How does glutamine synthetase activity determine plant tolerance to ammonium? |
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Authors: | C Cruz A F M Bio M D Domínguez-Valdivia P M Aparicio-Tejo C Lamsfus M A Martins-Loução |
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Institution: | (1) Departamento de Biologia Vegetal, Faculdade de Ciências de Lisboa, Centro de Ecologia e Biologia Vegetal – CEBV, Campo Grande, Bloco C-2, Piso 4, 1749-016 Lisboa, Portugal;(2) Departamento de Ciencias del Medio Natural, Universidad Publica de Navarra, Pamplona, Navarra, Spain;(3) Grupo de Ambiente do CMRP, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal |
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Abstract: | The wide range of plant responses to ammonium nutrition can be used to study the way ammonium interferes with plant metabolism
and to assess some characteristics related with ammonium tolerance by plants. In this work we investigated the hypothesis
of plant tolerance to ammonium being related with the plants’ capacity to maintain high levels of inorganic nitrogen assimilation
in the roots. Plants of several species (Spinacia oleracea L., Lycopersicon esculentum L., Lactuca sativa L., Pisum sativum L. and Lupinus albus L.) were grown in the presence of distinct concentrations (0.5, 1.5, 3 and 6 mM) of nitrate and ammonium. The relative contributions
of the activity of the key enzymes glutamine synthetase (GS; under light and dark conditions) and glutamate dehydrogenase
(GDH) were determined. The main plant organs of nitrogen assimilation (root or shoot) to plant tolerance to ammonium were
assessed. The results show that only plants that are able to maintain high levels of GS activity in the dark (either in leaves
or in roots) and high root GDH activities accumulate equal amounts of biomass independently of the nitrogen source available
to the root medium and thus are ammonium tolerant. Plant species with high GS activities in the dark coincide with those displaying
a high capacity for nitrogen metabolism in the roots. Therefore, the main location of nitrogen metabolism (shoots or roots)
and the levels of GS activity in the dark are an important strategy for plant ammonium tolerance. The relative contribution
of each of these parameters to species tolerance to ammonium is assessed. The efficient sequestration of ammonium in roots,
presumably in the vacuoles, is considered as an additional mechanism contributing to plant tolerance to ammonium nutrition. |
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Keywords: | Ammonium tolerance Glutamate dehydrogenase Glutamine synthetase Lactuca Lupinus Lycopersicon Pisum Spinacia |
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