Project description:The black nectar of Melianthus flowers is thought to serve as a visual attractant to pollinators, but the chemical identity and synthesis of the black pigment are unknown. Here we report that the black nectar contains a natural analog of iron-gall ink, which humans have used since medieval times. Specifically, dark black nectar at anthesis contains high levels of ellagic acid and iron; synthetic solutions of ellagic acid and iron(III) recapitulate the black color of the nectar. Conversely, lightly colored nectars before and after anthesis contain significantly lower levels of ellagic acid and iron, but higher levels of gallic acid. We then explored the possibility of post-secretory synthesis of ellagic acid from gallic acid. Indeed, Melianthus nectar contains a peroxidase that oxidizes gallic acid to form ellagic acid. Reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron can fully recreate the black color of the nectar. Visual modeling indicates that the black color is both visible and conspicuous to birds within the context of the flower. In summary, the black nectar of Melianthus is derived from an ellagic acid-Fe complex analogous to iron-gall ink and is likely involved in the attraction of passerine bird pollinators.
Project description:Floral nectar proteins (nectarins) are mainly enzymes and play important roles in inhibiting microbial growth in nectar and tailoring nectar chemistry before or after secretory. Nectar proteomes are usually small, but only very few plant species have had their nectar proteomes thoroughly investigated. Nectarins from Nicotiana tabacum (NT) were separated using two-dimensional gel electrophoresis, and then analyzed using mass spectrometry. Glycoproteins were isolated from raw NT nectar, separated by SDS-PAGE, and identified by mass spectrometry. All eight identified nectarins and four invertase genes’ expression were analysed by qPCR. Sugars composition, total sugar concentration, protein content, polyphenol content and hydrogen peroxide content were compared at different time intervals in extracted nectar and nectar in situ after secretion. Totally, eight nectarins were detected in NT nectar in which only two are glycoproteins, beta-xylosidase and a protein with unknown function. All of the eight nectarin genes expression was not nectary-specific and not synchronous along with the nectary development. After secretion, NT nectar in flower tube changed from sucrose–rich to hexose-rich type even though no free invertase or its activity was detected in NT nectar. No sugar composition changes observed in extracted nectar after incubating at 30 ℃ up to 48 hours in plastic tubes. Our results indicate that nectar post-secretory changes could be a complex process and tissue closely contact with nectar might function in it.
Project description:Many angiosperms can secret at least two types of sugar-rich liquids, floral nectar (FN) and extrafloral nectar (EFN), by which plants can make use of the animal partner’s mobility for pollen transportation and attract predatory animals for indirect defense. Both FN and EFN contain considerable amount of proteins which play important roles in nectar biosynthesis process and protection. Hemerocallis citrina (HC) can secrete both FN and EFN on flower during the same developmental stage. Our objective was to compare the HC FN and EFN proteome to understand the difference between their biosynthesis and ecological function. FN was collected from adult HC flowers and concentrated by ultrafiltering. EFN was collected from young HC flower buds and concentrated by ultrafiltering. Proteins were digested with trypsin then analyzed by LC-MS/MS. HSPs are the main protein identified in HC FN but their function in floral nectar is still largely unknown. PR proteins are the main protein identified in HC EFN with antimicrobial activity. Our data provide a good characterization of a monocot nectar proteome. These data, may be useful in understanding the generation process and ecological function of floral and extrafloral nectar.