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Background: Hemerocallis citrina Baroni (daylily) is a horticultural ornamental plant and vegetable with various applications as a raw material in traditional Chinese medicine and as a flavouring agent. Daylily contains many functional substances and is rich in lecithin, which is mostly composed of glycerophospholipids. To study the comprehensive dynamic changes in glycerophospholipid during daylily flowering and the underlying signalling mechanisms, we performed comprehensive, time-resolved lipidomic and transcriptomic analyses of 'Datong Huanghua 6' daylily. Results: Labelling with PKH67 fluorescent antibodies clearly and effectively helped visualise lipid changes in daylily, while relative conductivity and malonaldehyde content detection revealed that the early stages of flowering were controllable processes; however, differences became non-significant after 18 h, indicating cellular damage. In addition, phospholipase D (PLD) and lipoxygenase (LOX) activities increased throughout the flowering process, suggesting that lipid hydrolysis and oxidation had intensified. Lipidomics identified 558 lipids that changed during flowering, with the most different lipids found 12 h before and 12 h after flowering. Transcriptome analysis identified 13 key functional genes and enzymes in the glycerophospholipid metabolic pathway. The two-way orthogonal partial least squares analysis showed that diacylglycerol diphosphate phosphatase correlated strongly and positively with phosphatidic acid (PA)(22:0/18:2), PA(34:2), PA(34:4), and diacylglycerol(18:2/21:0) but negatively with phospholipase C. In addition, ethanolamine phosphotransferase gene and phospholipid-N-methyltransferase gene correlated positively with phosphatidylethanolamine (PE)(16:0/18:2), PE(16:0/18:3), PE(33:2), and lysophosphatidylcholine (16:0) but negatively with PE(34:1). Conclusions: Overall, this study elucidated changes in the glycerophospholipid metabolism pathway during the daylily flowering process, as well as characteristic genes, thus providing a basis for future studies of glycerophospholipids and signal transduction in daylilies. [ABSTRACT FROM AUTHOR]

• Optimal extraction lecithin conditions: 90% ethanol, 1:20 material-solvent ratio, 30 min, 40°C • Highest lecithin content was obtained in the flower bud, specifically the stamen • Contents in freeze-dried flower buds higher than those in oven-dried/sun-dried buds • The best harvest period for daylily is between 18 h before flowering and bloom (0 h) • Lecithin synthesis in daylily was controlled by both the Kenndy de novo pathway and the triple sequential methylation pathway Hemerocallis citrina Baroni (daylily) is an important flower plant, consumed as food and used in traditional Chinese medicine. The daylily flower bud is rich in several functional substances, and lecithin is the most important among them. However, the optimum conditions for extracting lecithin from daylily flower buds are yet to be determined. The objective of this study was to examine the differences in the lecithin contents in daylily, identify the key enzymes and genes involved in lecithin synthesis, and establish the optimal conditions for lecithin extraction and detection by high-performance liquid chromatography. Initial treatment with acetone before ethanol extraction significantly increased the quantity of lecithin extracted compared with that extracted by direct ethanol extraction. The optimum lecithin extraction conditions were as follows: 90% ethanol concentration, 1:20 material-to-solvent ratio, 30 min extraction time, and 40°C extraction temperature. The highest lecithin content was obtained from the flower bud, specifically the stamen (3.49 mg/g). Additionally, the best harvest period for daylily flower buds with regards to lecithin content and nutritional quality was between 18 h before flowering and bloom (0 h). The lecithin content in freeze-dried daylily flower buds was higher than that in oven-dried and sun-dried flower buds. Among the varieties examined, Xiushan Huanghua (H0177) had the highest lecithin content (3.99 mg/g). Furthermore, the activity of phosphatidylethanolamine N-methyltransferase (PEAMT) was significantly higher than that of other enzymes involved in lecithin synthesis. Additionally, genes involved in lecithin synthesis were significantly expressed in the flower buds at different developmental stages. Overall, the findings of this study contribute to the understanding of lecithin synthesis in daylily. [ABSTRACT FROM AUTHOR]

• We studied development and senescence in daylily flowers over a 24 h period. • The loss of cell wall material and cohesion was associated with senescence. • Pectin-specific epitopes showed that the cell wall pectin had been remodeled. • Demethylesterification of the pectin was evident when the outer tepals opened. • The number of pectin side chains was greatly reduced during senescence. Ephemeral flower deaths occur within 24 h of flowering in the genus Hemerocallis. The senescence of plant organs is owing to the loss of cell wall cohesion. Pectin is the most structurally complex plant cell wall polysaccharide and has an important role in cell-to-cell adhesion. In this study, we used histological stains, immunolocalization and pectin characterization analyses to examine the dynamic changes in pectin in Hemerocallis citrina 'Datonghuanghua' tepals at eight stages (S1–S8). The pectin-specific antibodies JIM5 and JIM7, which hybridize to differently esterified regions of the homogalacturonan (HG) backbone, showed that demethylesterification of HG-type pectins was evident after the outer tepals had opened. Before flower opening, these two antibodies labelled tissue continuously across the cell wall, and the cells were round and tightly packed. The labeling of highly esterified epitopes recognized by JIM7 became deformed when the outer tepals opened. However, 12 h after blooming, low-and high-esterified epitope signals were disrupted near the vascular cylinder, and air space then appeared until these signals disappeared. labeling with the antibody LM5, which is specific for the (1 → 4)-β galactan side chains of rhamnogalacturonan-I, was disrupted near the vascular cylinder at the same stage. Moreover, the contents of neutral sugars in pectin analyses showed that galactose decreased significantly at 12 h after blooming. Three enzymes were involved in pectin remodeling at different developmental phases. The activities of pectin methylesterase continued to increase after the outer tepals opened and reached a significant peak at 12 h after blooming. The activities of polygalacturonase and pectate lyase also increased, but the difference was not significant. Our findings revealed that demethylesterification of HG-type pectins was evident after the outer tepals opened, and this remodeling greatly facilitated their degradation by pectic enzymes. The loss of cell wall material and cohesion that accompanied the activities of pectic enzymes was associated with senescence. Therefore, remodeling of the pectin in cell walls of the tepals is necessary for the occurrence of senescence. [ABSTRACT FROM AUTHOR]