Whole Plant Studies using Radioactive 13-Nitrogen

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Abstract
Presland, M. R. and McNaughton, G. S. 1986. Whole plant studies using radioactive 13-nitrogen IV. A compartmental model for the uptake and transport of ammonium ions by Zea mays.—J exp. Bot. 37: 1619–1632 Ammonium ion uptake by roots of hydroponically grown maize seedlings and the transport of ammonium-sourced nitrogen to the shoot were measured using the short-lived isotope 13-nitrogen. They are shown to be described by a five compartment model—ammonium in the root bathing solution, ammonium entering the root, nitrogen bound in the root, nitrogen outside the load region but still within the root, and nitrogen in the shoot. Once taken into the root symplasm, ammonium-sourced nitrogen was not exchanged with the external solution. Activity-time profiles for nitrogen transported both basally and apically from the load region of the root implied the existence of large well-mixed pools in the transport path, though the capacity of the pools inferred from modelling the profiles was greater than found by dissecting roots following loading with labelled ammonium.