The black nectar produced by Melianthus flowers is thought to serve as a visual attractant to bird pollinators, but the chemical identity and synthesis of the black pigment are unknown. A combination of analytical biochemistry, transcriptomics, proteomics, and enzyme assays was used to identify the pigment that gives Melianthus nectar its black color and how it is synthesized. Visual modeling of pollinators was also used to infer a potential function of the black coloration. High concentrations of ellagic acid and iron give the nectar its dark black color, which can be recapitulated through synthetic solutions containing only ellagic acid and iron(iii). The nectar also contains a peroxidase that oxidizes gallic acid to form ellagic acid. In vitro reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron(iii) fully recreate the black color of the nectar. Visual modeling indicates that the black color is highly conspicuous to avian pollinators within the context of the flower. Melianthus nectar contains a natural analog of iron-gall ink, which humans have used since at least medieval times. This pigment is derived from an ellagic acid-Fe complex synthesized in the nectar and is likely involved in the attraction of passerine pollinators endemic to southern Africa.
Bibliographical noteFunding Information:
The authors recognize the Center for Mass Spectrometry and Proteomics at the University of Minnesota and various supporting agencies, including the NSF for Major Research Instrumentation grants 9871237 and NSF‐DBI‐0215759 used to purchase the instruments described in this study. We thank the University of Minnesota Genomics Center for conducting RNA quality control, RNA‐seq library creation, next‐generation sequencing, and primary NGS data QC. We also thank Dr Rachel Vannette, Dino Sbardellati, Shawn Christensen, Jacob Francis, Tobias Mueller, Danielle Rutkoswki, and Ernesto Sandoval, all from the University of California Davis, for providing access to materials and additional research support, including extremely helpful sample collection and access to laboratory resources. Lastly, we thank Ruth Cozien of the Center for Functional Biodiversity, School of Life Sciences, University of Kwa‐Zulu Natal in South Africa for generously providing nectar samples collected from and and for helpful comments on the manuscript. This work was supported by grants from the US NSF to MH and CJC (IOS‐1339246); ECS‐R, MH, ADH and CJC (IOS‐2025297); and ADH (IOS‐1238812). RR was supported by a postdoctoral fellowship from the United States Department of Agriculture (2018‐67012‐28038). Melianthus M. pectinatus M. villosus
© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.
- ellagic acid
- gallic acid
- iron-gall ink
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't