Carbon Dioxide Fixation by Lupin Root Nodules: I. Characterization, Association with Phosphoenolpyruvate Carboxylase, and Correlation with Nitrogen Fixation during Nodule Development

AUTOR(ES)

Christeller, John T.

RESUMO

In vivo CO2 fixation and in vitro phosphoenolpyruvate (PEP) carboxylase levels have been measured in lupin (Lupinus angustifolius L.) root nodules of various ages. Both activities were greater in nodule tissue than in either primary or secondary root tissue, and increased about 3-fold with the onset of N2 fixation. PEP carboxylase activity was predominantly located in the bacteroid-containing zone of mature nodules, but purified bacteroids contained no activity. Partially purified PEP carboxylases from nodules, roots, and leaves were identical in a number of kinetic parameters. Both in vivo CO2 fixation activity and in vitro PEP carboxylase activity were significantly correlated with nodule acetylene reduction activity during nodule development. The maximum rate of in vivo CO2 fixation in mature nodules was 7.9 nmol hour−1 mg fresh weight−1, similar to rates of N2 fixation and reported values for amino acid translocation.

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