The sensory quality of green tea changes greatly within a single spring season, but the mechanism is not clearly elucidated. Young shoots of the early, middle, and late spring season were subjected to metabolite profiling using gas chromatography-time-of-flight mass spectrometry (TOF/MS) and ultraperformance liquid chromatography-quadrupole-TOF/MS. Multivariate analyses revealed largely different metabolite phenotypes in young shoots among different periods. The contents of amino acids decreased, whereas carbohydrates, flavonoids and their glycosides, tricarboxylic acid cycle, and photorespiration pathways were strongly reinforced in the late spring season, which were well reflected in the sensory quality of made teas. Metabolomic analyses further demonstrated distinct variations of metabolite phenotypes in mature leaves. The results suggested that the fluctuation of green tea quality in the spring season was caused by changes of metabolite phenotypes in young shoots, which was likely related to the remobilization of carbon and nitrogen reserves from mature leaves.

BackgroundNitrogen (N) plays an important role in the formation of tea quality-related compounds, like amino acids and flavor/aroma origin compounds. Lipids, which have been reported to be affected by N deficiency, are precursors to the generation of flavor/aroma origin compounds in tea plant. However, there is no literature about the lipid profiles of tea plant affected by N fertilization. Hence, we hypothesize that the biosynthesis of flavor-related compounds in tea was affected by N through its regulation of lipid metabolism.ResultsIn this study, mature leaves and new shoots of tea plant grown under three N levels at the rates of 0, 285 and 474 kg/ha were applied for ultra-performance liquid chromatography-mass spectrometry (UPLC/MS) based lipidomic analysis. Totally, 178 lipid species were identified. The results showed that the composition of lipid compounds in mature leaves and new shoots varied dramatically, which was also affected by N levels. The higher content of the storage lipid TAG and higher carbon (C)/N ratio in mature leaves than that of new shoots in tea plants grown under low N level (0 kg/ha) suggested that tea plants could remobilize the C stored in TAG to maintain their C/N balance and help to improve the quality of tea. N fertilization resulted in a higher content of the compounds 36:6 MGDG and 36:6 DGDG. Since these compounds contain linolenic acid (18:3), a precursor to the formation of aroma origin compounds, we suggested their increase could contribute to the quality of tea.ConclusionsTaken together, the present work indicated that appropriate application of N fertilizer could balance the lipid metabolism and the formation of flavor/aroma origin compounds, which help to improve the quality of tea. Moreover, excess N fertilization might deteriorate the aroma quality of made tea due to increases of precursors leading to grassy odor.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1111-6) contains supplementary material, which is available to authorized users.

BackgroundAs the predominant secondary metabolic pathway in tea plants, flavonoid biosynthesis increases with increasing temperature and illumination. However, the concentration of most flavonoids decreases greatly in light-sensitive tea leaves when they are exposed to light, which further improves tea quality. To reveal the metabolism and potential functions of flavonoids in tea leaves, a natural light-sensitive tea mutant (Huangjinya) cultivated under different light conditions was subjected to metabolomics analysis.ResultsThe results showed that chlorotic tea leaves accumulated large amounts of flavonoids with ortho-dihydroxylated B-rings (e.g., catechin gallate, quercetin and its glycosides etc.), whereas total flavonoids (e.g., myricetrin glycoside, epigallocatechin gallate etc.) were considerably reduced, suggesting that the flavonoid components generated from different metabolic branches played different roles in tea leaves. Furthermore, the intracellular localization of flavonoids and the expression pattern of genes involved in secondary metabolic pathways indicate a potential photoprotective function of dihydroxylated flavonoids in light-sensitive tea leaves.ConclusionsOur results suggest that reactive oxygen species (ROS) scavenging and the antioxidation effects of flavonoids help chlorotic tea plants survive under high light stress, providing new evidence to clarify the functional roles of flavonoids, which accumulate to high levels in tea plants. Moreover, flavonoids with ortho-dihydroxylated B-rings played a greater role in photo-protection to improve the acclimatization of tea plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-1012-8) contains supplementary material, which is available to authorized users.

The qualities of tea (Camellia sinensis) are not clearly understood in terms of integrated leading molecular regulatory network mechanisms behind inorganic phosphate (Pi) limitation. Thus, the present work aims to elucidate transcription factor-dependent responses of quality-related metabolites and the expression of genes to phosphate (P) starvation. The tea plant organs were subjected to metabolomics analysis by GC×GC-TOF/MS and UPLC-Q-TOF/MS along with transcription factors and 13 metabolic genes by qRT-PCR. We found P starvation upregulated SPX2 and the change response of Pi is highly dependent on young shoots. This led to increased change in abundance of carbohydrates (fructose and glucose), amino acids in leaves (threonine and methionine), and root (phenylalanine, alanine, tryptophan, and tyrosine). Flavonoids and their glycosides accumulated in leaves and root exposed to P limitation was consistent with the upregulated expression of anthocyanidin reductase (EC 1.3.1.77), leucoanthocyanidin dioxygenase (EC 1.4.11.19) and glycosyltransferases (UGT78D1, UGT78D2 and UGT57L12). Despite the similar kinetics and high correlation response of Pi and SPX2 in young shoots, predominating theanine and other amino acids (serine, threonine, glutamate, valine, methionine, phenylalanine) and catechin (EGC, EGCG and CG) content displayed opposite changes in response to Pi limitation between Fengqing and Longjing-43 tea cultivars.

The chlorotic tea variety Huangjinya, a natural mutant, contains enhanced levels of free amino acids in its leaves, which improves the drinking quality of its brewed tea. Consequently, this chlorotic mutant has a higher economic value than the non-chlorotic varieties. However, the molecular mechanisms behind the increased levels of free amino acids in this mutant are mostly unknown, as are the possible effects of this mutation on the overall metabolome and biosynthetic pathways in tea leaves. To gain further insight into the effects of chlorosis on the global metabolome and biosynthetic pathways in this mutant, Huangjinya plants were grown under normal and reduced sunlight, resulting in chlorotic and non-chlorotic leaves, respectively; their leaves were analyzed using transcriptomics as well as targeted and untargeted metabolomics. Approximately 5,000 genes (8.5% of the total analyzed) and ca. 300 metabolites (14.5% of the total detected) were significantly differentially regulated, thus indicating the occurrence of marked effects of light on the biosynthetic pathways in this mutant plant. Considering primary metabolism, including that of sugars, amino acids, and organic acids, significant changes were observed in the expression of genes involved in both nitrogen (N) and carbon metabolism. The suite of changes not only generated an increase in amino acids, including glutamic acid, glutamine, and theanine, but it also elevated the levels of free ammonium, citrate, and α-ketoglutarate, and lowered the levels of mono- and di-saccharides and of caffeine as compared with the non-chlorotic leaves. Taken together, our results suggest that the increased levels of amino acids in the chlorotic vs. non-chlorotic leaves are likely due to increased protein catabolism and/or decreased glycolysis and diminished biosynthesis of nitrogen-containing compounds other than amino acids, including chlorophyll, purines, nucleotides, and alkaloids.

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