Abstract:

【Objective】To reveal the influence of salt stress on metabolites and metabolism pathway in the rice seed of Changbai 10, understand the mechanism of its salt tolerance, and screen possible markers for salt tolerant rice varieties. 【Method】Gas chromatography-mass spectrometry (GC-MS) was used to analyze the changes of metabolites in the seeds (25 days after flower) of a saline tolerance japonica rice Changbai 10 under salt stress (4‰). The rice variety Yandao 8 with moderate salt tolerance was treated with the metabolite which was the highest improvement among the different metabolites to identify whether it could improve the salt tolerance. The treatment methods were as follows: Yandao 8 seeds were soaked in NaCl solution (5‰) containing the metabolite with different concentration gradient (0-400 mg·L^-1), after 20 hours, the seeds were put in germination box for germination test.【Result】A total of 295 metabolites were detected in the samples. Principal component analysis (PCA) and orthogonal partial least-squares-discriminant analysis OPLS-DA were performed to visualize the metabolic difference among experimental groups. The results revealed a total of 71 metabolites were significantly changed (42 up-regulated and 29 down-regulated) under salt stress. The top ten up-regulated metabolites were 5-hydroxynorvaline (5.23 fold), Pentane-1,2,5-triol (4.10 fold), Cyanoalanine (2.97 fold), L-asparagine (2.91 fold), 2-hydroxybutanoic acid (2.86 fold), Oxoglutaric acid (2.74 fold), Pyruvic acid (2.50 fold), Ornithine (2.40 fold), Citrulline (2.07 fold), Proline (1.94 fold). And the top ten down-regulated metabolites were Erythrose (2.83 fold), Xylonolactone (2.49 fold), Aspartate (2.42 fold), Uridine 5’-monophosphate (2.37 fold), Cholesterone (1.90 fold), Hexaric acid (1.87 fold), D7-glucose (1.86 fold), 5,7-dihydroxy-4’-methoxyisoflavone (1.72 fold), Amidosulfonic acid (1.61 fold), 6-deoxygalactofuranose (1.61 fold). Among them, 15 differential metabolites were KEGG annotated and significantly(P<0.01) affected arginine biosynthesis, alanine, aspartate and glutamate metabolism, butanoate metabolism, carbon metabolism, lysine degration, biosynthesis of amino acids, glyoxylate and dicarboxylate metabolism, citrate cycle (TCA cycle) and so on. The germination rate of Yandao 8 was only 66.7% under salt stress (5‰), significantly lower than that with exogenous 5-hydroxynvaline treatment (74.3-90.3%). The result revealed that germination rate of the seeds with 200 mg·L^-1 5-hydroxynvaline treatment was the highest.【Conclusion】Amino acid and organics acid were mainly up regulated, while sugar and lipid were mainly down regulated in salt treated group. The changed metabolism pathway of Arginine biosynthesis and TCA cycle might contribute to its high salt tolerance. 5-hydroxynvaline could effectively alleviate the inhibition of salt stress on rice seeds germination, and the optimal concentration is 200 mg·L^-1.

Key words: salt stress, metabolome, differential metabolite, metabolic pathway, GC-MS, rice