Distinctive Characteristics of Nitrogen Metabolism in Teosinte Versus Modern Maize for Water-Logging Tolerance

Water logging leads to reduction in soil oxygen, compromising the development and growth of the plant and thus results in serious yield losses. Enzymes involved in nitrogen metabolism play an important role during water logging. Therefore, this investigation was undertaken to evaluate nitrogen metabolism in maize and its wild progenitor (teosinte) under water-logging stress. Accessions of teosinte (Acc.1 and Acc.2) from two geographical locations and maize genotypes PMH-1 (relatively susceptible) and I-172 (relatively tolerant) were taken for the study. Teosinte accessions exhibited unique stress tolerance behavior by maintaining unaltered nitrate, nitrite, and nitric oxide (NO) contents in their shoots. Acc.2 revealed unaltered nitrate and NO contents in its roots during water logging. Acc.1 recorded highest nitrate, nitrite, and NO contents in its roots under stress conditions. I-172 seedlings also maintained unaltered nitrate and high NO contents under water-logging stress. The unaffected glutamate dehydrogenase (GDH) activity in hypoxic roots of I-172 suggested that it could maintain its glutamate pools under stress conditions. The seedlings of Acc.1 and Acc.2 remained unaffected with respect to their glutamine oxoglutarate amino transferase (GOGAT) activity during water logging. GOGAT activity was significantly reduced in water-logged maize genotypes but the values remained higher in the tolerant (I-172) as compared to the susceptible (PMH-1) genotype. The reduction in both GDH and GOGAT activities in PMH-1 roots might be responsible for the increased susceptibility of the genotype toward stress. Biplots of principal component analysis for the biochemical parameters showed that contents of nitrate, nitrite, and total free amino acids and activities of nitrate reductase (NR) and nitrite reductase (NiR) in hypoxic roots contributed significantly toward water-logging response of the plants. Acc.1, Acc.2, I-172 and PMH-1 seedlings showed differential behavior toward stress tolerance by occupying distinct positions on the graph. NR activity and content of crude proteins in shoots contributed significantly toward the variation in stress tolerance response of the genotypes.