Rice is being increasingly cultivated in intermittently irrigated regions and also in aerobic soil in which Nitrate (NO−
3
)
plays important role in nutrition of plant. However, there is no information regarding the influence of nitrate on the overall
growth and uptake of nitrogen (N) in rice plant. Solution culture experiments were carried out to study the effects of NO−
3
on the plant growth, uptake of N, and uptake kinetics of NH+
4
in four typical rice (Oryza sativa L.) cultivars (conventional
indica, conventional japonica, hybrid indica, and hybrid japonica), and on plasma membrane potential in roots of two
conventional rice cultivars (indica and japonica) at the seedling stage. The results obtained indicated that a ratio of
50/50 NH+
4
-N/NO−
3
-N increased the average biomass of rice shoots and roots by 20% when compared with that of 100/0
NH+
4
-N/NO−
3
-N. In case of the 50/50 ratio, as compared with the 100/0 ratio, total N accumulated in shoots and roots
of rice increased on an average by 42% and 57%, respectively. Conventional indica responds to NO−
3 more than any other
cultivars that were tested. The NO−
3
supply increased the maximum uptake rate (Vmax) of NH+
4
by rice but did not
show any effect on the apparent Michaelis-Menten constant (Km) value, with the average value of Vmax for NH+
4
among
the four cultivars being increased by 31.5% in comparison with those in the absence of NO−
3
. This suggested that NO−
3
significantly increased the numbers of the ammonium transporters. However, the lack of effect on the Km value also
suggested that the presence of NO−
3
had no effect on the affinity of the transporters for NH+
4
. The plasma membrane
potential in the roots of conventional indica and japonica were greatly increased by the addition of NO−
3
, suggesting that
NO−
3
could improve the uptake of N by roots of the rice plant. In conclusion, the mechanisms by which NO−
3
enhances
the growth and N uptake of rice plant was found by the increased value of Vmax of NH+
4
and increased plasma membrane
potential. Thus promotion of nitrification in paddy soil is of great significance for improving the production of rice.
Rice is being increasingly cultivated in intermittently irrigated regions and also in aerobic soil in which Nitrate (NO−3)plays important role in nutrition of plant. However, there is no information regarding the influence of nitrate on the overallgrowth and uptake of nitrogen (N) in rice plant. Solution culture experiments were carried out to study the effects of NO−3on the plant growth, uptake of N, and uptake kinetics of NH+4in four typical rice (Oryza sativa L.) cultivars (conventionalindica, conventional japonica, hybrid indica, and hybrid japonica), and on plasma membrane potential in roots of twoconventional rice cultivars (indica and japonica) at the seedling stage. The results obtained indicated that a ratio of50/50 NH+4-N/NO−3-N increased the average biomass of rice shoots and roots by 20% when compared with that of 100/0NH+4-N/NO−3-N. In case of the 50/50 ratio, as compared with the 100/0 ratio, total N accumulated in shoots and rootsof rice increased on an average by 42% and 57%, respectively. Conventional indica responds to NO−3 more than any othercultivars that were tested. The NO−3supply increased the maximum uptake rate (Vmax) of NH+4by rice but did notshow any effect on the apparent Michaelis-Menten constant (Km) value, with the average value of Vmax for NH+4amongthe four cultivars being increased by 31.5% in comparison with those in the absence of NO−3. This suggested that NO−3significantly increased the numbers of the ammonium transporters. However, the lack of effect on the Km value alsosuggested that the presence of NO−3had no effect on the affinity of the transporters for NH+4. The plasma membranepotential in the roots of conventional indica and japonica were greatly increased by the addition of NO−3, suggesting thatNO−3could improve the uptake of N by roots of the rice plant. In conclusion, the mechanisms by which NO−3enhancesthe growth and N uptake of rice plant was found by the increased value of Vmax of NH+4and increased plasma membranepotential. Thus promotion of nitrification in paddy soil is of great significance for improving the production of rice.
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