Physiological Processes Contributing to the Difference in Grain Amino Acid Content between Two Hybrid Rice (Oryza sativa L.) Cultivars

Improving grain amino acid content of rice (Oryza sativa L.) is essential for the health of consumers. This study was conducted to identify the physiological processes that contribute to the higher grain amino acid content in hybrid rice cultivar Lingliangyou 268 compared to Luliangyou 996. The results showed that total amino acid content in grains was 9% higher in Lingliangyou 268 than in Luliangyou 996. There was no significant difference in grain nitrogen (N) content between Lingliangyou 268 and Luliangyou 996, while ratio of amino acid to N was 6% higher in Lingliangyou 268 compared to Luliangyou 996. A total of 16 differentially expressed proteins related to amino acid metabolism (e.g., erythronate-4-phosphate dehydrogenase domain containing protein) were identified in grains between Lingliangyou 268 and Luliangyou 996. The identified proteins were involved in 10 molecular functions. Six of the 10 defined functions were related to binding (heterocyclic compound binding, nucleoside phosphate binding, nucleotide binding, organic cyclic compound binding, protein binding, and small molecule binding) and the other 4 defined functions were catalytic activity, enzyme regulator activity, hydrolase activity, and transferase activity. These results indicate that the higher grain amino acid content in Lingliangyou 268 compared to Luliangyou 996 is attributed to increased efficiency of converting N to amino acid that results from altered expression of proteins related to amino acid metabolism.