RESUMEN

BACKGROUND: Microalgae CO2 fixation results in the production of biomass rich in high-valuable products, such as fatty acids and carotenoids. Enhanced productivity of valuable compounds can be achieved through the microalgae's ability to capture CO2 efficiently from sources of high CO2 contents, but it depends on the species. Culture collections of microalgae offer a wide variety of defined strains. However, an inadequate understanding of which groups of microalgae and from which habitats they originate offer high productivity under increased CO2 concentrations hampers exploiting microalgae as a sustainable source in the bioeconomy. RESULTS: A large variety of 81 defined algal strains, including new green algal isolates from various terrestrial environments, were studied for their growth under atmospheres with CO2 levels of 5-25% in air. They were from a pool of 200 strains that had been pre-selected for phylogenetic diversity and high productivity under ambient CO2. Green algae from terrestrial environments exhibited enhanced growth up to 25% CO2. In contrast, in unicellular red algae and stramenopile algae, which originated through the endosymbiotic uptake of a red algal cell, growth at CO2 concentrations above 5% was suppressed. While terrestrial stramenopile algae generally tolerated such CO2 concentrations, their counterparts from marine phytoplankton did not. The tests of four new strains in liquid culture revealed enhanced biomass and chlorophyll production under elevated CO2 levels. The 15% CO2 aeration increased their total carotenoid and fatty acid contents, which were further stimulated when combined with the starvation of macronutrients, i.e., less with phosphate and more with nitrogen-depleted culture media. CONCLUSION: Green algae originating from terrestrial environments, Chlorophyceae and Trebouxiophyceae, exhibit enhanced productivity of carotenoids and fatty acids under elevated CO2 concentrations. This ability supports the economic and sustainable production of valuable compounds from these microalgae using inexpensive sources of high CO2 concentrations, such as industrial exhaust fumes.

Asunto(s)

Chlorophyta , Microalgas , Dióxido de Carbono , Filogenia , Biomasa , Ácidos Grasos , Nutrientes , Agua Dulce

RESUMEN

There are many reports of an arginine-dependent nitric oxide synthase activity in plants; however, the gene(s) or protein(s) responsible for this activity have yet to be convincingly identified. To measure nitric oxide synthase activity, many studies have relied on a citrulline-based assay that measures the formation of L-citrulline from L-arginine using ion exchange chromatography. In this article, we report that when such assays are used with protein extracts from Arabidopsis, an arginine-dependent activity was observed, but it produced a product other than citrulline. TLC analysis identified the product as argininosuccinate. The reaction was stimulated by fumarate (> 500 microM), implicating the urea cycle enzyme argininosuccinate lyase (EC 4.3.2.1), which reversibly converts arginine and fumarate to argininosuccinate. These results indicate that caution is needed when using standard citrulline-based assays to measure nitric oxide synthase activity in plant extracts, and highlight the importance of verifying the identity of the product as citrulline.

Asunto(s)

Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Argininosuccinatoliasa/metabolismo , Citrulina/metabolismo , Óxido Nítrico Sintasa/metabolismo , Arabidopsis/enzimología , Arginina/metabolismo , Ácido Argininosuccínico/metabolismo , Bioensayo/métodos , Catálisis/efectos de los fármacos , Cromatografía por Intercambio Iónico , Cromatografía en Capa Delgada , Fumaratos/metabolismo , Fumaratos/farmacología , Cinética , Extractos Vegetales/metabolismo

RESUMEN

Wild type (WT), and nitrate reductase (NR)- and nitrite-reductase (NiR)-deficient cells of Chlorella sorokiniana were used to characterize nitric oxide (NO) emission. The NO emission from nitrate-grown WT cells was very low in air, increased slightly after addition of nitrite (200 microM), but strongly under anoxia. Importantly, even completely NR-free mutants, as well as cells grown on tungstate, emitted NO when fed with nitrite under anoxia. Therefore, this NO production from nitrite was independent of NR and other molybdenum cofactor enzymes. Cyanide and inhibitors of mitochondrial complex III, myxothiazol or antimycin A, but not salicylhydroxamic acid (inhibitor of alternative oxidase) inhibited NO production by NR-free cells. In contrast, NiR-deficient cells growing on nitrate accumulated nitrite and emitted NO at very high equal rates in air and anoxia. This NO emission was 50% inhibited by salicylhydroxamic acid, indicating that in these cells the alternative oxidase pathway had been induced and reduced nitrite to NO.

Asunto(s)

Chlorella/metabolismo , Complejo III de Transporte de Electrones/efectos de los fármacos , Mitocondrias/metabolismo , Óxido Nítrico/metabolismo , Antimicina A/farmacología , Hipoxia de la Célula , Chlorella/genética , Chlorella/crecimiento & desarrollo , Cianuros/farmacología , Complejo III de Transporte de Electrones/metabolismo , Inhibidores Enzimáticos/farmacología , Cinética , Metacrilatos , Mutación , Óxido Nítrico/análisis , Nitritos/metabolismo , Salicilamidas/farmacología , Tiazoles/farmacología , Compuestos de Tungsteno/metabolismo

RESUMEN

A nitrate reductase (NR)-null mutant of Arabidopsis was constructed that had a deletion of the major NR gene NIA2 and an insertion in the NIA1 NR gene. This mutant had no detectable NR activity and could not use nitrate as the sole nitrogen source. Starch mobilization was not induced by nitrate in this mutant but was induced by ammonium, indicating that nitrate was not the signal for this process. Microarray analysis of gene expression revealed that 595 genes responded to nitrate (5 mm nitrate for 2 h) in both wild-type and mutant plants. This group of genes was overrepresented most significantly in the functional categories of energy, metabolism, and glycolysis and gluconeogenesis. Because the nitrate response of these genes was NR independent, nitrate and not a downstream metabolite served as the signal. The microarray analysis also revealed that shoots can be as responsive to nitrate as roots, yet there was substantial organ specificity to the nitrate response.

Asunto(s)

Arabidopsis/enzimología , Arabidopsis/genética , Nitrato Reductasas/genética , Nitratos/farmacología , Arabidopsis/efectos de los fármacos , Arabidopsis/metabolismo , Secuencia de Bases , ADN de Plantas/genética , Perfilación de la Expresión Génica , Genoma de Planta , Mutación , Nitrato-Reductasa , Nitrato Reductasas/metabolismo , Nitratos/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos

RESUMEN

The nitrate transporter from Chlorella sorokiniana (accession number AY026523) has been cloned by screening a cDNA library based on mRNA isolated after 30 min treatment of Chlorella with 5 mM nitrate and with a RT-PCR product (730 bp) as a probe. The Chlorella sequence has similarity to known nitrate transporters of the NRT2 family (high-affinity nitrate transporters). The cDNA clone was used for functional expression in Xenopus oocytes and a nitrate-dependent current was measured at pH 5.5 but not at pH 7.4. A second algal gene or a second gene product was not needed for functional expression in Xenopus. Inhibitor studies in Chlorella indicated that protein phosphorylation/dephosphorylation is involved in nitrate induction of ChNRT2.1. In addition to nitrate, ChNRT2.1 expression is induced by nitroprusside, a NO donor, and is affected by glucose.

Asunto(s)

Proteínas de Transporte de Anión/genética , Chlorella/genética , Secuencia de Aminoácidos , Animales , Proteínas de Transporte de Anión/metabolismo , Chlorella/efectos de los fármacos , Clonación Molecular , Cicloheximida/farmacología , ADN Complementario/química , ADN Complementario/genética , Femenino , Regulación de la Expresión Génica/efectos de los fármacos , Potenciales de la Membrana/efectos de los fármacos , Datos de Secuencia Molecular , Transportadores de Nitrato , Nitratos/farmacología , Donantes de Óxido Nítrico/farmacología , Nitroprusiato/farmacología , Oocitos/efectos de los fármacos , Oocitos/fisiología , Fosforilación/efectos de los fármacos , Filogenia , Inhibidores de la Síntesis de la Proteína/farmacología , Compuestos de Amonio Cuaternario/farmacología , ARN Mensajero/efectos de los fármacos , ARN Mensajero/genética , ARN Mensajero/metabolismo , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Xenopus

RESUMEN

This investigation shows diurnal variations in the xylem sap composition of poplar (Populus tremula x P. alba). All major macronutrients reached a maximum concentration in the first half of the light period and decreased to the middle of the night. The relative abundance of the nutrients did not change during the day. The sap flow, which responded very fast to the environmental changes (2.2-fold increase within 10-20 min of illumination), reached a maximum value in the second half of the light period. Transpiration (and photosynthesis) was constant throughout the light phase. The calculated translocation rates displayed a maximum in the first half of the light period and therefore did not fit the time course of sap flow. During the night, translocation rates were 63-69% lower than the maximum. The regulation of nutrient translocation is discussed taking the active xylem loading into account. The axial distribution located the nitrate assimilation in younger leaves and storage of nitrate (and other macronutrients) in older leaves. Nitrate and potassium concentrations in the xylem sap did not change along the plant axis. However, the sap flow was greater in younger shoot sections than in older sections. We assume that the greater demand for nitrate in the younger shoot section was satisfied via an increased volume flow rather an increased nitrate concentration.

Asunto(s)

Nitratos/metabolismo , Brotes de la Planta/fisiología , Populus/fisiología , Potasio/metabolismo , Transporte Biológico/fisiología , Transporte Biológico/efectos de la radiación , Calcio/metabolismo , Cloruros/metabolismo , Ritmo Circadiano/fisiología , Luz , Magnesio/metabolismo , Nitrato-Reductasa , Nitrato Reductasas/metabolismo , Fotosíntesis/fisiología , Fotosíntesis/efectos de la radiación , Brotes de la Planta/efectos de la radiación , Transpiración de Plantas/fisiología , Transpiración de Plantas/efectos de la radiación , Populus/efectos de la radiación , Compuestos de Amonio Cuaternario/metabolismo , Sodio/metabolismo , Sulfatos/metabolismo

RESUMEN

Aldehyde oxidase (AO; EC 1.2.3.1) isoforms in roots of barley plants grown on ammonium or nitrate as nitrogen sources were studied. Roots of ammonium-grown barley plants exhibited considerable levels of AO2, AO3, and AO4 activities after native PAGE. Significantly lower AO2 and AO3 activity bands were observed in roots of plants grown on nitrate. When abscisic aldehyde was used as a substrate a strong response of the AO2 band was observed as well as a faint reaction of the AO3 band, but no activity of AO4 was observed using this substrate. The 160 and 145 kDa polypeptides were detected in ammonium grown plants. Root extracts of nitrate-fed plants revealed only a minor 145 kDa protein band and none of the 160 kDa subunit was detected. The assembly of the AO3 heterodimer requires the simultaneous presence of 160 and 145 kDa subunits. Subunit analysis of AO2 and AO4 revealed homodimeric composition of 160 and 145 kDa, respectively. Western blot analysis revealed changing AO subunits levels during germination and plant development. Differential expression of AO subunits (160 and 145 kDa) and subsequent formation of isoforms, which differ in substrate specificity, distribution and fulfil different enzymatic reactions, may constitute an important regulatory mechanism in the plant.

RESUMEN

The effect of short-term low temperature treatment on nitrate reductase (NR, EC 1.6.6.1) activity, NR protein and NR transcript levels in excised leaves of winter wheat (Triticum aestivum L. cv. Sadovo-1) was investigated. NR activity, measured in the presence of Mg2+ (NRact), doubled within 2 h at 4 degrees C, whereas NR activity, measured in the presence of EDTA (NRmax), did not respond to the cold treatment. Such an activation of NR occurred only if leaves were exposed to low temperature in the light but not in the dark. It was not affected by feeding cytoplasmic protein synthesis inhibitor, cycloheximide, or protein kinase inhibitor, staurosporin, but was completely prevented by okadaic acid, an inhibitor of protein phosphatases of the type 1 and 2 A. This inhibitory effect decreased gradually when okadaic acid-concentration in the nutrient solution was lowered below 1 &mgr;M and tended to disappear when leaves were fed with 10 nM okadaic acid. It was demonstrated that the cold-induced NR activation was dependent neither on cold-triggered calcium influx nor on high endogenous abscisic acid levels. The increased NRact in cold-exposed leaves was found to correlate with a higher level of NR transcript but not with an increased NR protein level. Feeding okadaic acid to these leaves prevented the cold-induced accumulation of NR mRNA. These data point to protein phosphatases of the type 2 A being involved in NR protein dephosphorylation and NR transcript accumulation as targets of activation by low temperature treatment.

Asunto(s)

Ciencia , Métodos , Homeopatía