title: Involvement of nitrite in the nitrate-mediated modulation of fermentative metabolism and nitric oxide production of soybean roots during hypoxia.
abstract: It is widely accepted that nitrate but not ammonium improves tolerance of plants to hypoxic stress, although the mechanisms related to this beneficial effect are not well understood. Recently, nitrite derived from nitrate reduction has emerged as the major substrate for the synthesis of nitric oxide (NO), an important signaling molecule in plants. Here, we analyzed the effect of different nitrogen sources (nitrate, nitrite and ammonium) on the metabolic response and NO production of soybean roots under hypoxia. Organic acid analysis showed that root segments isolated from nitrate-cultivated plants presented a lower accumulation of lactate and succinate in response to oxygen deficiency in relation to those from ammonium-cultivated plants. The more pronounced lactate accumulation by root segments of ammonium-grown plants was followed by a higher ethanol release in the medium, evidencing a more intense fermentation under oxygen deficiency than those from nitrate-grown plants. As expected, root segments from nitrate-cultivated plants produced higher amounts of nitrite and NO during hypoxia compared to ammonium cultivation. Exogenous nitrite supplied during hypoxia reduced both ethanol and lactate production and stimulated cyanide-sensitive NO emission by root segments from ammonium-cultivated plants, independent of nitrate. On the other hand, treatments with a NO donor or a NO scavenger did not affect the intensity of fermentation of soybean roots. Overall, these results indicate that nitrite participates in the nitrate-mediated modulation of the fermentative metabolism of soybean roots during oxygen deficiency. The involvement of mitochondrial reduction of nitrite to NO in this mechanism is discussed.
authors.affiliation: Department of Plant Biology, Institute of Biology, University of Campinas-UNICAMP, CP 6109 Campinas, SP 13083-970, Brazil. halleyco@unicamp.br
authors.forename: Halley C
authors.initials: HC
authors.lastname: Oliveira
authors.forename: Ione
authors.initials: I
authors.lastname: Salgado
authors.forename: Ladaslav
authors.initials: L
authors.lastname: Sodek
mesh_terms: D001565:Benzoates / Q000494:pharmacology; D002264:Carboxylic Acids / Q000378:metabolism; D005285:Fermentation / Q000187:drug effects; D008401:Gas Chromatography-Mass Spectrometry; D007093:Imidazoles / Q000494:pharmacology; D007773:Lactates / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009573:Nitrites / Q000378:metabolism* / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000494:pharmacology; D013025:Glycine max / Q000187:drug effects / Q000378:metabolism*; D013386:Succinates / Q000378:metabolism; D013997:Time Factors; D014226:Triazenes / Q000494:pharmacology
chemical_list: C114535:1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene; D001565:Benzoates; D002264:Carboxylic Acids; D007093:Imidazoles; D007773:Lactates; D009566:Nitrates; D020030:Nitric Oxide Donors; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D013386:Succinates; D014226:Triazenes; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009569:Nitric Oxide; D010100:Oxygen