Nectar: generation, regulation and ecological functions

Heil, Martin

doi:10.1016/j.tplants.2011.01.003

Cited by 422 publications

(471 citation statements)

References 95 publications

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“…For example, secondary nectar robbers (41) may use such capabilities to find and feed from punctured floral corollas. In this light, local humidity gradients could facilitate the location of extrafloral nectar present in small droplets on the plant surface by carnivorous arthropods (42).…”

Section: Discussionmentioning

confidence: 99%

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Arx

Goyret

Davidowitz

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

110

148

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Most research on plant-pollinator communication has focused on sensory and behavioral responses to relatively static cues. Floral rewards such as nectar, however, are dynamic, and foraging animals will increase their energetic profit if they can make use of floral cues that more accurately indicate nectar availability. Here we document such a cue-transient humidity gradients-using the night blooming flowers of Oenothera cespitosa (Onagraceae). The headspace of newly opened flowers reaches levels of about 4% above ambient relative humidity due to additive evapotranspirational water loss through petals and water-saturated air from the nectar tube. Floral humidity plumes differ from ambient levels only during the first 30 min after anthesis (before nectar is depleted in wild populations), whereas other floral traits (scent, shape, and color) persist for 12-24 h. Manipulative experiments indicated that floral humidity gradients are mechanistically linked to nectar volume and therefore contain information about energy rewards to floral visitors. Behavioral assays with Hyles lineata (Sphingidae) and artificial flowers with appropriate humidity gradients suggest that these hawkmoth pollinators distinguish between subtle differences in relative humidity when other floral cues are held constant. Moths consistently approached and probed flowers with elevated humidity over those with ambient humidity levels. Because floral humidity gradients are largely produced by the evaporation of nectar itself, they represent condition-informative cues that facilitate remote sensing of floral profitability by discriminating foragers. In a xeric environment, this level of honest communication should be adaptive when plant reproductive success is pollinator limited, due to intense competition for the attention of a specialized pollinator.pollination biology | honest signaling | floral display P lant-pollinator relationships-like all mutualisms-strike a tenuous balance between the conflicting interests of foraging animals and flowering plants (1, 2). For flowering plants, pollinator attraction through floral density, form, color, pattern, and odor is necessary but insufficient to ensure effective pollination. Ideally, pollinators should transfer pollen between conspecific plants in ways that result in favorable levels of outcrossing (3) and reduced pollen loss (4). Flowers commonly manipulate pollinator movement by varying quality or quantity of floral nectar. The offer of variable amounts of nectar (5, 6), toxic nectar (7, 8), or an empty promise of nectar elicit similar results: pollinators leave plants sooner, reducing for example geitonogamous inbreeding (if selfcompatible) or pollen discounting (if self-incompatible).The availability of floral rewards often coincides with floral display and pollinator activity on a gross temporal scale (i.e., hours) (9, 10). Nevertheless, most pollinators encounter rewardless ("empty") flowers on a finer temporal scale (i.e., minutes), often due to recent visitation by another animal. From the pollin...

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Section: Discussionmentioning

confidence: 99%

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Arx

Goyret

Davidowitz

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

110

148

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“…Van Die et al (1970) showed that following application of 14 C to the leaves of F. imperialis, radioactive label appeared in the floral nectar, indicating that nectar assimilates can be translocated directly from leaves. Because plastids present in the nectariferous parenchyma cells of F. meleagris did not display characteristic red fluorescence (it is possible that such pale red dispersed autofluorescence is affected by the presence of anthocyanins), they are probably not engaged in contributing assimilates to the nectar, as recorded for other plant species Vassiliev 2010;Heil 2011).…”

Section: Nectary Structurementioning

confidence: 94%

“…Plasmodesmata connect secretory cells and are particularly common in radial cell walls where they may facilitate additional transport of nectar along the symplast. These models of pre-nectar movement along the apoplast and/or symplast within secretory tissue, as well as the process of secretion, were proposed by several researchers (Gunning and Hughes 1976;Kronestedt-Robards and Robards 1991;Vassiliev 2010;Heil 2011). Some studies used radiolabelled sugars to follow the route taken by sugars within the nectary (Shuel 1961;Fahn and Rachmilevitz 1975;Meyberg and Kristen 1981;Sawidis et al 1989;Stpiczyńska 2003a, b;Ren et al 2007).…”

Section: Nectary Structurementioning

confidence: 99%

Secretion and composition of nectar and the structure of perigonal nectaries in Fritillaria meleagris L. (Liliaceae)

2012

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The structure of perigonal nectaries, nectar production and carbohydrate composition were compared at various stages in the lifespan of the flower of Fritillaria meleagris L. The six nectaries each occupied a groove that is located 2-4 mm above the tepal base. The average nectary measured 11.0 mm long and 1.0-1.2 mm wide. The structure of nectaries situated on both inner and outer tepal whorls was identical, and at anthesis they were equally accessible to potential pollinators. However, secretion from nectaries associated with inner tepals tended to exceed that produced by nectaries located on the outer tepals. On average, regardless of flower stage, one flower secreted 10.87 ± 12.98 mg of nectar (mean and SD; N = 182). The nectar concentration ranged between 3 and 75%, with average concentration of sugars exceeding 50%. Both nectar production and concentration were dependent on the stage of anthesis, with the highest scores being recorded during full anthesis (21.75 ± 16.08 mg; 70.5%, mass and concentration, respectively) and the lowest at the end of anthesis (1.32 ± 2.69 mg; 16.9%, mass and concentration, respectively). A decline in both mass of nectar secreted and nectar concentration during the final stage of anthesis indicates nectar resorption. Nectar was composed of sucrose, glucose and fructose in approx. equal quantities, and its composition did not change significantly during subsequent stages of flowering. The nectaries comprised a single-layered secretory epidermis and several layers of subepidermal parenchyma. The nectariferous cells did not accumulate starch during any of the investigated stages. The nectary was supplied with one large and several smaller vascular bundles comprising xylem and phloem. Transport of assimilates and nectar secretion by protoplasts of secretory cells (and probably also nectar resorption) were facilitated by cell wall ingrowths present on the tangential walls of epidermal cells and subepidermal parenchyma. Epidermal cells lacked stomata. Nectar passed across the cell wall and through the cuticle which was clearly perforated with pores.

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“…arabinose, galactose, mannose, gentiobiose, lactose, maltose, melibiose, trehalose, melezitose, raffinose and stachyose [5]. Besides sugars, nectar may contain glycosides, phenolic compounds, amino acids, reducing acids, fragrance compounds, lipids, proteins, alkaloids, antibiotics and vitamins [6,38,49]. Some of these minor nectar-components, such as phenolic compounds [10-11, 30, 32], amino acids [10-12, 24, 30-32, 43], antioxidant and reducing organic acids [12,20,31], sesquiterpenes, aromatic alcohols and aldehydes [44], as well as lipids [10,30,31] were reported in the floral nectar of certain Solanaceae species.…”

Section: Acta Biologica Hungarica 66 2015mentioning

confidence: 99%

Protein and alkaloid patterns of the floral nectar in some solanaceous species

Kerchner¹,

Darók²,

Bacskay³

et al. 2015

Acta Biologica Hungarica

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The family Solanaceae includes several melliferous plants, which tend to produce copious amounts of nectar. Floral nectar is a chemically complex aqueous solution, dominated by sugars, but minor components such as amino acids, proteins, flavonoids and alkaloids are present as well. This study aimed at analysing the protein and alkaloid profile of the nectar in seven solanaceous species. Proteins were examined with SDS-PAGE and alkaloids were analyzed with HPLC. The investigation of protein profile revealed significant differences in nectar-protein patterns not only between different plant genera, but also between the three Nicotiana species investigated. SDS-PAGE suggested the presence of several Nectarin proteins with antimicrobial activity in Nicotiana species. The nectar of all tobacco species contained the alkaloid nicotine, N. tabacum having the highest nicotine content. The nectar of Brugmansia suaveolens, Datura stramonium, Hyoscyamus niger and Lycium barbarum contained scopolamine, the highest content of which was measured in B. suaveolens. The alkaloid concentrations in the nectars of most solanaceous species investigated can cause deterrence in honeybees, and the nectar of N. rustica and N. tabacum can be considered toxic for honeybees.

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Nectar: generation, regulation and ecological functions

Cited by 422 publications

References 95 publications

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Secretion and composition of nectar and the structure of perigonal nectaries in Fritillaria meleagris L. (Liliaceae)

Protein and alkaloid patterns of the floral nectar in some solanaceous species

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