Ammonium Enables Aluminum-Induced Stimulation of Nitrogen Assimilation in Roots of Al-Tolerant Maize Genotypes

Abstract

One aluminum (Al)-sensitive (B-73) and two Al-tolerant (F-2 and L-2039) maize genotypes were subjected to Al stress (100 μM Al) under two nitrogen (N) treatments [13.2 mM nitrate (NO3−) and 8.3 mM NO3− + 4.9 mM ammonium (NH4+)]. Growth parameters, chlorophyll, root N and NO3− contents, root nicotinamide adenine dinucleotide (NADH-) and nicotinamide adenine dinucleotide phosphate (NADPH)-nitrate reductase, glutamine synthetase, and glutamate dehydrogenase activities were determined. Aluminum significantly decreased growth and chlorophyll content in Al-sensitive genotype. Nitrate accumulation in roots was increased by Al in tolerant plants. In the sensitive genotype, Al suppressed all enzymes in NO3− plants, while in NO3−/NH4+ plants the suppression was less severe, and NADPH-nitrate reductase was even stimulated. In tolerant NO3−plants, glutamate dehydrogenase was stimulated in F-2 and glutamine synthetase suppressed in L-2039 genotype. In tolerant NO3−/NH4+- plants, all enzymes were stimulated by Al, which may be attributed to their participation in defense mechanisms.