Liu Mei-Ya, Burgos Asdrubal, Ma Lifeng, Zhang Qunfeng, Tang Dandan, Ruan Jianyun
Key Laboratory of Tea Plant Biology and Resources Utilization (Ministry of Agriculture), Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, 310008, China.
Max Planck Institute of Molecular Plant Physiology, 14476, Potsdam-Golm, Germany.
BMC Plant Biol. 2017 Oct 16;17(1):165. doi: 10.1186/s12870-017-1111-6.
Nitrogen (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.
In 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.
Taken 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.
氮（N）在茶叶品质相关化合物的形成中起着重要作用，如氨基酸和风味/香气源化合物。脂质是茶叶中风味/香气源化合物生成的前体，据报道会受到氮素缺乏的影响。然而，目前尚无关于氮肥对茶树脂质谱影响的文献报道。因此，我们推测氮素通过调节脂质代谢影响茶叶中风味相关化合物的生物合成。
在本研究中，对在0、285和474 kg/ha三个氮水平下生长的茶树成熟叶片和新梢进行了基于超高效液相色谱 - 质谱联用（UPLC/MS）的脂质组学分析。共鉴定出178种脂质种类。结果表明，成熟叶片和新梢中脂质化合物的组成差异显著，且受氮水平影响。在低氮水平（0 kg/ha）下生长的茶树中，成熟叶片中储存脂质TAG的含量较高，碳（C）/氮比也高于新梢，这表明茶树可以调动TAG中储存的碳来维持其碳/氮平衡，并有助于提高茶叶品质。施氮肥导致36:6 MGDG和36:6 DGDG化合物含量增加。由于这些化合物含有亚麻酸（18:3），是香气源化合物形成的前体，我们认为它们的增加有助于提高茶叶品质。
综上所述，本研究表明适当施用氮肥可以平衡脂质代谢和风味/香气源化合物的形成，有助于提高茶叶品质。此外，过量施氮可能会因导致青草气味的前体物质增加而使制成茶的香气品质下降。
