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Whole Plant Studies using Radioactive 13-Nitrogen: II. A COMPARTMENTAL MODEL FOR THE UPTAKE AND TRANSPORT OF NITRATE IONS BY Zea mays 总被引:1,自引:0,他引:1
Nitrate ion uptake by the roots of hydroponically grown maizeseedlings was measured using the short-lived isotope 13N. Itis shown to be described by a four compartment model, recognizablynitrogen in the root bathing solution, nitrogen which is readilyexchangeable from the root, nitrogen bound in the root, andnitrogen transported from the root. Some of the absorbed activity leaks back into the root bathingsolution with the efflux from the root, as a fraction of theinflux, increasing with concentration to be greater than 08at external nitrate ion concentrations above about 1.0 mol m3.The capacity of the exchangeable root pool increases with externalnitrate ion concentration, approaching the expected cytoplasmicnitrate ion content at the highest external nitrate ion concentrationsstudied (70 mol m3). The investigation has highlighted the problems of interpretinguptake profiles in experiments for which the 10 min half-lifeof 13N dictates experimental times that are comparable withthe times for saturation of root pools. Key words: Zea mays, 13N, Compartmental model, Nitrate uptake 相似文献
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Methods are described for studying the uptake, by hydroponicallygrown Zea mays seedlings, of ammonium and nitrate ions labelledwith radioactive nitrogen-13, which has a half-life often minutes.For nitrate only, some of the activity absorbed by the rootexchanges back out again into the root bathing solution. Theamount of this activity is about five times too large to beattributable to exchange with ions in the root cortical apoplasm.Much of it must be transferred from the root symplasm with ahalf-time of exchange of 25 min. After exposing the rootto the labelled solution, equilibrium rates of transport to,and distribution in the shoot were attained within 2 min, fornitrate, or 5 min, for ammonium. The pools within the root,and the transport pathway through which the label passes musttherefore rapidly attain the specific activity of the nutrientsolution. Distribution patterns through the plant are reasonablyconsistent with earlier work on nitrogen assimilation and transport. Key words: Zea mays, Nitrate uptake, Amonium uptake, 13N tracer 相似文献
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Nitrogen-13 labelled nitrate and ammonium ions were used tomeasure uptake and assimilation rates in non-destructive experimentsin which the water flux through hydroponically grown maize plantswas doubled by changing the ambient humidity. Although no immediateeffects on ion uptake were observed, longer term observationsshowed different patterns of coupling for the uptake parametersfor nitrate and for ammonium. The patterns were compared withpatterns predicted for different combinations of processes foruptake and for discharge to the xylem. Those which were compatiblewith the experimental patterns indicated that for nitrate theuptake into the root showed coupling to water flux whereas dischargeto the xylem did not. For ammonium there appeared to be couplingto the water flux of both uptake into the root and of dischargeto the xylem though it was less evident in the former when theexternal ammonium ion concentration was low. Key words: Ion-water coupling, Ammonium uptake, Nitrate uptake 相似文献
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Whole Plant Studies using Radioactive 13-Nitrogen: IV. A COMPARTMENTAL MODEL FOR THE UPTAKE AND TRANSPORT OF AMMONIUM IONS BY ZEA MAYS 总被引:1,自引:0,他引:1
Presland, M. R. and McNaughton, G. S. 1986. Whole plant studiesusing radioactive 13-nitrogen IV. A compartmental model forthe uptake and transport of ammonium ions by Zea mays.Jexp. Bot. 37: 16191632 Ammonium ion uptake by roots of hydroponically grown maize seedlingsand the transport of ammonium-sourced nitrogen to the shootwere measured using the short-lived isotope 13-nitrogen. Theyare shown to be described by a five compartment modelammoniumin the root bathing solution, ammonium entering the root, nitrogenbound in the root, nitrogen outside the load region but stillwithin the root, and nitrogen in the shoot. Once taken intothe root symplasm, ammonium-sourced nitrogen was not exchangedwith the external solution. Activity-time profiles for nitrogentransported both basally and apically from the load region ofthe root implied the existence of large well-mixed pools inthe transport path, though the capacity of the pools inferredfrom modelling the profiles was greater than found by dissectingroots following loading with labelled ammonium. Key words: Ammonium uptake, Zea mays, compartmental model, 13-nitrogen 相似文献
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