Total lipids of tea plants
Glycerolipids are the most abundant lipids in plants, including phospholipids, glycolipids and neutral lipids. In this study, 156 lipid species were detected, including 16 digalactosyl glycerol (DGDG), 16 monogalactosyldiglycerol (MGDG), 13 phosphatidylglycerol (PG), 5 lysophosphatidyl glycerol (LPG), 6 lysophosphatidylcholine (LPC), 5 lysophosphatidylethanolamine (LPE), 20 phosphatidylcholine (PC), 23 phosphatidylethanolamine (PE), 14 phosphatidylinositol (PI), 26 phosphatidylserine (PS), and 12 phosphatidylic acids (PA) (Additional file 1: Table S1).
The total lipid contents of Baijiguan and Rougui at day zero were 164.323 and 45.008 nmol/mg dry weight, which showed that BJG has much more total lipids than RG (Fig. 6B). In all treatments, the total lipid content of Baijiguan decreased sharply. But all the total lipids detected in RG kept stable during the period,which showed that the lipid metabolism was different between BJG and RG.
Glycolipid changes of Baijiguan and Rougui
MGDG and DGDG are the main components of thylakoid membrane in plants. The content of MGDG and DGDG in Baijiguan and Rougui showed the same trends as those of total lipids. (Fig. 7A and B). MGDG and DGDG occupied around the 1/5 and 1/7 of the total lipids in BJG, respectively. But they were about 1/4 and 1/6 in RG, which showed that these two components had more portion in RG than in BJG.
As shown in Figs. 8 and 9, the content of DGDG and MGDG was higher in Baijiguan than that in Rougui. DGDG (34:3), DGDG (36:6) and MGDG (36:6) are the main lipids in tea plants, their contents were higher in Rougui than those in Baijiguan before shading. After shading for one day, their contents in Baijiguan declined abruptly.
Lysophospholipid changes of Baijiguan and Rougui
Lysophospholipid which can be used as a signal molecule is produced by the partial hydrolysis of phospholipids. The contents of LPC and LPE in Baijiguan decreased dramatically to approximate 0.05 nmol/ mg DT after shading for one day. It is also showed that they decreased abruptly in BRL3 compared to BRL1 (Fig. 13B and C), while remained steady in Rougui (Fig. 13E and F). The LPG contents kept stable in Baijiguan and Rougui(Fig. 13A and D). At BC0, BC6, BS2, BS4 and BRL1, the contents of LPC in Baijiguan were significantly higher than that of Rougui. Like LPC, the LPE content of Baijiguan in BC0, BS4, BS6 and BRL3 was higher than that in Rougui in the same period.
Phospholipid changes of Baijiguan and Rougui
The content of PG, PC, PE, PI and PS in Baijiguan were significantly higher than those in Rougui. These lipids contents in Baijiguan declined obviously during the three treatments period, while did not show the same trend in Rougui. In the light resuming treatment, they increased remarkably instead of decrease. After shading for 1 day, the content of phospholipid in Baijiguan was decreased significantly. In addition, the content of phospholipid in the first day of recovery was significantly higher than that in the third day (Fig. 14A-F). But Rougui did not show the same trend in the this treatment. (Fig. 14G-L), and there was no significant change in the all treatments.
qRT-PCR analysis of lipid metabolism and chlorophyll degradation genes in Baijiguan
PLD, plc, DGK, MGD and DGD genes are some of the key genes in the lipid synthesis of the plant thylakoid membrane. In this study, the expression of these genes in the second leaves of Baijiguan treated with different light intensity was verified. The results showed that the expression of key genes of lipid synthesis after shading was generally higher than those expressed during the period of albinism and restoration of light, which indicated that membrane lipid synthesis was accelerated after shading (Fig. 15).
At the same time, we also verified the relative expression of chlorophyll degradation pathway. The results showed that the relative expression of chlorophyll degradation genes was generally lower after shading than that under normal light and light recovery period, indicating that chlorophyll degradation accelerated in albinism period (Fig. 16).