Effects of elevated nitrogen application on nitrogen partitioning, plant growth, grain quality and key genes involved in glutamate biosynthesis among three rice genotypes

The N absorption and assimilation is critical for the rice (Oryza sativa L.) yield increase when overdose N was applied in rice production. Three different rice genotypes, 'Quanliangyou 1' (Q1), 'Quanliangyou 681' (Q681) and 'Huanghuazhan' (HHZ), were selected to investigate the effects of elevated N input on the N partitioning, plant growth, grain quality and key genes involved in glutamate biosynthesis. Under increasing N inputs (0, 120, 180, 250 kg ha(-1)), N content in leaf, culm, seed and root were increased significantly. The increased N was preferentially deposited in leaf and culm. Tiller number, panicle number and length were also proved to be significantly promoted, but plant height and 1000-grain weight were nonsignificantly affected under elevated N input. Under high N input, seed protein content was elevated, while fatty acid and amylose content remained unchanged in comparison to low N input, but amylopectin content decreased. For the key genes in N assimilation, glutamine synthetase (OsGS1;1) could be induced by increasing N input (0 to 180 kg ha(-1)) but higher N input (250 kg ha(-1)) inhibit its expression, which showed similar response pattern with the glutamine synthetase activity. Although different rice genotypes showed similar response pattern to elevated N input, each genotype varied a lot in certain phenotypic indexes. And the response pattern of all these phenotypic characteristics to elevated N input was independent of rice genotype. These findings suggest that elevated N input could promote rice growth, reallocate N content in different tissues, and have negative impact on grain quality. This study provided physiological and molecular foundation for rice breeding and cultivation under high N input.