Aluminium toxicity has been shown to decrease NO3- uptake in Zea mays
seedlings during the first 30 minutes after addition of Al3+. This sug
gests that NO3- uptake inhibition could be a primary response to Al ad
dition. We therefore tested the hypothesis that NO3- uptake and root e
longation are affected differently by Al3+. Eight-day old seedlings we
re exposed to 100 mu M Al3+ in the presence of 1 or 10 mM Ca2+, added
as either CaSO4 or CaCl2. In the presence of Al3+, cumulative uptake o
f NO3- -N during an 8 h period was not affected by Ca2+ level (1 or 10
mM). Root elongation at 1 mM Ca2+ was decreased to 63% of the control
by the presence of Al3+. Raising ambient Ca2+ from 1 to 10 mM in the
presence of Al3+ restored elongation rates to 78% (CaCl2) and 88% (CaS
O4) of elongation without Al. Because reductions in root elongation we
re partially overcome by added Ca2+, but lowered uptake of NO3- was no
t, it was concluded that Al3+ toxicity decreased root growth and NO3-
uptake by different mechanisms.