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Published on February 27, 2003; 10.1104/pp.102.019430

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Received December 18, 2002
Returned for revision December 24, 2002
Accepted December 24, 2002

In Vivo Gas Exchange Measurement of the Site and Dynamics of Nitrate Reduction in Soybean

Yan-Ping Cen and David B. Layzell *

Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6

* Corresponding author; email: Layzelld{at}biology.queensu.ca.

A gas analysis system was built to study the relationship between the reductant cost of NO3- assimilation and the measured rate of CO2 and O2 exchange in roots, leaves, and stems+ petioles of soybean (Glycine max L. Merr. cv Maple glen) plants. The measurements were used to calculate the diverted reductant utilization rate (DRUR = 4*[measured rate of CO2 + measured rate of O2], in moles of high-energy electron [e-] per gram per hour) in plants in the presence (N+) and absence (N-) of NO3-. The differences in DRUR between the N+ and N- treatments provided a measure of the NO3--coupled DRUR of 25-d-old plants, whereas a 15NO3--enriched nutrient solution was used to obtain an independent measure of the rate of NO3- assimilation. The measured reductant cost for the whole plant was 9.6 e- per N assimilated, a value within the theoretical range of four to 10 e- per N assimilated. The results predicted that shoots accounted for about 55% of the whole-plant NO3- assimilation over the entire day, with shoots dominating in the light, and roots in the dark. The gas analysis approach described here holds promise as a powerful, noninvasive tool to study the regulation of NO3- assimilation in plant tissue.






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