Plant Physiol. Drug Metab Dispos
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Plant Physiology 76:59-64 (1984)
© 1984 American Society of Plant Biologists

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Articles

Effects of N2 Deficiency on Transport and Partitioning of C and N in a Nodulated Legume 1

John S. Pate, Craig A. Atkins, David B. Layzell2 and Barry J. Shelp3

Botany Department, University of Western Australia, Nedlands, WA 6009, Australia

Nodulated root systems of white lupin (Lupinus albus L. cv Ultra: Rhizobium strain WU425) were exposed to Ar:O2 (80:20, v/v) or Ar:N2:O2 (70:10:20, v/v/v) and C and N partitioning were examined over a 9- or 10-day period in comparison with control plants with nodulated roots retained in air. Accumulation of N ceased in plants exposed to Ar:O2 or was much reduced in plants exposed to Ar:N2:O2, but net C assimilation rates and profiles of C utilization remained similar to those of control N2-fixing plants. There was, however, a proportional reduction in CO2 evolution from nodulated roots of the Ar:O2 treatment. Xylem N levels fell rapidly after application of Ar:O2. C:N ratios of phloem sap of petioles and of stem base rose during the first day of Ar:O2 treatment and then fell progressively back to levels close to that of control plants as leaf reserves of N became available for loading of phloem. Stem top phloem sap increased progressively in C:N ratio throughout Ar:O2 treatment, presumably due to increasing shortage of xylem derived N for xylem to phloem exchange. Reexposure of Ar:O2-treated nodulated root systems to air prompted a rapid recovery of N2 fixation and restoration of plant N status. Rates of N2 fixation in plants whose roots were exposed to a range of N2 concentrations indicated an apparent Km of 10% N2 for the attached intact white lupin nodule.

2 Present address: Biology Department, Queen's University, Kingston, Ontario, Canada.

3 Present address: Department of Horticultural Science, University of Guelph, Guelph, Ontario N1G 2W1 Canada.

1 Supported by grants from the Australian Research Grants Scheme and the Wheat Industry Research Council of Australia.




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