Nectar and pollination drops: how different are they?

Abstract

Nectar and pollination drops contain sugars as the main components, but the total concentration and the relative proportions are different. They also contain amino acids, of which proline is frequently the most abundant. Proteomic studies have revealed the presence of common functional classes of proteins such as invertases and defence-related proteins in nectar (floral and extrafloral) and pollination drops. Invertases allow for dynamic rearrangement of sugar composition following secretion. Defence-related proteins provide protection from invasion by fungi and bacteria. Currently, only few species have been studied in any depth. The chemical composition of the pollination drop must be investigated in a larger number of species if eventual phylogenetic relationships are to be revealed. Much more information can be provided from further proteomic studies of both nectar and pollination drop that will contribute to the study of plant reproduction and evolution.

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

“…Fern nectaries produce watery, nutritionally poor secretions, whereas carbohydrate and amino acid concentrations of pollen drops from the four major lineages of gymnosperms-conifers, Ginkgo L., cycads, and gnetaleans-showed significantly more elevated nutritional levels, particularly in the two latter insectpollinated clades (Labandeira et al, 2007a). Nutritional levels in pollination drops of the four gymnosperm clades are similar to those of nectar from basal angiosperm lineages (Labandeira et al, 2007a;Wagner et al, 2007;Nepi et al, 2009). Lipid levels were not measured.…”

“…However, there are some beetle pollinators that do not directly feed on pollen but instead cover their bodies with unconsumed grains, some of which result in pollination (Donaldson, 1997). The dominance of a pollen-based reward in these gymnosperms contrasts with the dominance of fluid-based rewards that provide highly mobile, occasionally hovering insects with carbohydrate rewards to provide calories required for longer distances and powered flight (Haslett, 1989a;Wackers, 2002;Nepi et al, 2009).…”

“…Studies of the nutritional value of insect-consumed secretions occurring in present-day plants, including extranuptial nectary secretions in ferns, pollination drops in gymnosperms, and nectar and nectarlike secretions in basal angiosperms, suggest a third modification (Pacini et al, 2003;Nepi et al, 2009). Fern nectaries produce watery, nutritionally poor secretions, whereas carbohydrate and amino acid concentrations of pollen drops from the four major lineages of gymnosperms-conifers, Ginkgo L., cycads, and gnetaleans-showed significantly more elevated nutritional levels, particularly in the two latter insectpollinated clades (Labandeira et al, 2007a).…”

“…2, 9) are first known from Middle Jurassic Eurasian deposits that reveal siphonate proboscises either for nectaring, as in the case of the Nemestrinidae, or conceivably involved in bifunctional siphonate-stylate proboscises that would involve nectaring in males and joint nectaring and blood feeding in conspecific females, as in the pangioniine horseflies of the Tabanidae (Mostovski, 1998;Ren, 1998a;Mazzarolo & Amorim, 2000;Labandeira, 2005a). However, these mid Mesozoic clades are implicated in feeding only on surface fluids based on distinctive siphonate proboscises and associated mouthpart features (Mostovski, 1998;Ren, 1998b;Labandeira, 2005a), clumps of gymnospermous Classopollis pollen on their heads (Labandeira, 2005a; also see Nicholson, 1994), and high pollination-drop nutritive values from extant insectpollinated gymnosperms (Labandeira et al, 2007a;Nepi et al, 2009). Accordingly, these nectarivorous and palynophagous brachyceran flies initially targeted gymnospermous seed plants during the Middle Jurassic and evidently transferred their diets to angiosperms during their initial radiation of the Early Cretaceous.…”

“…This has been supplemented by the accumulation of new data and a more comprehensive understanding of plant-insect associations long before, during, and soon after the diversification of basal angiosperm lineages (Gorelick, 2001;Labandeira, 2005a, b;Labandeira et al, 2007a;Crepet, 2008;Nepi et al, 2009;Ollerton & Coulthard, 2009;Ren et al, 2009). Recent associational data build on the systematic placement of pollinating insect clades and their synchronicity or asynchronicity with emerging and radiating angiosperm lineages, and also contributes to a broader integration of more spatiotemporally diverse ecological data.…”