Light dependent reduction of nitrate by pea chloroplasts in the presence of nitrate reductase and C4-dicarboxylic acids |
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Authors: | Colin M. House John W. Anderson |
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Affiliation: | Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia |
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Abstract: | In the presence of purified nitrate reductase (NR) and 1 mM NADH, illuminated pea chloroplasts catalysed reduction of NO3? to NH3 with the concomitant evolution of O2. The rates were slightly less than those for reduction of NO2? to NH3 and O2, evolution by chloroplasts in the absence of NR and NADH (ca 6 μg atoms N/mg Chl/hr). Illuminated chloroplasts quantitatively reduced 0.2 mM oxaloacetate (OAA) to malate. In the presence of an extrachloroplast malate-oxidizing system comprised of NAD-specific malate dehydrogenase (NAD-MDH), NAD, NR and NO3?, illuminated chloroplasts supported OAA-dependent reduction of NO3? to NH3 with the evolution of O2. The reaction did not proceed in the absence of any of these supplements or in the dark but malate could replace OAA. The results are consistent with the reduction of NO3?by reducing equivalents from H2O involving a malate/OAA shuttle. The ratios for O2, evolved: C4-acid supplied and N reduced: C4-acid supplied in certain experiments imply recycling of the C4-acids. |
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Keywords: | Leguminosae peas Gramineae wheat nitrate reduction nitrite reduction malate shuttle nitrate reductase NAD-specific-malate dehydrogenase NADP-specific-malate dehydrogenase light dependent chloroplasts. |
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