Amino acid composition of leaf, grain and bracts of japonica rice (Oryza Sativa ssp japonica) and its response to nitrogen fertilization

This study aims to elucidate the role of bracts of rice spikelets in terms of nitrogen (N) remobilization, focusing on amino acid (AA). A pot experiment with three treatments of N rate was performed, using the japonica rice cultivar Ningjing5 as material. Dynamic changes of AA, mainly the protein amino acids, in leaf, grain, and bracts were monitored, and the redistribution rate of protein-N from leaf and bracts and its contribution rate to grain protein-N were calculated accordingly. Results showed that the amino acid composition of bracts were similar to that of leaf, but quite different from that of grain. In response to N, AAs in leaf and bracts were more sensitive to N fertilizer than those in grain. High protein-N redistribution rate of leaf and bracts was observed, being 69.88, 69.62 and 67.42% for leaf, bracts of superior spikelets and inferior spikelets, respectively. N fertilization significantly increased the redistribution rate of leaf protein-N. Averaged contribution rate of leaf protein-N to grain was 23.38%. Notably, a substantial contribution rate of protein-N in bracts was detected, with the mean values being 10.19 and 9.77% for bracts of superior spikelets and inferior spikelets, respectively. These findings collectively suggest that bracts of rice spikelets be a major source of N remobilization for grain filling, and their importance be acquired when exploring the mechanism underlying nitrogen use efficiency.