Comparing the contents, functions and neonicotinoid take-up between floral and extrafloral nectar within a single species (Hemerocallis citrina Baroni)

Hong-Xia Zhou, Richard I. Milne, Peng Cui, Wen Jing Gu, Meng Fang Hu, Xin Yue Liu, Yue-Qin Song, Jun Cao, Hong-Guang Zha

Research output: Contribution to journalArticlepeer-review

Abstract

Background and Aims
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.

Methods
Hemerocallis citrina flowers secrete both FN and EFN. 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 proteome was investigated by combined gel-based and gel-free approaches. FN and EFN animal feeders were investigated by field observation. H. citrina plants were exposed by soil drenching to two systemic insecticides, acetamiprid and imidacloprid, and the concentration of these in FN and EFN were measured by ultra-high performance liquid chromatography coupled with mass spectrometry.

Key Results
H. 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 less phenolics, but more pathogenesis-related components, such as chitinase and glucanase. 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.

Conclusions
H. 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.
Original languageEnglish
Article numbermcac002
JournalAnnals of Botany
DOIs
Publication statusPublished - 8 Jan 2022

Keywords

  • extrafloral nectar
  • floral nectar
  • Hemerocallis citrina Baroni
  • nectar proteome
  • systemic insecticides

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