Structure Of Floral Nectaries Research Articles

Diversity of petals in Berberidaceae: development, micromorphology, and structure of floral nectaries.

Petals are important floral organs that exhibit considerable morphological diversity in terms of colour, shape, and size. The varied morphologies of mature petals can be linked to developmental differences. The petals of Berberidaceae (a core group of Ranunculales) range from flat sheets to complex structures with nectaries, but studies on petal development and structural diversity in this group are lacking. Here, the petal development, structure, and micromorphology of seven Berberidaceae genera are characterized by microscopy to clarify the diversity of petals within this group. The results indicate that no common petal-stamen primordium exists, that petal development proceeds through five stages, and that the differentiation responsible for the diversity of the mature petals occurs during stage 4. Processes contributing to the morphological diversity of mature petals include edge thickening, gland formation, and spur formation. Nandina and Diphylleia lack nectaries. Gymnospermium has saccate nectaries, Caulophyllum has nectaries on the petal margin, Epimedium has spur nectaries, and Berberis and Mahonia have glands at the base of petals. Petal nectaries usually consist of a secretory epidermis, two to twenty layers of secretory parenchyma cells, and vascular tissues. Eleven distinct cell types were observed in the petal epidermis, three of which are secretory; papillose cells appear to be absent in Diphylleia, which shows relatively little micromorphological variation. The ancestors of Berberidaceae may have nectaries in thickened areas of their petals. The micromorphology and nectary structures of the petals in Ranunculales are also compared.

Structure of floral nectaries and female-biased nectar production in protandrous species Geranium macrorrhizum and Geranium phaeum.

Nectar is a major floral reward offered to pollinators by plants. In dichogamous plant species, differences in nectar production across sexual phases often occur, but both the male- and female-phase flowers have to attract pollinators to achieve effective pollination. Nectar-producing structures, i.e. floral nectaries, are a key component of floral organisation and architecture, and the knowledge of their structure and function contributes to better understanding of the plant-pollinator interactions. In the present study, we investigated the morphology and structure of nectaries and the nectar production pattern in two protandrous species Geranium macrorrhizum and G. phaeum. The flowers of the studied species have been shown to exhibit varied availability of nectar for insect visitors. Their nectaries differ in the shape, size and thickness. The other differences include the localisation of the stomatal field, the size and number of nectarostomata, the presence of non-glandular and glandular trichomes, the presence of tannin idioblasts, the mode of secretion and the occurrence of plastids functioning probably as autophagosomes and autolysosomes, whose presence in nectary cells has been described for the first time. The flowers of the studied species started nectar secretion in the non-receptive phase before pollen presentation and nectar was produced throughout both sexual phases. The nectar production was gender biased towards the female phase in the nectar amount, nectar sugar concentration and total sugar secreted in the nectar. We postulate that the nectar production patterns in G. phaeum and G. macrorrhizum might have evolved as a response to pollinators' pressure.

Comparative studies on structure of the floral nectaries and the abundance of nectar production of Prunus laurocerasus L.

There is very scanty information concerning the floral nectary structure and nectar secretion in Prunus laurocerasus L. Therefore, the aim of the study was to determine the micromorphology, anatomy and ultrastructure of nectaries; the abundance of nectar production; and the quantitative and qualitative composition of sugars contained in the nectar of two P. laurocerasus cultivars: ‘Schipkaensis’ and ‘Zabeliana’. The nectary structure was studied using light, fluorescence, scanning and transmission electron microscopy techniques. The nectar sugars were analysed with HPLC. The ‘Schipkaensis’ had longer inflorescences with a larger number of flowers and a longer perianth than ‘Zabeliana’. The micromorphological structure of the nectaries in ‘Schipkaensis’ exhibited denser (approx. 39%) and larger (approx. 50%) stomata and thicker (approx. 13%) cuticular striae forming wider bands (approx. 26%) than in ‘Zabeliana’. The results provide new data on the micromorphology, anatomy and ultrastructure of these floral nectaries. Nectary cuticle ornamentation as well as the size, type and density of stomata and stomatal complex topography can have a diagnostic value in Prunus. The nectar sugar weight indicates a significant apicultural value of the cherry laurel, especially in the case of ‘Schipkaensis’. Cherry laurel is an entomophilous species recommended for cultivation in nectariferous zones and insect pollinator refuges; however, climatic conditions eliminating the invasiveness of these plants should be considered.

Relationship between the morphological structure of floral nectaries and the formation, transport, and secretion of nectar in lychee

Key message The sugar in nectar secreted from the floral nectaries of lychee (Litchi chinensisSonn.) was composed of both the phloem sap and the starch synthesized by the nectariferous tissue itself. Sugar hydrolyzed from the starch and from the phloem might be transported to the endoplasmic reticulum (ER) and the Golgi cisternae, further transported via ER and Golgi vesicles, and eventually released to the spaces between the plasmalemma and cell wall by exocytosis. There was a specific sugar transport and secretory mechanism in the lychee floral nectary.

Flowering biology and structure of floral nectaries in Galanthus nivalis L.

In Poland <em>Galanthus nivalis</em> L. is partially protected. The flowers of this species are one of the first sources of nectar and pollen for insects from February to April. The aim of this study was to present the flowering biology as well as the topography, anatomical, and ultrastructural features of the floral nectary. The flower lifespan, the breeding system, and the mass of pollen and nectar produced by the flowers were determined. Examination of the nectary structure was performed using light, fluorescence, scanning and transmission electron microscopy. The flower of <em>G. nivalis</em> lives for about 30 days. The stamens and pistils mature simultaneously and during this time nectar is secreted. The anthers of one flower produced the large amount of pollen (4 mg). The breeding system of <em>G. nivalis</em> was found to be characterized by partial self-compatibility, outcrossing, and xenogamy. The nectary is located at the top of the inferior ovary. The nectary epidermal cells are characterized by striated cuticular ornamentation. Initially, the secreted nectar formed vesicle-like protuberances under the cuticle. The epidermal and parenchymal cells contain numerous plastids, mitochondria, dictyosomes, ER cisterns, and vesicles fused with the plasmalemma, which indicates granulocrine nectar secretion.

Floral nectar production and nectary structure of a bee‐pollinated shrub from Neotropical savanna

Biotic pollination is critical for tropical ecosystem functioning, and nectar plays an essential role as it represents the main trophic resource for pollinators. Nevertheless, little is known about the mechanisms that underlie its production, which is essential for understanding the basis of nectar-mediated interactions in ecological and evolutionary approaches. Therefore, this study explores the relationship between the nectar secretion pattern and nectary functional changes in Anemopaegma album, a bee-pollinated species. We analysed the pattern of nectar production under field conditions and investigated floral nectary structural changes in two different developmental stages using light, transmission and scanning electron microscopy. We measured 30.95 ± 23.02 μl (mean ± SD, n = 30) of nectar accumulated inside the nectar chamber (29.26 ± 3.48% sucrose equivalents) at the moment of flower opening. Nectar removal did not influence the pattern of floral nectar production in terms of volume or total sugar but reduced the concentration of the nectar produced during the first 24 h of anthesis. The nectary consisted of an epidermis, a nectary parenchyma and a subnectary parenchyma supplied only by phloem. Starch grains decreased in size and abundance from the subnectary parenchyma toward the epidermis. We observed the degradation of starch grains and incorporation of amyloplasts into vacuoles at the pre-anthesis stage as well as the transformation of amyloplasts into elaioplasts during anthesis. Nectar secretion was continuous during the A. album flower life span, which was related to the functional features of its floral nectary, especially the presence of starch stored in the parenchyma.

The structure of floral nectaries of some species of Vicia L. (Papilionaceae)

The subject of research were morphology and ultrastructure of floral nectaries of nine species of <i>Vicia</i>. The differences in their size and morphological structure were shown. Small, almost flat nectaries appeared in flowers of <i>Vicia tetrasperma</i> and <i>V. hirsuta</i>. Much better developed ones which had convexities with the shape of a protuberance, a half-ring or a half -ring with a ligulate outgrowth were observed in <i>V. silvatica</i>, <i>V. cracca</i>, <i>V. villosa</i>, <i>V. sativa</i> and <i>V. angustifolia</i>. Completely convex, annular nectaries with a ligulate outgrowth belonged to <i>V. sepium</i> and <i>V. grandiflora</i>. Small anatomical differences concerned mainly the structure and distribution of vascular bundles, whereas ultrastructure of secretory cells was very similar. Nectar got into the surface through the modified stomata situated on the top of nectaries' convexities.

Modified leaves with disk‐shaped nectaries of Macaranga sinensis (Euphorbiaceae) provide reward for pollinators

Nectar is the most common reward provided by animal-pollinated flowers. Diversity in position and structure of floral nectaries suggests that floral nectar production evolved repeatedly, but the evolutionary origins are not well known. Flowers of the genus Macaranga (Euphorbiaceae) are apetalous and lack floral nectar. Nevertheless, many Macaranga species possess disk-shaped nectaries on their leaves, sought by ants that defend plants from herbivory. In some Macaranga species, similar glands also occur on the bracteoles-modified leaves subtending the flowers. We investigated whether these glands on the bracteoles of M. sinensis are involved in pollination. • Flower visitors were captured, and body pollen was examined. The behavior of flower visitors on inflorescences was also observed. Sugar composition of the nectar from bracteoles and leaves was collected and analyzed using high-performance liquid chromatography. • Various bees and flies with body pollen visited both male and female inflorescences, feeding on nectar from the bracteoles and touching anthers and stigmas in the process. Sugar composition of nectar from the bracteoles and the leaves did not differ. • Macaranga sinensis was pollinated by insects foraging on the disk-shaped nectaries on bracteoles. The similar appearance, position, and sugar composition of nectar suggest that disk-shaped nectaries on bracteoles and leaves are homologous and that nectaries on leaves were recruited to inflorescences to serve floral function in M. sinensis. Having protective mutualism with ants has likely opened an unusual route for the evolution of floral nectar in otherwise non-nectar-producing flowers of M. sinensis.

Structure of floral nectaries, nectar production and sugar composition in nectar of 7 species of Vicia L. Fabaceae

Nectaries of investigated species of <em>Vicia</em> were ranked into 3 morphological types: automorphic (<em>V. sepium</em> L.), transitoric (<em>V. angustifolia</em> L., <em>V. sativa</em> L., <em>V. villosa</em> Roth, <em>V. cracca</em> L.) and flat, epimorphic (<em>V. hirsuta</em> (L.) S. F. Gray and <em>V. tetrasperma</em> (L.) Schreb.). The best nectaring was connected with well defined nectary structure, and moreover quantity of nectar was correlated with nectary size but was not depended on number of secretory stomata. Sucrose dominated in the nectar of 6 species of vetches, the exception was balanced nectar of <em>V. tetrasperma</em>.

Micromorphology of nectaries of Rhododendron catawbiense Michx. at different flower development stages

The analysis of the structure of fl oral nectaries of <i>Rhododendron catawbiense</i> Michx. was performed using stereoscopic, light and scanning electron microscopy. Nectaries were sampled at different development stages: closed bud, budburst and full bloom. The nectary gland exhibits clear ribbings corresponding to fi ve small ribs of the ovary. In the top part of the gland, unicellular and multicellular non-glandular trichomes occur in great density. The upper surface of the nectary differs from its lateral surface by a stronger degree of cuticle development. Stomata are evenly distributed on the upper surface and in the higher regions of the lateral wall. The cuticle forms clear striae on the surface of stomatal cells. Stomata at different development stages were observed, as well as the beginning of nectar secretion which takes places already in the closed bud.

Flowering biology and nectary structure of Melissa officinalis L.

The present study on lemon balm (<i>Melissa officinalis</i> L.) covered flowering biology, monitoring of pollinating insects and floral nectary structure. The micromorphology of epidermal cells of the nectary was investigated using scanning electron microscopy. The nectariferous tissues were observed using light microscopy based on semi-thin sections. Lemon balm flowered from the second decade of June until September. Buds opened from early morning hours until noon. Flowers lived for 24 hours, on the average. Their primary pollinator was the honey bee. The beginning of nectar secretion was found to be at the bud swell stage. The automorphic nectary forms a disc with four protrusions at the base of the nectary. Three smaller ones and one larger than the other ones were distinguished among them. No stomata were found on the lower protuberances, whereas on the highest part anomocytic stomata were present, the number of which was 15. The stomata exhibited different development stages and they were situated above other epidermal cells. In their outline, they were ellipsoidally shaped (18 × 23 µm) and they had average-sized cuticular ledges. They produced a smooth cuticle and wax granules. In cross section, the nectary tissues were composed of a singlelayered epidermis and 9 - 11 layers of the nectary parenchyma. Their thickness was 198 µm. In longitudinal section, the height of the nectary was within a range of 354 - 404 µm. The epidermal cells produced thin outer cell walls. Some of them were completely filled with strongly stained cytoplasm, whereas others showed a high degree of vacuolisation. But the nectary parenchyma cells were marked by poorly stained cytoplasm, a large nucleus and vacuolisation of varying degree.

Diversity of the floral nectaries surface of four Crataegus L. species

The performed studies focused on the surface structure of floral nectaries of four species from the following genus: <i>C. coccinea</i> L. , <i>C. crus-galli</i> L., <i>C. curvisepala</i> Lindm and <i>C. prunifolia</i> (Poiret) Pers. The observations of the epidermis area were made in a scanning electron microscope (SEM). A nectary appears to be shaped like a slightly curved disk situated between the pistil style and the basal part of the stamens filaments. The nectary area of the studied species differed substantially as regards the cuticle sculpture and stomata number. The nectary secretion in <i>Crataegus</i> flowers proceeds through the stomata located below a level of the other epidermis cells, in the deep indents of the secretory tissue. The highest stomata number in 1 mm<sup>2</sup> nectary epidermis was recorded in <i>C. crus-galli</i>, <i>C. coccinea</i>, <i>C. prunifolia</i> and finally, <i>C. curvisepala</i>. Analyzing the nectary cuticular structure in respect of its increasing complexity (absence or presence of stripes), the investigated taxons can be ordered as following: <i>Crataegus curvisepala</i>, <i>C. coccinea</i>, <i>C. crus-galli</i> and <i>C. prunifolia</i>.

Pollen and ovule production, floral nectary structure, and nectar secretion dynamics in tristylous Lythrum salicaria L.

Lythrum salicaria L. (Lythraceae) is tristylous, each plant forming one of three floral morphs that differ in reciprocal placement of the stigma and two sets of anthers. Several reproductive traits were compared quantitatively among these morphs. Although mean pollen viability (≥93%) and total pollen per mature, indehiscent anther within a staminal level (mean CV = 11%) were constant, the patterns of mean pollen production per anther were complex, being significantly lowest in long stamens (1,490 grains) of the short-styled morph, but highest in intermediate stamens (3,590) of the long-styled morph. Overall, pollen production was greatest (38,200) in long-styled flowers and least (22,000) in short-styled ones. On the contrary, ovule quantities per ovary (mean 107) were similar among floral morphs; thus, pollen-to-ovule ratios spanned 192 (short-styled morph) to 364 (long-styled morph), relatively low values for a strictly xenogamous species. Each morph had a recessed annular nectary of similar dimensions encircling the ovary base, with equal numbers of modified stomata distributed uniformly on the nectary surface. Most stomata were solitary (94%), whereas 5% occurred in pairs and 1% of stomatal units had just one guard cell. During nectar secretion, about 16% of pores were closed plus 28% of pores were fully occluded. Similarly, nectar volumes and solute concentrations, peak rates of nectar secretion (mean 72–79 μg sugar h−1) at early afternoon, and the nectar’s sucrose prevalence [S/(G + F) ≥4.3] were not significantly different among morphs. Based on these similarities in nectary structure and nectar-secretion dynamics, traits rarely studied in tristylous species, the preferential visitation of any particular floral morph of L. salicaria during nectar foraging by insects is unlikely. Indeed, lack of discrimination among morphs by potential pollinators may be a key tenet of successful sexual reproduction in tristylous species.

Floral nectary structure, nectar production, and carbohydrate composition in theLiliumAsiatic hybrid ‘Trésor’

Floral nectary structure, nectar production, and carbohydrate composition were compared from petals (“inner tepals”) and sepals (“outer tepals”) of Lilium Asiatic hybrid ‘Trésor’ (Liliaceae). The six nectaries each occupied a narrow furrow bordered by two convergent ridges extending adaxially from the petal and sepal base. Each sepal nectary furrow was shorter and more concealed. In both nectary types, many vascular bundles comprising xylem and phloem supplied 5.5–8 layers of nectariferous parenchyma cells below the epidermis, which lacked stomata. Transmission electron microscopy of sepal nectaries demonstrated that parts of the outer epidermal wall adhered to an intact but uplifted cuticle in nectar-secreting flowers. Both apoplastic and symplastic routes were continuous from the vascular bundles to the nectary epidermis. Starch breakdown from amyloplasts throughout the nectary likely augmented nectar production. Nectar solute concentration from another Asiatic hybrid, ‘Orange Pixie’, was also significantly higher in petals. In ‘Trésor’, significantly more nectar was available from sepals, possibly reflecting reduced evaporation from multiple nectar droplets within the covered nectary furrow. However, for both hybrids, the same quantity of nectar sugar was produced by petals and sepals. Nectar composition from petals and sepals also was alike, in ‘Orange Pixie’ averaging 67/19/14 (= sucrose/fructose/glucose) and 59/25/17, respectively, and in ‘Trésor’ averaging 68/23/10 and 62/27/12, respectively.

Influence of elevated CO2 and ultraviolet-B radiation levels on floral nectar production: a nectary-morphological perspective

Investigations of the effects of two global events – elevated CO2 levels and enhanced ultraviolet-B (UV-B) radiation – on floral nectar production are reviewed from twelve dicotyledonous families. Furthermore, to allow comparisons between nectary morphology and nectar production in treated plants of these fifteen species, new data on floral nectary structure are provided for Malcolmia maritima (L.) R. Br. (Brassicaceae) and Scabiosa columbaria L. (Dipsacaceae). All but the last taxon possessed mesenchymatic floral nectaries with surface stomata. Few clear relationships existed between nectary morphology and various physiological responses to CO2 or UV-B enrichment, indicating that species responded notwithstanding nectary structure itself. Overall, nectar-solute concentration was least affected by elevated CO2 or UV-B radiation; consequently, changes in nectar volume were responsible for differences in nectar-sugar production per flower. Three species of Fabaceae experienced no change in floral nectar production upon exposure to elevated CO2. To date, no study of enhanced UV-B radiation reported a consistent reduction in floral nectar production; three species of Brassicaceae responded differently, but various levels of ozone depletion were simulated. Experimentation with more taxa – including those possessing nectary types such as septal (gynopleural) nectaries (e.g. many monocotyledons) or aggregations of glandular trichomes – and expanding such physiological studies to species possessing extrafloral nectaries, are recommended.

Characteristics of floral nectaries and nectar in two species of Crataegus (Rosaceae)

The structure of floral nectaries of Crataegus coccinea and C. crus-galli was examined using light and scanning electron microscopy. The radial length of the floral nectary, measured from longitudinal sections of flowers, was 30% larger in C. crus-galli than in C. coccinea. For both Crataegus species the glandular tissue thickness was similar – approx. 400 μm. Also, the number of stomata per mm2 of nectary surface in C. crus-galli was much higher (by 43%) than for C. coccinea. Stomata were situated in deep hollows. For both taxa the period of nectar secretion was 4 days. The mean quantity of total sugar in nectar per 10 flowers of C. crus-galli and C. coccinea was 3.87 mg and 0.33 mg, respectively.

Floral nectary structure and nectar chemical composition of some species from Robinson Crusoe Island (Chile)

Floral nectary structure and nectar composition of 12 species, including 11 endemics, are reported from Robinson Crusoe Island (Juan Fernández Archipelago, Chile). These species are mostly hummingbird pollinated. Nectary morphology follows the general pattern within each of the families, suggesting it is an ancestral feature. The mean nectar concentration (± SD) as a percentage of weight (weight/total weight of solution) was 28.3 ± 20.7. Sucrose, fructose, and glucose were identified in most samples. In Nicotiana cordifolia, an unknown monosaccharide was also detected. When more than one sample per species was examined, there was usually variability in sugar ratios. Statistical tests indicated that population size does not influence this variability. However, there were differences when the pollinator type was compared, with a trend of a higher sucrose proportion and a lower coefficient of variation of sucrose in the species pollinated by hummingbirds. This would indicate a specialization in the nectar composition of the hummingbird-pollinated species. Cuminia eriantha, N. cordifolia, and Rhaphithamnus venustus also possess amino acids in their nectar. In the non-hummingbird-pollinated species, the presence of nectaries and nectar serves as an indication of the ancestral pollination system of the first colonizers rather than the current condition, which is wind pollination or self-compatibility for most of the species. Thus, the presence of nectar in flowers does not necessarily indicate extant biotic pollination.Key words: angiosperms, Robinson Crusoe Island, nectary structure, nectar sugar composition, sugar concentration, hummingbird pollination.

Floral nectary structure and nectar chemical composition of some species from Robinson Crusoe Island (Chile)

Floral nectary structure and nectar composition of 12 species, including 11 endemics, are reported from Robinson Crusoe Island (Juan Fernandez Archipelago, Chile). These species are mostly hummingbird pollinated. Nectary morphology follows the general pattern within each of the families, suggesting it is an ancestral feature. The mean nectar concentration (± SD) as a percentage of weight (weight/total weight of solution) was 28.3 ± 20.7. Sucrose, fructose, and glucose were identified in most samples. In Nicotiana cordifolia, an unknown monosaccharide was also detected. When more than one sample per species was examined, there was usually variability in sugar ratios. Statistical tests indicated that population size does not influence this variability. However, there were differences when the pollinator type was compared, with a trend of a higher sucrose proportion and a lower coefficient of variation of sucrose in the species pollinated by hummingbirds. This would indicate a specialization in the nectar co...

Floral Nectary Structure and Nectar Composition in Eccremocarpus scaber (Bignoniaceae), a Hummingbird-Pollinated Plant of Central Chile

Surface features, anatomy, and ultrastructure of the floral nectary of Eccremocarpus scaber (Bignoniaceae), pollinated predominantly by the largest-known hummingbird (Patagona gigas gigas), were studied together with nectar sugar content and secretion rate. The annular disk nectary comprises epidermis, secretory and ground parenchyma with intercellular spaces, and branched vascular bundles terminating in the secretory parenchyma where only phloem is found. Amyloplasts and vacuoles increase in size throughout development, the latter becoming sites of organelle degradation. Transferlike cells in nectary phloem and P-proteinlike fibrillar material in phloem parenchyma were observed. Flowers produced around 32 μl of nectar (mostly after anthesis) with 11 mg of sugar composed of fructose, glucose, sucrose, and maltose in a ratio of 0.34:0.32:0.17:0.17. Morphological studies as well as the presence of maltose and glucose in nectar suggest storage of the originally phloem-derived sugars as starch with its subsequent hydrolysis. The low sucrose/hexose ratio (0.25) and high nectary secretion force (nectar per flower biomass) observed places E. scaber close to large-bodied bat-pollinated plants. A hypothesis based on nectar origin and nectar secretion is advanced to explain pollinator-correlated variation in sucrose/hexose ratio.

Floral nectary structure and nectar composition in Eccremocarpus scaber (Bignoniaceae), a hummingbird‐pollinated plant of central Chile

Surface features, anatomy, and ultrastructure of the floral nectary of Eccremocarpus scaber (Bignoniaceae), pollinated predominantly by the largest‐known hummingbird (Patagona gigas gigas), were studied together with nectar sugar content and secretion rate. The annular disk nectary comprises epidermis, secretory and ground parenchyma with intercellular spaces, and branched vascular bundles terminating in the secretory parenchyma where only phloem is found. Amyloplasts and vacuoles increase in size throughout development, the latter becoming sites of organelle degradation. Transferlike cells in nectary phloem and P‐proteinlike fibrillar material in phloem parenchyma were observed. Flowers produced around 32 μl of nectar (mostly after anthesis) with 11 mg of sugar composed of fructose, glucose, sucrose, and maltose in a ratio of 0.34:0.32:0.17:0.17. Morphological studies as well as the presence of maltose and glucose in nectar suggest storage of the originally phloem‐derived sugars as starch with its subsequent hydrolysis. The low sucrose/hexose ratio (0.25) and high nectary secretion force (nectar per flower biomass) observed places E. scaber close to large‐bodied bat‐pollinated plants. A hypothesis based on nectar origin and nectar secretion is advanced to explain pollinator‐correlated variation in sucrose/hexose ratio.