside; Penicillamine; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Thiourea