title: In vivo gas exchange measurement of the site and dynamics of nitrate reduction in soybean.
abstract: A gas analysis system was built to study the relationship between the reductant cost of NO(3)(-) assimilation and the measured rate of CO(2) and O(2) 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 CO(2) + measured rate of O(2)], in moles of high-energy electron [e(-)] per gram per hour) in plants in the presence (N+) and absence (N-) of NO(3)(-). The differences in DRUR between the N+ and N- treatments provided a measure of the NO(3)(-)-coupled DRUR of 25-d-old plants, whereas a (15)NO(3)(-)-enriched nutrient solution was used to obtain an independent measure of the rate of NO(3)(-) 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 NO(3)(-) 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 NO(3)(-) assimilation in plant tissue.
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Yan-Ping
authors.initials: YP
authors.lastname: Cen
authors.forename: David B
authors.initials: DB
authors.lastname: Layzell
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D003624:Darkness; D008027:Light; D008954:Models, Biological; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009587:Nitrogen Isotopes; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018547:Plant Stems / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018514:Plant Structures / Q000378:metabolism*; D013025:Glycine max / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D010100:Oxygen