Genotypic variations in nitrate respiration along with potassium nitrate treatment - accountable for water logging tolerance in maize

The present investigation was undertaken to study the effects of water logging and potassium nitrate treatment on the status of nitrate metabolism in maize genotypes, I 167 and LM 5, showing differential tolerance towards water logging stress. Water logging reduced length and biomass of LM 5 (stress susceptible) seedlings to a higher extent than those of I 167 (stress tolerant). Foliar spray of 1% KNO 3 increased seedling growth in both the genotypes. The water logged I 167 seedlings maintained their nitrate levels more efficiently than those of LM 5 seedlings. The parallel increase in NO content in the hypoxic roots showed the effective utilization of NO in nitrate respiration pathway of I 167 seedlings. The increased NO content in the shoots of water logged LM 5 seedlings irrespective of their reduced NR activity showed that the susceptible genotype might have preferentially utilized nitrite ions for NO generation rather than ammonium assimilation during early stage of water logging stress. KNO 3 spray increased alanine amino transferase (AlaAT) and glutamine oxoglutarate amino transferase (GOGAT) activities along with an increase in amino acid and protein content of I 167 shoots that might be responsible for better assimilation of amino acids in the tolerant genotype. It may thus be concluded that there were genotypic differences in nitrate metabolism under water logging stress and potassium nitrate significantly improved ammonium assimilation of maize genotypes.