Nectary Structure Research Articles

Micromorphology of the epidermis of the floral nectary of Rhododendron japonicum (A. Gray) J. V. Suringar ex E.H. Wilson.

The conducted study related to the structure of the floral nectaries of <i>Rhododendron japonicum</i> (A. Gray) J. V. Suringar ex E. H. Wilson. The structure of the secretory epidermis of the nectaries was analysed by using scanning electron microscopy (SEM). <i>Rhododendron japonicum</i> develops the superior pistil with a 5-loculed ovary equipped in five ribs. The nectary gland is located in the lower part of the ovary. In the nectary regions located on the extension of the ribs of the ovary, stomata were very numerous. In the upper part of the nectary, stomata were arranged individually or in small clusters, whereas at its half- -height they formed stomatal areas. The stomata were at different growth stages. They were arranged in different directions. The stomata developed on the nectary surface according to the mosaic pattern. The stomata from the lower situated part of the nectary had a different structure than those occurring in the upper half of the nectary. The stomata in the nectaries of <i>Rh. japonicum</i> belong to the actinocytic type. The cuticle layer in the upper part of the nectary was better developed and had a characteristic sculpture, whereas in the lower part it was smooth.

Anatomy and ultrastructure of floral nectaries of Asphodelus aestivus Brot. (Asphodelaceae)

The structure of septal nectaries in <i>Asphodelus aestivus</i> flowers was investigated by using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (EM). It was found that the outlets of the three parts of the nectary were situated on the ovary surface at 2/3 of its height and had the shape of elongated openings. The nectariferous tissue was in the septa of the lower part of the ovary. The secretory tissue cells formed 1-3 layers surrounding the nectary slits. They contained thin cell walls with the cuticle layer from the slit side, large cell nuclei, numerous mitochondria and plastids characterised by various shapes. In plastids, small starch grains occurred sporadically. At the beginning of anthesis, the cells were poorly vacuolized. ER cisternae and secretory vesicles were located near the outer cell wall. Fibrous substance was present in the nectary slits. In the subglandular tissue, numerous starch grains occurred at the beginning of anthesis. In this zone, cells containing raphides and xylem elements were observed. Based on the ultrastructure of the nectary it can be stated that granulocrine nectar secretion occurs in <i>A. aestivus</i>.

The location of nectaries and nectar secretion in the flowers of Allium giganteum Regel

In the flowers of <i>Allium</i> there are found septal nectaries; in particular species, their outlet can be located in different parts of the ovary. The inflorescences of these plants are a rich source of nectar for insects. The location and structure of septal nectaries in the flowers of <i>Allium giganteum</i> Regel were investigated. Light and scanning electron microscopy was used. The septal nectaries were found to be located in the lower part of the ovary and in the gynophore on which the ovary is borne. Nectar is secreted into the nectary slits from which it flows through the ducts to three openings located in the upper part of the gynophore, from whence it gets outside in the vicinity of the expanded parts of the filaments. Sugar concentration in the nectar of <i>A. giganteum</i> averaged 54.5%, while sugar weight per flower was determined to be 0.36 mg. When converted into sugar weight per inflorescence, numbering more than 2,000 flowers, it was 771.7 mg.

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.

"Sweet but dangerous": nectaries in carnivorous plants

In carnivorous plants, two types of nectaries occur: extra-floral nectaries, generally associated with prey luring, and floral ones associated with pollination. Nectar produced by extra-floral nectaries not only attracts prey but may also be involved in trapping prey and plays a role in myrmecophily. The diversity of nectary structure in carnivorous plants reflects complicated evolutionary routes in this unique ecological group.

The comparison of nectaries structure of some varieties of ornamental apple

The study of floral nectary structures of thirteen ornamental apple cultivars examined using light microscope (MS) and scanning electron microscope (SEM) was performed. It was found that nectary glands in the selected cultivars were located in the upper part of the flower receptacle, between the ovary of the pistil and the base of stamen filaments, and they generally belonged to the epimorphic or transitoric type. The nectary surface area, its thickness, the number of glandular tissue layers, the height of epidermal cells of the nectary and the thickness of the outer wall of the epidermis, together with the cuticle, were determined by light microscope. By using SEM, the structure of the surface of nectaries in four ornamental apple cultivars was observed. The epidermis of the upper part of the nectaries was composed of elongated cells of which outer cell wall was covered with a striated cuticle. The remaining part of the nectary was characterised by cells of similar arrangement and shape, but their surface was marked by a thinner and smoother layer of cuticle. Closed or opened stomata were generally situated at the level of the epidermal cells. Their pores were often filled with granular or plate-shaped structures.

Nectary structure in Symphyglossum sanguineum (Rchb.f. ) Schltr. (Orchidaceae)

Ornithophily occurs in a great number of orchid species but despite this, researchers have largely neglected to investigate their nectaries. The aim of this study is to describe the nectary structure of <i>Symphyglossum sanguineum</i>, a species presumed to be pollinated by hummingbirds. The nectary is located at the free margins of auricles, which form a channel for the passage of nectar. The nectary, which consists of a single-layered epidermis and 2-3 layers of subepidermal cells, is supplied by collateral, vascular bundles. The nectary cells of <i>S. sanguineum</i>, like those of other ornithophilous orchids, have thick cellulose cell walls. A remarkable feature of these nectary cells is the dissolution of the middle lamella and the subsequent separation of epidermal cells. It is possible that this latter process facilitates the flow of the nectar to the nectary surface. The cuticle covering the nectary epidermis has micro-channels, but unlike the other species of ornithophilous orchids studied to date, it neither becomes disrupted nor detached from the epidermal cells. Abundant mitochondria, lipid droplets and smooth endoplasmic reticulum (SER) with an osmiophilic material are present in the cytoplasm of nectary cells. Some plastids with few lamellae contain numerous vesicles and osmiophillic globules whereas others accumulate starch. SER lamellae are often closely associated with plastids and the contents of the former organelles closely resemble osmiophillic globules. Secretory vesicles are common, especially near the outer, tangential wall indicating that granulocrine secretion possibly occurs in <i>S. sanguineum</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.

Flower nectary structure in Cornus alba L.

The structure of the floral nectaries of Cornus alba was studied using light microscopy as well as scanning and transmission electron microscopy. It was found that the nectary gland of white dogwood had the shape of a fleshy ring surrounding the base of the style of the inferior ovary. Nectar secretion occurs through slightly depressed stomata, evenly distributed in the epidermis of the nectary. The nectariferous tissue is composed of over a dozen layers of heterogeneously structured cells. Between groups of cells with a typical structure, characteristic for the secretory tissue, cells occur with degenerated content and a high degree of vacuolization. In the area of the nectary gland cells, no vascular tissue elements were observed. The nectary was irrigated by the vasculature of the flower receptacle.

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.

Comparative Floral Structure and Systematics of Fouquieriaceae and Polemoniaceae (Ericales)

Floral morphology, anatomy, and histology are comparatively studied in Fouquieriaceae and Polemoniaceae, and previous studies are reviewed. In recent molecular phylogenetic analyses, the two families form a strongly supported clade within the asterid order Ericales, while they were generally placed far from each other in premolecular classifications. This study documents unexpectedly diverse floral features for Polemoniaceae, including various corolla aestivation patterns, different types of anther attachment and anther morphology, as well as two types of nectary structure. Prominent features shared by the two families include determinate‐terminal inflorescences, hyaline sepal margins, similar patterns of floral vasculature, late sympetalous corolla development, similar degrees of sympetaly, sterile connective protrusions, short thecal septa, endothecium‐like cells in the connective, trimery in the gynoecium, a stylar canal, parietal, and axile and placentation in the same ovary, similar patterns of ovule arrangement and ovule orientation, distally curved micropylar canals, mesophyll‐type nectaries with stomata, winged seeds, and seed coat epidermal cells with helical or annular wall thickenings. Several of these features represent potential synapomorphies for the clade with Fouquieriaceae and Polemoniaceae. In addition, potential synapomorphies are also identified for the individual families. While the results of this investigation further support the close relationship of Polemoniaceae and Fouquieriaceae, they also emphasize that it is necessary to abandon preconceptions about the “systematic importance” of certain characters that turn out to be more homoplasious than previously thought.

Morphology of nectaries and biology of nectar production in the distylous species Fagopyrum esculentum.

The mechanisms of floral nectar production in buckwheat (Fagopyrum esculentum, Polygonaceae), a distylous pseudo-cereal, have received relatively little attention, prompting an investigation of the factors that regulate this process. The aim was to perform a refined study of the structures that secrete nectar and of the internal and external parameters influencing nectar volumes and sugar concentrations. In order to control environmental parameters, plants were cultivated in growth rooms under controlled conditions. The structure of nectaries was studied based on histological sections from flowers and flower buds. Nectar was extracted using glass micropipettes and the sugar concentration was measured with a hand refractometer. Sugar concentration in the phloem sap was measured using the anthrone method. To test the influence of photosynthesis on nectar production, different light and defoliation treatments were applied. Unicellular trichomes were located in the epidermis at the ventral part of eight nectary glands situated on the flower receptacle alternately with stamens. Vascular bundles consisting of both phloem and xylem were identified at the boundary between a multilayered nectary parenchyma and a sub-nectary parenchyma with chloroplasts. A higher volume of nectar in thrum morphs was observed. No other difference was found in morphology or in sugar supply to inflorescences between morphs. Nectar secretion was strongly influenced by plant age and inflorescence position. Nectar volumes were higher in the upper inflorescences and during the flowering peak. Light had a dual role, (1) acting directly on reproductive structures to trigger flower opening, which conditions nectar secretion, and (2) stimulating photosynthetic activity, which regulates nectar accumulation in open flowers. In buckwheat, nectar is secreted by trichomes and probably proceeds, at least in part, from phloem sap. Nectar secretion is strongly influenced by floral morph type, plant age, inflorescence position and light.

Morphology and anatomy of the Cordia trichotoma (Vell.) Arrab. ex I. M. Johnst diaspore (Boraginaceae)

This study analyzed the morphology and anatomy of the Cordia trichotoma (Vell.) Arrab. ex I. M. Johnst diaspore. The objectives were: the structural analysis of the calyx and corolla that persisted in the ripe fruit and acted in the anemocoric dispersion process; the vascularization of the gynoecium for better understanding of the carpel/locule number of the ovary; nectary structure; and the anatomical analysis of the developmental pericarp and seed for better definition of the fruit type. The results showed that the perianth had aerenchyma and the ovary was 2- 4- locule forming endothelium and false septum. The fruit was drupoid nuculanium and the seed was exotestal.

Floral Structure and Dynamics of Nectar Production inEchinacea pallidavar.angustifolia(Asteraceae)

The reproductive structure of the disk florets of Echinacea pallida var. angustifolia (Asteraceae) in relation to insect pollination was investigated using light, fluorescence, and scanning electron microscopy. The study of this self‐incompatible species emphasized pollen production, pollen‐stigma interactions, transmitting tissue, and vasculature within the style. Nectary structure and nectar production dynamics were also examined. Produced in the fused anther tubes, the trinucleate pollen with yellow pollenkitt was plentiful per floret, yielding a pollen:ovule ratio of 24,130. Encircling the style base at the ovary summit, the floral nectary possessed modified stomata whose pores, as well as nonstomatal gaps in the epidermis, provided apoplastic pathways for nectar escape and reabsorption. Phloem alone supplied the gland interior, the sieve element–companion cell complexes reaching up to the nectary epidermis. Nectar was hexose dominant, its volume and nectar‐sugar quantity per floret peaking on the aft...

Morphological comparison of floral nectaries in Musaceae, with refer-ence to its pollinators

The floral nectaries of three species of Musaceae s. s. representing the genera Musa, Ensete and Musella were comparatively investigated. Our observations revealed that nectaries of these three genera belonged to the interlocular septal type. In female flowers, nectaries were limited to the upper part of the ovaries above the locules, while in male flowers (with aborted ovaries) nectaries entirely occupied the aborted ovaries. A transection of nectary ducts suggested a complex and highly proliferated labyrinthine structure. The three species shared a few common features in the palisade-like epithelial cells, vascular supplies, and nectary openings. However, they showed some differences in longitudinal section and transectinal outline. The nectaries of Ensete glaucum had the highest starch content, and those of Musa basjoo and E. glaucum had fibrillar material presented in nectar ducts. Pollination syndromes among the three species showed high diversity, while inflorescence and flower characters (such as pendant or erect inflorescences, bract color, nectar volume and production over time, etc.) and pollination patterns were highly correlated. There were no strong correlations between nectary structures and pollinator behavior, although gelatinous or watery nectar was associated with the foraging preference of pollinators.

Flowering phenology, nectary structure and breeding system in Corymborkis flava (Spiranthoideae:Tropidieae), a terrestrial orchid from a Neotropical forest

Flowering phenology, breeding system and nectary structure of Corymborkis flava (Sw.) Kuntze were studied in a fragment of the Atlantic Forest in south-eastern Brazil. The flowering period extended from March (end of rainy season) to early June and seed dispersal occurred from June to September (dry season). Flowering peak occurred mainly in April, with up to 34 open flowers per plant being observed. The yellow, odourless and tubular flowers lasted ~7.8 days. The flowers present a perigonal nectary located in the basal lateral parts of the labellum; this is the first report on the nectary location and characterisation in the Tropidieae tribe. At the pre-anthesis stage, cells of both secretory parenchyma and epidermis of the nectary are filled with compound amyloplasts. However, starch grains were not observed in these tissues in senescent flowers, indicating that these starch grains are hydrolysed and used as source of sugars for nectar production. The nectar accumulates between the cuticle and the outer periclinal wall of the epidermal cells before flowing out into the nectar chamber. C. flava is a self-compatible species and spontaneous self-pollination does not occur because of hercogamy. The high pollinia removal (0.80) and insertion (0.82) per flower, as well as the high natural fruit-set indicate an efficient natural pollination system. The present study contributes for the knowledge of the diversity of reproductive strategies and nectary structures in Orchidaceae.

Anatomia foliar e caulinar de Chamaecrista trichopoda (Caesalpinioideae) e histoquímica do nectário extrafloral

Nectários são comuns dentre as Leguminosae, estando freqüentemente localizados nas folhas. Objetivou-se caracterizar anatomicamente o caule, a folha e o nectário extrafloral de Chamaecrista trichopoda, bem como investigar a natureza química do secretado do nectário dessa espécie. As amostras foram submetidas a testes histoquímicos e técnicas usuais em anatomia vegetal, sendo analisadas ao microscópio de luz e eletrônico de varredura. Os folíolos são anfiestomáticos e dorsiventrais, apresentando feixes vasculares colaterais com fibras associadas. Nas células da bainha do feixe é comum a ocorrência de monocristais. Tricomas tectores unisseriados e multicelulares ocorrem na lâmina foliar e no caule. O caule apresenta epiderme unisseriada, com três a quatro camadas de colênquima subepidérmico, seguido internamente por duas a três camadas de colênquima. Na camada mais interna do córtex destacam-se idioblastos cristalíferos contendo monocristais, o feixe vascular é delimitado por fibras e a medula é parenquimática. As características anatômicas foliares e caulinares corroboram os dados existentes para a subfamília Caesalpinioideae. O nectário situa-se na parte adaxial do pecíolo e apresenta coloração alaranjada, com o ápice formando uma concavidade, bordas levemente abauladas e pedúnculo com cerca de 1 mm de altura. É comum a ocorrência de pequenas aberturas na superfície do nectário e hifas fúngicas na fase pós-secretora. Anatomicamente, confirmou-se uma estrutura semelhante à de um nectário, o qual é vascularizado por floema e xilema; o parênquima nectarífero ocorre abaixo da epiderme que apresenta cutícula espessa. Caracteres anatômicos do nectário podem auxiliar na taxonomia do gênero. As análises histoquímicas evidenciaram o acúmulo de tanino nas células do parênquima nectarífero, que pode funcionar como uma proteção à herbivoria. Observou-se a presença de poros na superfície do nectário, que podem ser sítios preferenciais de eliminação do néctar. Entretanto, futuras análises ao microscópio eletrônico de transmissão serão fundamentais para elucidar o processo de eliminação do néctar.

Nectary structure and nectar presentation in Aloe castanea and A. greatheadii var. davyana (Asphodelaceae)

This paper deals with the nectary structure and nectar presentation of two species belonging to different sections of the genus Aloe: A. castanea (Anguialoe) and A. greatheadii var. davyana (Pictae). The development of the nectary was studied by means of bright field and fluorescence light microscopy and scanning electron microscopy (SEM) in three flower stages (young, intermediate, old). Both species have septal nectaries. In A. castanea, a subsidiary tissue, not present in A. greatheadii var. davyana, was found beneath the nectary epithelium. This tissue accumulated starch that was hydrolyzed during secretion. Starch was slightly accumulated around the nectary in A. greatheadii var. davyana. The distribution of chlorophyll in the ovary was also different in the two species. These anatomical differences are not, however, correlated with greater nectar production in A. castanea. In this species, the nectary seems to degenerate after secretion, while in A. greatheadii var. davyana no sign of degeneration was observed. Differences in nectar presentation among the two species may account for different pollinators visiting their flowers.

Nectar-secreting floral stomata in Maxillaria anceps Ames & C. Schweinf. (Orchidaceae).

Although it was generally assumed that Maxillaria spp. do not produce nectar, in recent years, nectar has been reported for a number of these orchids. Nevertheless, our current understanding of nectary structure and nectar secretion in Maxillaria is based solely on M. coccinea (Jacq.) L.O. Williams ex Hodge, which, since it shows many features characteristic of ornithophilous flowers, is atypical of this largely entomophilous genus. The aim of the present paper is to describe, for the first time, nectar secretion in a presumed entomophilous species of Maxillaria. The structure of the nectary of M. anceps Ames & C. Schweinf., nectar composition and the process of nectar secretion were investigated using light microscopy, scanning electron microscopy, transmission electron microscopy, histochemistry, refractometry and high performance liquid chromatography. Nectar appears as droplets that are exuded by modified stomata borne upon the labellar callus and collects upon the labellum and at the base of the column-foot. Although such stomata are known to occur in a number of angiosperm families, this is the first time for them to be observed in orchids. The callus consists largely of parenchyma with raphides and is supplied by eight to ten collateral bundles. This tissue, together with the single-layered epidermis, seemingly contains terpenoids. During the bud stage, the callus cells contain an organelle complement consistent with secretory cells whereas by day 4 of anthesis, much of the cell is occupied by a vacuole. The nectar is sucrose-dominant but also contains low concentrations of glucose, fructose, free amino acids and possibly terpenoids. The high sugar concentration (approx. 66 %) is consistent with melittophily and may indicate that, like the majority of Maxillaria spp., M. anceps is visited by stingless bees (Meliponini).

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.