Plant Science, Ecology, Evolution, Behavior and Systematics, Insect Science
2
Scopus Publications
Scopus Publications
Structure and ultrastructure of nuptial and extranuptial nectaries explain secretion changes throughout flower lifetime and allow for multiple ecological interactions Hannelise Balduino, Priscila Tunes, Massimo Nepi, Elza Guimarães, Silvia Rodrigues Machado Aob Plants, 2025 Nectaries are specialized nectar-producing structures. Nectar traits affect animal behaviour and ecological and evolutionary processes, such as pollination and biotic defence. Previously, we found that there are differences in the characteristics of nuptial nectar (NN) and extranuptial nectar (ENN) and in the types of animals that visit each nectary in Amphilophium mansoanum (Bignoniaceae) flowers. We now hypothesize that nectar traits reflect the anatomical, histochemical, and subcellular characteristics of each nectary type. Using routine light microscopy, scanning electron microscopy, and transmission electron microscopy methods, we studied NN and ENN, respectively in young flower buds, pre-anthesis buds, and first- and second-day flowers. NN was a prominent annular disk; whereas, ENN was a concave, patelliform trichome. Only ENN contained alkaloids, while both nectaries contained starch grains, lipid droplets, proteins, terpenes, and phenolic compounds. Both nectaries showed subcellular organization consistent with hydrophilic and lipophilic secretion, the latter being predominant in second-day flowers. In NN, the subnectary parenchyma had phloem and amyloplasts until pre-anthesis. Starch grains decreased and tracheary elements were seen in newly opened flowers. ENN are not vascularized, with vascular bundles from the calyx approaching the base of the nectary. Starch grains were scarce and very small in the ENN secretory head cells. Fibrillary proteins were found only in NN and periplastidial reticulum was observed only in ENN. In NN, nectar secretion begins shortly before anthesis, being released through the raised stomata and the reticulate cuticle. In ENN, secretion extends from the young flower bud stage to senescent flowers, accumulating in small subcuticular spaces and being continuously released through the intact cuticle. Temporal differences in NN and ENN production, as well as in the structural characteristics and nectar release mechanisms between NN and ENN, may explain the differences in nectar characteristics of A. mansoanum.
To each their own! Nectar plasticity within a flower mediates distinct ecological interactions Hannelise de Kassia Balduino, Priscila Tunes, Emanuele Giordano, Massimo Guarnieri, Silvia Rodrigues Machado, et al. Aob Plants, 2023 Nuptial and extranuptial nectaries are involved in interactions with different animal functional groups. Nectar traits involved in pollination mutualisms are well known. However, we know little about those traits involved in other mutualisms, such as ant–plant interactions, especially when both types of nectaries are in the same plant organ, the flower. Here we investigated if when two types of nectaries are exploited by distinct functional groups of floral visitors, even being within the same plant organ, the nectar secreted presents distinct features that fit animal requirements. We compared nectar secretion dynamics, floral visitors and nectar chemical composition of both nuptial and extranuptial nectaries in natural populations of the liana Amphilophium mansoanum (Bignoniaceae). For that we characterized nectar sugar, amino acid and specialized metabolite composition by high-performance liquid chromatography. Nuptial nectaries were visited by three medium- and large-sized bee species and extranuptial nectaries were visited mainly by ants, but also by cockroaches, wasps and flies. Nuptial and extranuptial nectar differed regarding volume, concentration, milligrams of sugars per flower and secretion dynamics. Nuptial nectar was sucrose-dominated, with high amounts of γ-aminobutyric acid and β-aminobutyric acid and with theophylline-like alkaloid, which were all exclusive of nuptial nectar. Whereas extranuptial nectar was hexose-rich, had a richer and less variable amino acid chemical profile, with high amounts of serine and alanine amino acids and with higher amounts of the specialized metabolite tyramine. The nectar traits from nuptial and extranuptial nectaries differ in energy amount and nutritional value, as well as in neuroactive specialized metabolites. These differences seem to match floral visitors’ requirements, since they exclusively consume one of the two nectar types and may be exerting selective pressures on the composition of the respective resources of interest.
