ISSN:
1365-3040
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Biologie
Notizen:
We compared influxes and internal transport in soybean plants (Glycine max cv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope15N and the radioactive isotope13N. The objective was to see whether mass spectrometric determinations of tissue 15N content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using 15N or 13N measurements with either NO3/− or NH4+ at 4 or 2 mol−3, respectively in the external solution. (2) Transport to the shoot of N from NO3 absorbed over a 5–15 min period could be monitored when the external NO3− concentration ranged from 0–05 to 4 mol m−3. NH4+ as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with 13N. (3) Influx of NO3− into root tissue could be measured by 15N enrichment after 5–10 min at concentrations approaching the probable KM of the high-affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3− is the N source.For many purposes, 15N tracing can be used satisfactorily to estimate influxes of both NO3− and NH4+ in soybean roots. Use of the short-lived radio nuclide 13N remains the method of choice for more refined measurements of internal distribution and assimilation.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1365-3040.1996.tb00422.x
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