Characterizing the metabolites related to rice salt tolerance with introgression lines exhibiting contrasting performances in response to saline conditions

Rice is susceptible to salt stress at the seedling stage. To explore the molecular mechanisms underlying salt tolerance, the metabolic responses to salt stress were investigated with a metabolite-profiling technique. Gas chromatography-mass spectrometry was used to profile metabolite changes in five rice lines with a similar genetic background, but with obviously diverse growth performances under saline conditions. A total of 84 metabolites were detected in rice leaf extracts under control and saline conditions. The data revealed that amino acids were enriched more in three salt-tolerant lines (G58, G1710, and IR64) than in two salt-sensitive lines (G45 and G52) under control conditions, suggesting that there were basal metabolite differences between the tolerant and sensitive lines. Additionally, significantly higher allantoin levels in G58, G1710, and IR64 under both stress and control conditions were observed, implying allantoin was important for the better growth of the three rice lines. Moreover, sorbitol, melezitose, and pipecolic acid levels increased considerably in response to salt stress in the five lines, indicating they contribute to rice responses to salt stress significantly. Interestingly, the similar metabolic patterns were regulated by salt stress in the salt-sensitive and salt-tolerant lines, and the main difference was quantitative. The sensitive lines had more pronounced increases during the early stages of the stress treatment than the tolerant lines. Thus, monitoring the metabolome changes of plants may provide crucial insights into how plants tolerate stress. The results presented herein provide valuable information for further elucidating the molecular mechanisms underlying rice salt tolerance.