Plant Physiol, March 2003, Vol. 131, pp. 1147-1156
In Vivo Gas Exchange Measurement of the Site and Dynamics of
Nitrate Reduction in Soybean1
Yan-Ping
Cen and
David B.
Layzell*
Department of Biology, Queen's University, Kingston, Ontario,
Canada K7L 3N6
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.
1
This work was supported by the Natural Sciences
and Engineering Research Council of Canada (grant to D.B.L.).
*
Corresponding author; e-mail Layzelld{at}biology.queensu.ca;
fax 613-533-6645.
© 2003 American Society of Plant Biologists
