Expression of genes related to nitrogen metabolism in maize grown under organic and inorganic nitrogen supplies.

Application of organic nitrogen (N) has been proposed as a method to reduce potential environmental pollution due to N loss without sacrificing grain yield. The mechanism responsible for organic N regulation of maize (Zea maysL.) N metabolism is nonetheless largely unknown. In this study, we compared the expression of genes related to N assimilation and remobilization during the grain filling stage in maize plants grown under field conditions. We applied five different N treatments, which consisted of N supplied in organic and/or inorganic forms at the following rates: 0/45, 0/120, 0/240, 120/120, and 240/0 kg ha−1organic/inorganic N. Yield was found to increase with increasing N input, but no significant difference was found in grain yield among 0/240, 240/0 and 120/120 treatments. Organic N application tended to decrease N accumulation and to increase N utilization efficiency. Genes related to N assimilation activity in leaves, such asZmNR1andZmFd-GOGAT1, were unaffected by different N forms. In contrast, genes related to N remobilization activity in leaves, such asZmGS1.1andZmGDH1, were up-regulated, especially in old leaves, by the pure organic N supply treatment (240/0). These data suggest that application of pure organic N likely induces a N-deficiency response in maize plants, with a consequent increase in physiological N utilization efficiency due to up-regulation of key genes involved in N remobilization processes. [ABSTRACT FROM PUBLISHER]