The control of glutamine synthetase level in Lemna minor L.

Rhodes, David; Rendon, Gloria; Stewart, George R.

doi:10.1007/bf00385596

Cited by 188 publications

(78 citation statements)

References 27 publications

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“…A atividade da GS foi determinada de acordo com Rhodes et al (1975). Amostras de 0,5 g de massa fresca foram obtidas de fragmentos das três folhas mais novas das plantas, excetuando-se a folha mais interna.…”

Section: Methodsunclassified

Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho

Majerowicz¹,

Pereira²,

Médici³

et al. 2002

Rev. bras. Bot.

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-(Nitrogen use efficiency in local and improved maize varieties). The requirement of nitrogen fertilizers to increase crop productivity risks environmental contamination and increases farmer production costs up to 40% in maize cultivation. The objective of this study was to evaluate physiologic parameters related to nitrogen use efficiency and so contribute to maize breeding programs targeting grain yield in low-N environments. Three maize local varieties (Pedra Dourada, Catetão e Carioca), two improved varieties selected in fertily soil (BR 105 and BR 106) and two improved varieties selected under low N (Nitroflint and Nitrodente) were studied. Plants were supplied with Hoagland nutrient solution with two N levels in the form of nitrate (75%) and ammonium (25%). Low N plants were supplied with 1 mM of N and high N plants with 15 mM of N. The experiment, conducted in greenhouse, was carried out in complete randomized block design with three replicates and 14 factorial treatments. Nitrogen deficiency intensely decreased shoot growth and had a neglectful effect on root system. The biochemical traits studied (pigment contents, nitrate reductase and glutamine synthetase activities) were affected by N supply but did not show variability among genotypes. Dry matter accumulation in nitrogen deficient plants correlated positively (0.86) with the dry matter accumulation in the root system of maize genotypes. Our results suggest that the investigation of root properties may provide important precocious data about nitrogen use efficiency of maize genotypes.RESUMO -(Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho). O uso de fertilizantes, além dos riscos de contaminação ambiental, onera o agricultor, chegando a representar 40% dos custos de produção na cultura do milho. O presente estudo visa identificar características fisiológicas relacionadas com o aumento da eficiência do uso do nitrogênio e assim subsidiar programas de melhoramento genético direcionados para obtenção de genótipos de milho produtivos em solos com baixa disponibilidade de nitrogênio. Foram estudadas as variedades de milho Pedra Dourada, Catetão, Carioca (variedades locais, não melhoradas), BR 106, BR 105 (variedades melhoradas em solos férteis), Nitroflint e Nitrodente (variedades melhoradas em solos pobres em N). Plântulas de milho receberam solução nutritiva de Hoagland modificada quanto às fontes de N, sendo utilizadas duas doses de N (1 mM e 15 mM), 75% na forma nítrica e 25% na forma amoniacal. O experimento, composto por um fatorial 2 × 7 (duas doses de N e sete variedades) foi conduzido em casa de vegetação em blocos completos casualizados com três repetições. A deficiência de N afetou de modo muito mais intenso o crescimento das partes aéreas em todos os genótipos. As características bioquímicas estudadas (atividades da nitrato redutase, glutamina sintetase e conteúdo de pigmentos fotossintéticos) foram sensíveis à disponibilidade de N mas não permitiram discriminar diferenças genotípicas. A massa sec...

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Section: Methodsunclassified

Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho

Majerowicz¹,

Pereira²,

Médici³

et al. 2002

Rev. bras. Bot.

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“…There appear to be no reports of glutamine synthetase isoenzymes in algae, although the enzyme has been purified from a thermophilic strain of Chlorella pyrenoidosa and characterized in some detail (21 Enzyme Assays. The synthetase and transferase activities were determined as described by Guiz et al (7) and Rhodes et al (22), respectively. Protein was assayed by the method of Bradford (3).…”

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confidence: 99%

Occurrence of Isóenzymes of Glutamine Synthetase in the Alga Chlorella kessleri

Sumar

Casselton²,

McNally³

et al. 1984

Plant Physiol.

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Recent work has shown that glutamine synthetase (EC 6.3.1.2), the key enzyme of ammonia metabolism, occurs in multiple molecular forms in many higher plants (1, 7, 12, 15, 16, 18-20, 23, 27). Ion exchange chromatography and subcellular localization studies have shown the presence of two isoenzymes in photosynthetically active tissue: GS, is localized in the cytoplasm whereas GS2 is found in chloroplasts (10,11,17). These isoenzymes differ in several respects, including their pH optima, heat stability, and Km for glutamate (1,9,16,18,19 Extracts from cells of Chlorella grown under a range of nutritional conditions were found to exhibit two peaks of glutamine synthetase activity when subjected to ion exchange chromatography (Fig. 1). The first peak eluted at 70 mm KCI and the second at 230 mm KCI, and by analogy with the corresponding chromatographic forms in higher plants they are designated GS, and GS2 (see Refs. 9 and 16). GS, was always the major form present, comprising 60 to 80% of the total activity. It is evident from the results in Figure 1 and those summarized in Table I

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“…To prevent a penetration of external L-MSO into the permeabilized cells, cells were washed on the filter with 10 ml distilled H20 prior to permeabilization. Synthetase activity was determined as described by Rhodes et al (14).…”

Section: Methodsmentioning

confidence: 99%

Ammonia Exchange and Photorespiration in Chlamydomonas

Peltier

Thibault²

1983

Plant Physiol.

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Two hours after the addition of L-methionine-DL-sulfoxmie to the cell suspension, glutamine synthetase activity was inhibited by more than 90% in air-grown Chiamydomonas reshardii Cells continued to take up NH3 from the medium provided that the concentration of dissolved CO2 was high (equilbrated with 4% CO2 in air). This NH3 uptake, about 30% of the control, is discussed in terms of glutamate dehydrogenase activity. Without C02, or with a low CO2 level, a NH3 excretion was observed, the rate of which depended on the actual concentradon of the dissolved CO2. Experiments with 15NH3 demonstrated that no NH3 uptake was masked by this excretion and inversely that no excretion occurred during the uptake in the conditions where it took place. Furthermore, the NH3 excretion observed in the absence of CO2 increased when 02 concentration rose to 15% and was inhibited when 10 milimolar isonicotinic acid hydrazide was supplied to the algal suspension. Thus, NH3 excretion in the presence of L-methionine-DL-sulfoxlmine seems to be related to a photorespiratory process inasmuch as it presents the same properties with regard to the 02 and the isonicotinic acid hydrazide effects. These results favor the hypothesis that NH3 produced in the medium originates from the glycine to serine reaction. On the other hand, partial inhibition (50%) of photosynthesis by L-methionine-DL-sulfoximine was attributed to uncoupling between electron transfer and photophosphorylation due to NH3 accumulation into the cell.L-MSO' is known to be an irreversible inhibitor of GS (16) without effect on GDH (2, 13). Because of these properties, the use of this compound allowed a distinction between the two pathways capable of NH3 assimilation (9). Thus, using L-MSO, Stewart and Rhodes on Lemna minor (20) and Cullimore and Sims on Chlamydomonas (5) concluded that NH3 assimilation occurred exclusively via the GS-glutamate synthase pathway; GDH would be devoid of any anabolic role.Furthermore, when a green plant is treated with L-MSO in the presence of air, NH3 production takes place: this phenomenon has been observed both in higher plants like tobacco (18) or spinach (11) and in the green alga Chlamydomonas (4). This NH3 production was shown to be light-dependent, abolished by DCMU, and absent when algae were bubbled with air supplemented with 3% C02 (4). From this, it was concluded that NH3 originated from photorespiration. This conclusion agrees with the results of Keys et al. (8) (2.2%), although in such conditions photorespiration is known to be largely decreased (3). In addition, they showed that L-MSO induced a rapid and complete inhibition of photosynthesis.In this paper, we study the effect of CO2 concentration on NH3 exchange and photosynthesis in air-grown Chlamydomonas treated with L-MSO. Furthermore, we report on the effects of 02 concentration and INH, an inhibitor of photorespiration, on NH3 excretion which occurs in the presence of L-MSO. We discuss our results in relation to the NH3-assimilating pathway and photorespiratory NH3-recyc...

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The control of glutamine synthetase level in Lemna minor L.

Cited by 188 publications

References 27 publications

Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho

Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho

Occurrence of Isóenzymes of Glutamine Synthetase in the Alga Chlorella kessleri

Ammonia Exchange and Photorespiration in Chlamydomonas

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