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Evidence for an operative glutamine translocator in chloroplasts from maritime pine ( Pinus pinaster Ait.) cotyledons
Author(s) -
Claros M. G.,
Aguilar M. L.,
Cánovas F. M.
Publication year - 2010
Publication title -
plant biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 1435-8603
DOI - 10.1111/j.1438-8677.2009.00274.x
Subject(s) - glutamate synthase , biology , glutamine , glutamine synthetase , chloroplast , biochemistry , ammonium , nitrogen assimilation , photorespiration , cytosol , glutamate receptor , phloem , marchantia polymorpha , botany , amino acid , photosynthesis , enzyme , chemistry , receptor , organic chemistry , gene
In higher plants, ammonium is assimilated into amino acids through the glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle. This metabolic cycle is distributed in different cellular compartments in conifer seedlings: glutamine synthesis occurs in the cytosol and glutamate synthesis within the chloroplast. A method for preparing intact chloroplasts of pine cotyledons is presented with the aim of identifying a glutamine–glutamate translocator. Glutamine–glutamate exchange has been studied using the double silicone layer system, suggesting the existence of a translocator that imports glutamine into the chloroplast and exports glutamate to the cytoplasm. The translocator identified is specific for glutamine and glutamate, and the kinetic constants for both substrates indicate that it is unsaturated at intracellular concentrations. Thus, the experimental evidence obtained supports the model of the GS/GOGAT cycle in developing pine seedlings that accounts for the stoichiometric balance of metabolites. As a result, the efficient assimilation of free ammonia produced by photorespiration, nitrate reduction, storage protein mobilisation, phenylpropanoid pathway or S ‐adenosylmethionine synthesis is guaranteed.