Metabolomic analysis of chilling response in rice (Oryza sativa L.) seedlings by extractive electrospray ionization mass spectrometry

Chilling stress is a major production threat for rice ( Oryza sativa L.). The mechanism of chilling response has not been unveiled up to now, especially at the metabolomic level. In this study, two Asian rice cultivars, Qiutianxiaoting (chilling-tolerant variety) and 93−11 (chilling-susceptible variety), were used to analyze the metabolic changes when exposed to low temperature and recovered by extractive electrospray ionization mass spectrometry (EESI-MS). Physiological and metabolic analysis combining with bioinformatics were performed to reveal cold resistance mechanism of these two varieties. Physiological analysis showed that only Qiutianxiaoting survived after 36 h chilling treatment, and the growth indexes of Qiutianxiaoting took on a decreasing trend, but these indexes of 93−11 appeared a trend of increase under cold treatment; moreover, the levels of antioxidant activities (SOD, POD and CAT) were higher in Qiutianxiaoting than 93−11, especially at recovery stage. PCA and OPLS-DA analysis all showed that Qiutianxiaoting, not 93−11, could be separated with each other under chilling stress, which indicated that these two subspecies of rice had different mechanisms to resist cold temperature. The results of metabolic analysis indicated that low temperature activated phenylpropanoid biosynthesis and flavone and flavonol biosynthesis in 93−11, while it induced the expression of methyl jasmonate biosynthesis-related genes in Qiutianxiaoting, which might mitigate chilling damage and effectively make it more cold-resistant than 93−11. This study would shed some lights on the cold resistance mechanism of these two rice cultivars in terms of physiological and metabolic analysis.