Evaluating the significance of amino acids (AAs) in cyanide-treated rice plants under different nitrogen fertilization using the relative importance index of AA.

The biosynthesis of amino acids (AAs) in plants is affected by different nitrogen (N) sources. The effects of exogenous cyanide (KCN) on the concentrations and profiles of AAs in rice seedlings were carried out in the presence of nitrate (+NO)/ammonium (+NH) or N deficiency (-N). Targeted metabolomics analysis indicated that the highest accumulation of AAs in CN-treated rice seedlings was detected in the "CN+NH" treatments than in other treatments, wherein the doses of exogenous KCN did not significantly affect the total amount of AAs in rice seedlings at the same N fertilized condition. The total content of AAs in rice shoots under "CN+NH" treatments was higher than other treatments, while the total content of AAs in rice roots under "CN+NO" treatments was higher than other treatments. Also, the profiles of 21 AAs in CN-treated rice seedlings showed tissue-specific under different N fertilization. The relative importance index (RII) of AA was used to evaluate the importance of AAs in CN-treated rice seedlings under different N fertilization. The common AAs with higher RII values were compared between three different treatments of KCN (e.g., 0, 1, and 2 mg CN/L). Under "CN+(-N)" treatments, Ala, Asp, Glu, Val, and Gly (Ala, Gly, Val, and Lys) were the common AAs in rice roots (shoots). Under "CN+NO" treatments, Ala, Glu, Asp, Ser, and Thr (Asp, Ala, Thr, Ser, and Asn) were the common AAs with higher RII values in rice roots (shoots) between all CN treatments. Under "CN+NH" treatments, Asp, Gln, Asn, and Ala (Asp, Glu, and Thr) were the common AAs with higher RII values in rice roots (shoots) between all CN treatments. These results suggested that using the RII to describe the change and fluctuation of AAs in rice plants may reflect the different N utilization strategies in response to exogenous CN exposure.