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In order to explore the difference of metabolites before and after tea tree grafting, tea tree grafting was carried out by cutting and grafting method using "Peach-shaped leaf" as the scion and "Short-grafted pekoe" as the rootstock. Substances in tea plants before and after grafting were detected by using broad-targeted metabolomics technology, and multivariate statistical methods such as principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used to study the difference of metabolites before and after grafting. The results showed that a total of 804 metabolites were detected in tea samples before and after grafting, of which 105 metabolites were significantly different; Compared with that before grafting, 44 differential metabolites were significantly up-regulated in tea samples after grafting, and 61 differential metabolites were significantly down-regulated, and the number of differential metabolites down-regulated was greater than that up-regulated; In addition, the study on KEGG metabolic pathways revealed that these differential metabolites were mainly distributed in 20 metabolic pathways including purine metabolism, nicotinate and nicotinamide metabolism, glycerol phosphatide metabolism, flavonoid biosynthesis, flavonoid and flavonol biosynthesis, carbon sequestration by photosynthetic organisms, caffeine metabolism, and biosynthesis of secondary metabolites. Among them, there were 24 differential metabolites annotated by KEGG, which were dominated by flavone, nucleotides and their derivatives. In addition, most flavonoids in the pathways were significantly up-regulated, while nucleotides and their derivatives were significantly down-regulated. In conclusion, the content of metabolites of the variety "Peach-shaped leaf" is significantly changed after grafting, which can provide a theoretical reference for the processing and production of grafted tea leaves to a certain extent.

Panax notoginseng saponins (PNSs) are used as industrial raw materials to produce many drugs to treat cardio-cerebrovascular diseases. However, it is a heat-sensitive plant, and its large-scale artificial cultivation is impeded by high temperature stress, leading to decreases in productivity and PNSs yield. Here, we examined exogenous foliar leucine to alleviate heat stress and explored the underlying mechanism using metabolomics. The results indicated that 3 and 5 mM exogenous foliar leucine significantly alleviated heat stress in one-year- and two-year-old P. notoginseng in pots and field trials. Exogenous foliar leucine enhanced the antioxidant capacity by increasing the activities of antioxidant enzymes (POD, SOD) and the contents of antioxidant metabolites (amino acids). Moreover, exogenous foliar leucine enhanced carbohydrate metabolism, including sugars (sucrose, maltose) and TCA cycle metabolites (citric acid, aconitic acid, succinic acid and fumaric acid), in P. notoginseng leaves, stems, and fibrous roots to improve the energy supply of plants and further alleviate heat stress. Field experiments further verified that exogenous foliar leucine increased the productivity and PNSs accumulation in P. notoginseng. These results suggest that leucine application is beneficial for improving the growth and quality of P. notoginseng under heat stress. It is therefore possible to develop plant growth regulators based on leucine to improve the heat resistance of P. notoginseng and other crops.