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Glutamate synthase activities and protein changes in relation to nitrogen nutrition in barley: the dependence on different plastidic glucose-6P dehydrogenase isoforms

Sergio Esposito, Gea Guerriero, Vincenza Vona, Vittoria Di Martino Rigano, Simona Carfagna and Carmelo Rigano
Journal of Experimental Botany
Vol. 56, No. 409 (January 2005), pp. 55-64
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/24030887
Page Count: 10
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Glutamate synthase activities and protein changes in relation to nitrogen nutrition in barley: the dependence on different plastidic glucose-6P dehydrogenase isoforms
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Abstract

In barley (Hordeum vulgare L. var. Nure), glutamate synthesis and the production of reducing power by the oxidative pentose phosphate pathway (OPPP) are strictly correlated biochemical processes. NADH-GOGAT was the major root isoform, whose activity increased on a medium supplied with $\mathrm{N}{\mathrm{H}}_{4}^{+}$ or $\mathrm{N}{\mathrm{O}}_{3}^{-}$; by contrast, no noticeable variations could be observed in the leaves of plants supplied with nitrogen. In the leaves, the major isoform is Fd-GOGAT, whose activity increased under nitrogen feeding. G6PDH activity increased in the roots supplied with nitrogen; no variations were observed in the leaves. Moreover, an increase of the P2 isoform in the roots was measured, giving 13.6% G6PDH activity localized in the plastids under ammonium, and 25.2% under nitrate feeding conditions. Western blots confirmed that P2-G6PDH protein was induced in the roots by nitrogen. P1-G6PDH protein was absent in the roots and increased in the leaves by nitrogen supply to the plants. The changes measured in cytosolic G6PDH seem correlated to more general cell growth processes, and do not appear to be directly involved in glutamate synthesis. The effects of light on Fd-GOGAT is discussed, together with the possibility for P2-G6PDH to sustain nitrogen assimilation upon illumination.

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