College of Life and Environment Sciences, Huangshan University, Huangshan 245041, China.
Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK.
Ann Bot. 2022 Mar 23;129(4):429-441. doi: 10.1093/aob/mcac002.
Many angiosperms can secrete both floral (FN) and extrafloral (EFN) nectar. However, much remains unclear about how EFN and FN differ in secretion, composition and ecological function, especially when both FN and EFN are secreted on flowers of the same species.
Hemerocallis citrina flowers secrete both FN and EFN. The FN and EFN traits including volume, presentation pattern and temporal rhythms of secretion were compared by field observation. Sugar and amino acid contents were analysed using regular biochemical methods, whereas the proteome was investigated by combined gel-based and gel-free approaches. Animal feeders on FN and EFN were investigated by field observation. Hemerocallis citrina plants were exposed by soil drenching to two systemic insecticides, acetamiprid and imidacloprid, and the concentration of these in FN and EFN was measured by ultra-high performance liquid chromatography coupled with mass spectrometry.
Hemerocallis citrina FN was concentrated and sucrose dominant, secreted in the mature flower tube and served as a reward for pollinators. Conversely, EFN was hexose rich, more dilute and less rich in sugar and amino acids. EFN was secreted on the outside of developing floral buds, and was likely to attract predatory animals for defence. EFN had fewer phenolics, but more pathogenesis-related components, such as chitinase and glucanase. A significantly different proteomic profile and enzymatic activities between FN and EFN suggest that they had different biosynthesis mechanisms. Both neonicotinoid insecticides examined became present in both nectar types soon after application, but in greater concentration within EFN; EFN also attracted a wider range of insect species than FN.
Hemerocallis citrina FN and EFN differed in production, composition and ecological function. The EFN pathway could be a significant way for neonicotinoids to enter the wild food chain, and must be considered when evaluating the risks to the environment of other systemic insecticides.
许多被子植物既能分泌花内蜜（FN），又能分泌花外蜜（EFN）。然而，关于 EFN 和 FN 在分泌、组成和生态功能方面的差异，仍有许多未解之谜，尤其是当同一物种的花朵同时分泌 FN 和 EFN 时。
萱草既能分泌 FN，也能分泌 EFN。通过野外观察比较 FN 和 EFN 的特征，包括分泌量、呈现模式和分泌的时间节律。采用常规生化方法分析糖和氨基酸含量，采用凝胶结合和无凝胶相结合的方法研究蛋白质组。通过野外观察研究 FN 和 EFN 上的动物取食者。通过土壤淋洗将两种系统杀虫剂，乙酰甲胺磷和吡虫啉暴露于萱草植株上，通过超高效液相色谱-质谱联用仪测定 FN 和 EFN 中的浓度。
萱草 FN 集中且以蔗糖为主，分泌于成熟花管中，作为传粉者的报酬。相反，EFN 富含己糖，较为稀释，糖和氨基酸含量较低。EFN 分泌于发育中的花蕾外部，可能吸引捕食性动物进行防御。EFN 中酚类物质较少，但富含几丁质酶和葡聚糖酶等与发病机制相关的成分。FN 和 EFN 之间的蛋白质组图谱和酶活性有显著差异，表明它们具有不同的生物合成机制。两种新烟碱类杀虫剂在施药后很快就出现在两种花蜜类型中，但在 EFN 中的浓度更高；EFN 还吸引了比 FN 更多种类的昆虫。
萱草 FN 和 EFN 在产生、组成和生态功能上存在差异。EFN 途径可能是新烟碱类杀虫剂进入野生食物链的重要途径，在评估其他系统杀虫剂对环境的风险时必须加以考虑。
