Effects of aluminium on nitrate uptake and assimilation

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

A study was conducted to examine the hypothesis that the effects of external Al on NO3− uptake and assimilation depend upon the concentration of Al present. Young soybean seedlings [Glycine max (L.) Merrill, cv. Essex], growing under moderate acidity stress at pH 4-2, were exposed to a range of {A13+} in solution for 3d, and to labelled 99 atom %15NO3− during the final hour of Al exposure. Uptake of 15NO3−g−1 root dry weight was increased by about 28% in the presence of Al at {A13+} below 10 mmolm−3, and NO3− uptake was decreased by about 12% when the {A13+} increased to 44mmoln−3. The stimulation phase closely paralleled stimulation of root elongation. At higher {A13+}, the inhibition of root elongation was much more severe than that of NO3− uptake. There was no indication of a separate effect of Al on root 15NO3− reduction in situ, as the accumulation of reduced 15N in the root remained a similar percentage of 15NO3− uptake at all {A13+}. At higher {A13+}, the atom %15N enrichment of the insoluble reduced-N (protein) fraction of root tips increased. This suggests that the Al inhibition of root elongation did not result from disruption of the N supply to the root apex.

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