Aluminum Effects on Nitrogen Uptake and Nitrogen Assimilating Enzymes in Maize Genotypes with Contrasting Tolerance to Aluminum Toxicity

Abstract The objective of this study was to investigate the effect of aluminum (Al) on NO3 − and NH4 + uptake and on activity/expression of the N‐assimilating enzymes glutamine synthetase (GS1, GS2, and GSr isoforms, EC 6.3.1.2), glutamate synthase (NADH‐GOGAT, EC 1.4.7.14; ferredoxin‐GOGAT, EC 1.4.7.1), and glutamate dehydrogenase (GDH, EC 1.4.1.2) of maize (Zea mays L.) genotypes contrasting in tolerance to Al toxicity. Seeds were germinated on paper towels, screened for uniformity and allowed to grow for 5–6 d in a modified Steinberg nutrient solution, pH 5.5, in a glasshouse, under natural light. Immediately after transference to a growth chamber (12 h photoperiod, 26°C ± 0.5/18°C ± 0.9 day/night temperature, 72% RH and 540 µ Em−2 s−1 quantum flux density) Al stress was imposed by lowering pH to 4.5 and addition of 166 µmoles L−1 AlCl3. Control plants were grown in the same nutrient solution without Al, pH 4.5. Aluminum inhibited NO3 − and NH4 + uptake and decreased shoot dry matter yield in all genot...