Abstract
The effect of nitrate uptake, or its absence, on the utilization of nitrate previously accumulated by dark-grown, decpitated maize (Zea mays L., cv. DeKalb XL-45) seedlings was examined. Five-d-old plants that had been pretreated with 50 mM 14NO −3 for 20 h were exposed for 8 h to nutrient solutions containing either no nitrate or 50 mM 15NO −3 , 98.7 atom % 15N. The ambient solution, xylem exudate, and plant tissue were analyzed to determine the quantities of previously-accumulated (endogenous) 14NO −3 that were translocated to the xylem, lost to the solution, or reduced within the tissue during the 8-h period. Energy was continuously available to the roots from the attached endosperm. In the absence of incoming nitrate, appreciable reduction and translocation of the endogenous 14NO −3 occurred, but efflux of 14NO −3 to the external solution was minimal. In contrast, during 15NO −3 uptake, there was considerable efflux of 14NO −3 as well as translocation of 14NO −3 to the xylem, but little 14NO −3 was reduced. Thus there appeared to be an inverse relationship between 14NO −3 efflux and reduction. The data are tentatively interpreted on the basis of a model which envisages (a) two storage locations within roots, one of which primarily supplies nitrate for translocation and the other of which primarily supplies nitrate for outward passage through plasmalemma, and (b) the majority of nitrate reduction as occurring during or immediately following influx across the plasmalemma, with endogenous 14NO −3 initially moving outward being recycled inward and thereby being reduced.
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Abbreviations
- A %:
-
Atom %
References
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Paper No. 8178 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh
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MacKown, C.T., Jackson, W.A. & Volk, R.J. Partitioning of previously-accumulated nitrate to translocation, reduction, and efflux in corn roots. Planta 157, 8–14 (1983). https://doi.org/10.1007/BF00394534
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DOI: https://doi.org/10.1007/BF00394534