Implicaciones de la nutrición amoniacal en el metabolismo y emisiones de gases nitrogenados en trigo y tomate

Resumen

Ammonium nutrition can induce deleterious effects in plants. In this workthe metabolic mechanisms involved in the tolerance to this kind of nutrition havebeen studied by means of applying increasing concentrations of ammonium to thetolerant tomato (Solanum lycopersicum Mill.) variety Agora Hybrid F1 and by meansof applying different levels of irradiance in wheat (Triticum aestivum L. var.Cezanne). The effect of ammonium nutrition has also been studied on thephotosynthetic gaseous exchange parameters as well as on the exchange of otherenvironmentally harmful gases like nitric oxide (NO), nitrogen dioxide (NO2),nitrous oxide (N2O), ammonia (NH3) and methane (CH4).The main tolerance mechanism performed by both species is theenhancement of an efficient assimilation of ammonium in the roots. With this aim, agood coordination is necessary in the last term between the export ofphotosynthates to the roots together with the subsequent provision of carbonskeletons from the tricarboxylic acid cycle (TCA), mainly in the form of ¿-ketoglutarate, and the activity of the enzymes involved in ammonium assimilation.Among these enzymes, glutamate dehydrogenase (GDH) and asparagine synthetase(AS) show to play an important role in the roots in order to compensate for thepossible lack of activity of the glutamine synthetase pathway (GS/GOGAT) underconditions of ammonium nutrition.Both species behave as NO2 sinks, and when they are grown underammonium nutrition they show a potential to emit NO, NH3, N2O and CH4 which isquenched due to the lower level of stomatal aperture induced by this kind ofnutrition. The important role of the plants in mitigating global warming as aconsequence of their photosynthetic assimilation of CO2 is reduced underammonium nutrition in both species due to the emission of the greenhouse gasesN2O and CH4 from the leaves. An increase of irradiance enhances the CO2assimilation rate, thus mitigating in a greater manner this loss of environmentalefficiency in such a way that ammonium nutrition can result viable both from theenvironmental and the productive points of view in the plants tolerant toammonium in terms of biomass and/or protein accumulation.Amonioan oinarritutako elikadurak ondorio kaltegarriak izan ditzakelandareengan. Lan honetan, elikadura mota horrenganako jasankortasunean partehartzen duten mekanismo metabolikoak ikertu dira; batetik, Agora Hybrid F1tomate (Solanum lycopersicum Mill.) barietate jasanberari gero eta amoniokontzentrazio handiagoak ezarriz, eta bestetik, Cezanne barietateko gariari (Triticumaestivum L.) irradiatze maila ezberdinak ezarriz.Era berean, amonio elikadurak fotosintesiko gas trukeko parametroetanduen eragina neurtu da, ingurugirorako kaltegarriak diren bestelako gasenigorpenarekin batera, hala nola, oxido nitrikoa (NO), nitrogeno dioxidoa (NO2),oxido nitrosoa (N2O), amoniakoa (NH3) edota landaretzatik igorritako metanoa(CH4).Tomateak zein gariak, sustraietan ematen den amonioaren asimilazioareneraginkortasunaren sustatzea dute jasankortasunerako mekanismo nagusi.Horretarako, sustrairako fotosintatoen esportazioaren eta azido trikarboxilikoenziklotik datozen karbono-eskeletoen, ¿-zetoglutaratoa nagusiki, hornidurarenarteko koordinazio egokia behar da, amonioaren asimilazioan inplikaturik daudenentzimen aktibitatearekin batera. Izan ere, entzima hauek, glutamatodeshidrogenasak (GDH) eta asparragina sintetasak (AS), eginkizun garrantzitxuabetetzen dute amonio elikadura baldintzetan sustraiean eman daitekeen glutaminasintetasa (GS/GOGAT) bidearen akibitate falta orekatzerako orduan.Bi espezieek NO2-aren isurbide gisa jokatzen dute, eta amonio elikadurapeanhazten direnean, agertzen duten irekidura estomatikoaren maila baxua dela eta NO,NH3, N2O eta CH4 -aren igorpen potentzialak indargeturik agertzen dira.Orokorrean, landareek berotegi-efektuaren murrizketan parte hartzen dute CO2-aren asimilazio fotosintetikoari esker. Baina, amonio elikaduraren kasuan, tomateakzein gariak erakusten duten efektu onuragarri hori gutxiturik azaltzen dahostoetatik emanten den N2O eta CH4 berotegi-gasen igorpenaren ondorioz. Halaere, irradiantziaren emendatzeak CO2-aren finkatze tasa handiagotzen du, berotegiefektuarenmurrizketa areagotuz.Hortaz, biomasa eta proteína metaketari dagokionez jasanberak direnlandareetan, amonio nutrizioa bideragarria liteke ingurugiroaren osasunaren zeinproduktibitatearen ikuspuntutik.