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Floral nectar is mainly a reward in the form of food for pollinators. In early spring, when snow can still be present, pollinators have trouble finding food. The composition and productivity of nectar in flowers play an important role in a pollinator's life. It is known that low temperatures and lower humidity cause lower nectar secretion. Some studies have also shown that the quality of nectar can differ because of lower temperatures. In our research, we analysed whether abiotic factors affect nectar secretion, as well as the nectar composition of the early spring plant species Galanthus nivalis L. and Helleborus niger L. in February 2024. The study was conducted in two locations in nature. Nectar from H. niger was sampled in Tomišelj, Slovenia, whereas nectar from G. nivalis was sampled in Ljubljana, Slovenia. On four different days at three different times of day, we sampled nectar from flowers using microcapillaries. In total, we sampled 48 nectar samples from one species. We analysed soil humidity and temperature, air temperature and humidity, and UVB radiation. Our results show that nectar productivity is highest in the morning for both species. H. niger has sucrose-dominant nectar, while G. nivalis has hexose-dominant nectar. Proline, which is an important amino acid for bees, has the highest level in both species, as does the phenolic compound rutin. Environmental factors do affect nectar secretion. Soil and air temperature affect G. nivalis nectar secretion, while soil humidity affects H. niger nectar secretion. Soil and air temperature also have an effect on higher levels of sugars in both researched nectars. UVB, air humidity, and air and soil temperature seem to have an effect on phenolic compounds, but abiotic factors do not affect amino acids. [ABSTRACT FROM AUTHOR]

Rubber trees (Hevea brasiliensis) serve as the primary source of natural rubber. Their native habitat is characterized by warm and humid conditions, so they are particularly sensitive to low temperatures. Under such stress, latex burst can cause severe damage to rubber trees, which is due to the uniqueness of their economically productive parts. In order to establish a correlation between young and mature rubber trees and provide a novel prospective for investigating the mechanisms of latex burst and chilling resistance in rubber trees, the chlorophyll contents, photosynthesis, and chlorophyll fluorescence parameters in four varieties of one-year-old rubber tree seedlings were analyzed under artificially simulated chilling stress. The latex burst characteristics were subsequently recorded. A comprehensive statistical analysis of the chilling-resistance rank was conducted using the membership function method and the combination weighting method. Meanwhile, chemical compositions and tensile properties of barks from two-year-old twigs of mature rubber trees were ascertained. A correlation analysis between chilling resistance, chemical compositions, and tensile properties was performed to identify any interrelationships among them. The results showed that the number and the total area of latex-burst positions in variety Reken628 seedlings were greater than those in other varieties, and the lowest number and total area of latex-burst positions were observed in variety RRIM600 and variety PR107, respectively. With the exception of variety GT1, nectar secretion was noted in all other varieties of rubber tree seedlings under chilling stress. The chilling resistance of the four varieties decreased in the following order: variety GT1 > variety RRIM600 > variety PR107 > variety Reken628. The chilling resistance was strongly (p < 0.001) negatively correlated with cellulose content and acid-insoluble lignin content, respectively. The total area of latex burst was significantly (p < 0.001) and positively correlated with holocellulose content and maximum load, respectively. Furthermore, this study also provides new insights into the mechanism of nectar secretion induced by low temperatures and its association with the chilling resistance of rubber trees. [ABSTRACT FROM AUTHOR]

This is the first reported study aimed at nectar secretion of Satsuma mandarin cultivars from Croatia. The study was conducted in 2014-2016 on four cultivars: Kawano Wase, Okitsu, Chahara and Zorica. Nectar was collected at six measurements per day at two-hour intervals (8:00-18:00) for a total of 12 days. The mean values of nectar quantity per flower were higher in Okitsu (23.41 μL) and Kawano Wase (22.79 μL) cultivars and were not statistically different (P > 0.05) from the other cultivars, while a significant difference (P < 0.05) was found in Chahara (21.60 μL) cultivar compared to Zorica (20.01 μL). Secreted nectar ranged from a minimum of 5.00 μL to a maximum of 75.00 μL among the studied cultivars. When comparing sugar concentration by cultivars, the lowest concentration was found in the cultivar Zorica (18.43%) and differed significantly (P < 0.05) from the others, while the mean values of the studied parameter in the cultivars Okitsu (20.35%), Kawano Wase (20.66%) and Chahara (20.17%) did not differ significantly (P > 0.05). The average sugar content in flowers of all Satsuma mandarin cultivars ranged from 4.13 mg to 4.96 mg. Sugar yield ranged from 240.8 kg/ha to 289.2 kg/ha and honey yield ranged from 301 kg/ha to 361.5 kg/ha. The present study shows that the studied cultivars of Satsuma mandarin are very attractive to honey bees due to the large number of flowers producing a large amount of nectar and that the Neretva Valley is a very good area for the production of this rare unifloral type of honey.

The objective of the study was to examine the dynamics and sugar content of nectar of major bee flora species and to determine an approximate honeybee colony carrying capacity in northeast dry land areas of the Amhara region. Acacia asak, Acacia etbaica, Acacia tortolis, Becium grandiflorum, and Cordia africana honeybee floral species were selected on the basis of relative dominance in the area. Floral nectar was collected through micropipette and washing techniques based on the flower nature of the species and nectar sugar was measured by refractometer. Hence, A.asak, A.etbaica, A.tortolis, B.grandiflorum, and C.africana could have been estimated to produce 10.2 ± 6.4 mg, 5.3 ± 4.6 mg, and 2.6±1 mg. 4, 3.7 ± 2.1 mg, and 5.7 ± 3.2mg/flower head of nectar sugar, respectively. In a single tree of A.etbaica, A.asak, A.tortolis, B.grandiflorum, and C.africana a mean of 0.15 kg, 0.15 kg, 0.06 kg, 0.01 kg, and 0.03 kg of honey yield was expected to produce respectively. Similarly in a hectare of land, a mean of 49.9 kg, 128.9 kg, 5.6 kg, 5.5 kg, and 2.2 kg of honey was estimated to harvest. In a hectare of land a sum of 57.5 kg, 57.5 kg, and 128.9 kg of honey in highland, midland, and lowland locations, respectively was estimated to produce during the main harvesting season of the area. The mean number of honeybee colonies introduced in the lowland have estimated to be 18 traditional, 6 transitional, and 5 modern hives, and in the highland 12 traditional, 6 transitional, and 5 modern hives whereas in the midland 8 traditional, 5 transitional, 3 modern hives. In summary, even in the study area with limited rainfall and high temperatures, these species secreted a substantial amount of nectar sugar and supporting the enhancement of honey yield.

The structural changes in the secretory cells are important to understand the ontogeny and nectar secretion process from the nectaries. In this study, we investigated the ultrastructural changes during different developmental/secretion stages of extrafloral nectaries (EFNs) of Pithecellobium dulce. The dense cytoplasm with active biosynthesis mechanisms such as ribosomes, mitochondria, large nucleus, and plastids with accumulated starch grains characterized the pre-secretion stage of young nectariferous cells. During the secretory phase, the cytoplasm showed distinct changes associated with endomembrane transport such as the predominant occurrence of Golgi, secretory vesicles, and ER resulting in the subsequent appearance of secretions in the intercellular and subcuticular spaces. Cell wall loosening following the dissolution of middle lamellae leading to the formation of subcuticular spaces was evident during advanced stages of nectar secretion. The characteristic cytoplasmic and apoplastic changes associated with cell death were noticed during the post-secretory stages. The structural evidence from the present study suggests the occurrence of two modes of secretion (merocrine and holocrine) during the early and late stages of secretion in the EFNs of P. dulce. [ABSTRACT FROM AUTHOR]

This study aimed to determine the value of honey source on Robinia by analyzing flower morphology and nectar characteristics in floral nectar of eight selected individuals. The mean nectar volume secreted by genus Robinia was 1.7 ± 1.0 µL. Among the samples, PR (R. margaretta) and HR (R. pseudoacacia) secreted the highest and lowest nectar volumes—3.0 ± 1.1 and 1.1 ± 0.7 µL, respectively. The mean sugar concentration was 44.8 ± 6.1% (range, 40.1–51.4%). The ANOVA results revealed a statistically significant difference in nectar volume and sugar concentration among the eight individuals (p < 0.05). The free sugar content ranged from 0.39 (HR) to 0.78 (KR) mg/μL, and nectar sugar contents ranged from 0.31 (HR) to 1.53 (PR) mg per flower. The sucrose/hexose ratio ranged from 0.5 to 3.6, and sucrose was high in all samples. The results of the Kruskal-Wallis H test revealed significant differences in free sugar content (mg/µL), nectar sugar content per flower and sucrose/hexose ratio (p < 0.05). There were close correlations between nectar characteristics and flower morphology as followed; 1) nectar volume and nectar sugar content per flower (r = 0.976), 2) nectar volume and calyx length (r = 0.952), 3) sugar concentration in nectar and length of inflorescence (r = 0.952). Asparagine was the most abundant (average; 60.2%) amino acid, followed in decreasing order by alanine (6.9%), glutamine (5.2%), and serine (4.7%). The results of Kruskal-Wallis H tests showed that the rate of amino acids of alanine, glutamine, glutamic acid, and arginine significantly differed among the samples (p < 0.05). [ABSTRACT FROM AUTHOR]

The study was conducted at Main Agricultural Research Station, UAS, Raichur during rabi 2020-21 to record the floral visitors and foraging activity of pollinator on parental lines of sunflower hybrid KBSH-44. Totally, thirty species of floral visitors were recorded on parental lines of sunflower hybrid (KBSH-44), among them 15 were hymenopterans, 7 lepidopterans, 5 coleopterans and 3 dipterans. Apis dorsata was predominant pollinator (20.08 ±10.45 bees/5 capitula/5 min.) on CMS parental line (CMS-17A), followed by A. cerana and least was A. florea. The peak foraging activity of A. dorsata was recorded at 1100-1200 hr with 33 bees, A. cerana at two peaks at 0900-1100 hr (23 bees) and 1500-1600 hr (19 bees) and A. florea at 1000-1200hr (8 bees). The maximum Shannon-Wiener index of diversity (H=1.28) of floral visitors on CMS line was recorded at 0800-0900 hr and 1000-1100 hr of the day and least (H=0.56) was at 1700-1800 hr. In case of fertility restorer line (RHA-95C-1), Apis dorsata was recorded peak foraging activity at 1000-1200hr (49 bees/5 capitum/5 min.), Apis cerana at 1100-1200 hr (50 bees/5 capitulum/5 min.) and Apis florea recorded at 1100-1300 hr (25 bees/5 capitulum/5 min.). The maximum Shannon-Wiener index of diversity (H=1.32) of floral visitors on R line was recorded at 1700-1800 hr of the day and least (H=1.03) was at 0800-0900 hr. Apis dorsata was recorded highest Berger Parker dominance both in CMS line (d=0.471) and in R line (d=0.392). [ABSTRACT FROM AUTHOR]

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Mabea fistulifera, a species pollinated mainly by diurnal and nocturnal vertebrates, presents pendulous inflorescences with approximately 70 pairs of nuptial nectaries (NNs). These NNs exude voluminous nectar drops that defy gravity, remaining exposed at the inflorescence for more than a day. We aimed to investigate the NN secretory process and the unique nectar presentation of M. fistulifera. NNs and their exudate were collected at different secretory stages and submitted to structural studies and chemical analysis. The epidermis is devoid of stomata and constitutes the main site of synthesis for non-sugar metabolites found on nectar and nectar-coating film. Nectary parenchyma presents few small starch grains, and vascular strands are distributed until the nectary parenchyma cells close to the epidermis. Vascular tissues at the nectary parenchyma seem to provide sugar and water for the nectar. A film composed of lipids, alkaloids, and proteins covers the nectar drops. The film guarantees the nectar offering for several hours, as it minimizes water loss and prevents falls by gravitational action. The release of large nectar drops is intrinsically linked to the NN anatomical traits and the exudate composition. Low sugar concentration and predominance of hexoses in M. fistulifera nectar are essential for maintaining nectar exudation for many hours, which results in the visitation of a broad spectrum of pollinators. [ABSTRACT FROM AUTHOR]

Floral nectaries have evolved multiple times and rapidly diversified with the adaptive radiation of animal pollinators. As such, floral nectaries exhibit extraordinary variation in location, size, shape, and secretory mechanism. Despite the intricate ties to pollinator interactions, floral nectaries are often overlooked in morphological and developmental studies. As Cleomaceae exhibits substantial floral diversity, our objective was to describe and compare floral nectaries between and within genera. Floral nectary morphology was assessed through scanning electron microscopy and histology across three developmental stages of nine Cleomaceae species including representatives for seven genera. A modified fast green and safranin O staining protocol was used to yield vibrant sections without highly hazardous chemicals. Cleomaceae floral nectaries are most commonly receptacular, located between the perianth and stamens. The floral nectaries are supplied by vasculature, often contain nectary parenchyma, and have nectarostomata. Despite the shared location, components, and secretory mechanism, the floral nectaries display dramatic diversity in size and shape, ranging from adaxial protrusions or concavities to annular disks. Our data reveal substantive lability in form with both adaxial and annular floral nectaries interspersed across Cleomaceae. Floral nectaries contribute to the vast morphological diversity of Cleomaceae flowers and so are valuable for taxonomic descriptions. Though Cleomaceae floral nectaries are often derived from the receptacle and receptacular nectaries are common across flowering plants, the role of the receptacle in floral evolution and diversification is overlooked and warrants further exploration. [ABSTRACT FROM AUTHOR]

Although both subspecies of Pteridium aquilinum (subsp. aquilinum and subsp. pinetorum) are widespread in Poland, our knowledge about the occurrence and significance of extrafloral nectaries on frond stipes (petioles) is very limited. Their location on the abaxial stipe surface in pairs at subsequent pinna-bases is often overlooked. The study concerns the morphological/ anatomical structure, distribution, and function of the bracken nectaries. Observations of sugar secretions of the nectaries and their local associations with ants indicated a dependence on frond age, seasonality, and environmental factors. The nectaries consist of a single layer of the epidermis with stomata, secretory parenchyma, and ground parenchyma cells lying above the vascular bundles, with a hypodermal sterome composed of fibres. The anatomy of the two examined subspecies revealed a close similarity, despite the morphological differences in size, shape, colour, and secretory activity. This paper provides also a review of published data on the nectaries in P. aquilinum and other fern species. [ABSTRACT FROM AUTHOR]

Sugars are the major source of energy in living organisms and play important roles in osmotic regulation, cell signaling and energy storage. SWEETs (Sugars Will Eventually be Exported Transporters) are the most recent family of sugar transporters that function as uniporters, facilitating the diffusion of sugar molecules across cell membranes. In plants, SWEETs play roles in multiple physiological processes including phloem loading, senescence, pollen nutrition, grain filling, nectar secretion, abiotic (drought, heat, cold, and salinity) and biotic stress regulation. In this review, we summarized the role of SWEET transporters in plant development and abiotic stress. The gene expression dynamics of various SWEET transporters under various abiotic stresses in different plant species are also discussed. Finally, we discuss the utilization of genome editing tools (TALENs and CRISPR/Cas9) to engineer SWEET genes that can facilitate trait improvement. Overall, recent advancements on SWEETs are highlighted, which could be used for crop trait improvement and abiotic stress tolerance. [ABSTRACT FROM AUTHOR]

Barkeria scandens and B. whartoniana are endangered, endemic taxa from Mexico. They are epiphytes adapted to dry habitats. Since these plants are xerophytic, their flowers were investigated for structural adaptations to nectar secretion. The flowers of both species are structurally similar, and contrary to most claims for the genus, have functional floral nectaries comprising a nectary chamber and a narrow tubular cuniculus. Nectar is present in both these structures, and contains sugars and lipid-like compounds. The nectary tissue is composed of a single-layered epidermis overlying 1–2 layers of subepidermal secretory parenchyma. The outer tangential wall of the epidermal cells is thick and multi-layered, whereas the cuticle, which often shows blistering, is lamellate and possesses micro-channels. Lipid-like material occurs both between the microfibrils of the cell wall and in the micro-channels. Robust secretory tissue, thick cell walls, and lipid-like nectar components limit nectar evaporation. Moreover, the rigidity of the nectary potentially makes it possible for red-flowered B. scandens to switch from entomophily to ornithophily.

Main conclusion: The cytological changes underlying the formation of an apoplasmic barrier in the multi-layered extrafloral nectaries of Citharexylum myrianthum are compatible with the synthesis, transport and deposition of suberin. In terms of ontogenesis and function, the intermediate layers of these nectaries are homologous with the stalks of nectar-secreting trichomes. Anticlinal cell wall impregnations are common in trichomatic nectaries and their functions as endodermis-like barriers have been discussed because of possible direct effects on the nectary physiology, mainly in the nectar secretion and resorption. However, the cytological events linked to nectary wall impregnations remain little explored. This study documents the ontogenesis and the fine structure of the EFN cells, and cytological events linked to the wall impregnations of multi-layered extrafloral nectaries (EFNs) in Citharexylum myrianthum Cham. (Verbenaceae). EFNs are patelliform, and differentiated into (a) a multicellular foot, which is compound in structure and vascularised with phloem strands, (b) a bi-layered intermediate region with thickened cell walls and (c) a single-layered secretory region with palisade-like cells. EFNs are protodermal in origin, starting with a single protodermal cell and ending with the complex, multi-layered structure. The cell wall impregnations first appear in the very young EFN and increase towards maturity. Lipid patches (assumed to be suberin) are deposited on the inner faces of the primary walls, first along the anticlinal walls and then extend to the periclinal walls. On both walls, plasmodesmata remain apparently intact during the maturation of the EFNs. In the peripheral cytoplasm there are abundant polymorphic plastids, well-developed Golgi bodies often close to rough endoplasmic reticulum profiles, mitochondria and polyribosomes. Cytological events linked to the wall impregnations are consistent with suberin synthesis, transport and deposition. Our findings offer new insights into the structure-properties of specialised nectary cell walls and so should contribute to our knowledge of the physiological and protective roles of this structure in nectar glands. [ABSTRACT FROM AUTHOR]

Climate change is a global phenomenon, driven by industrialization and deforestation, which over time has led to a reduction in the ozone layer and an increase in carbon dioxide. These have led to changes in the integrity of the ecosystem and biodiversity, affecting bee colonies as well. Temperature and humidity play an important role in the secretion of nectar in honey plants, while also influencing the feeding behavior of bee colonies. The study follows the evolution of the meteorological factors mentioned, in the period 2017-2021, during the production harvests of rapeseed, acacia, linden and sunflower, in April, May, June and July. During the analyzed period, statistically significant differences were registered for the analyzed factors compared to their average (p <0.05), with negative influences on the nectar secretion and implicitly on the capitalization of the harvests. [ABSTRACT FROM AUTHOR]

Sunflower is a highly important bee floral crop. The nectar secretion governs this parameter and is greatly influenced by cultivar, environmental factors and fertilizer application. Studies were conducted at Punjab Agricultural University, Ludhiana on sunflower hybrids (PSH 996 and PSH 1962) sown on different dates (January 31, February 10, February 20 and March 2) with three levels of nitrogen (45, 60 and 75 kg ha-1). Delay in sowing from January 31 to March 2 caused significant reduction in nectar secretion (12.66%) and increase in its concentration (5.38%). The daily mean temperature had significant positive (R2 = 0.52 and 0.54) while mean relative humidity had negative (R2 = 0.55 and 0.37) correlation with nectar total soluble solids (TSS).Nectar secretion and its TSS increased significantly only at nitrogen dose of 60 kg ha-1 as compared to 45 kg ha-1.Weather parameters have more pronounced effects on TSS at 45 kg ha-1.Delay in sowing by one month resulted in reduction in honey production potential by 1.5- 1.8 kg ha-1. In addition to this, the reduced nectar availability due to delay in sowing may negatively effect in attracting and sustaining pollinators’ populations and crop yield.

Significant progress has been achieved in the use of heterosis in soybean and several soybean hybrids have been released in China. However, broad use of hybrid soybean seed is limited due to low seed setting of female parents. Breeding cytoplasmic male sterile (CMS) lines with high out-crossing rate is necessary to solve the problem. The objective of this study was to determine the relationship between out-crossing rate of CMS lines and their nectar secretion. The daily nectar secretion rhythm, meteorological effect on nectar secretion, and differences in nectar secretion among genotypes and years were investigated in 27 soybean CMS lines (A-lines) with their maintainers (B-lines) and restorers (R-lines). The correlation between out-crossing rate of CMS lines and nectar production was also evaluated. Nectar secretion had diurnal variation. Secretion initiated at about 06:00 for most materials and reached a peak at 07:00–08:30 after flower opened, then the nectar secretion decreased gradually. A sub-peak appeared at about 13:00, while the nectar could not be detected at 17:00. Nectar secretion was greatly influenced by the weather conditions. The amount of nectar secretion increased gradually over time during periods of high temperature and no rainfall for several days. Rainy weather and low temperatures inhibited nectar secretion. There were obvious variations of nectar amount among different genotypes tested. Significant nectar variation within a genotype among years was also observed, and the highest nectar secretion was 3-fold higher than the lowest. The amount of nectar secretion from R-lines was significantly higher than that of A- and B-lines. There was no significant difference in nectar secretion between A- and B-lines. A- and B-lines with higher out-crossing rates secreted more nectar. The amount of nectar secretion of A- and B-lines were significantly positively correlated with the out-crossing rate of A-lines.

Premise: Floral rewards are essential in understanding floral function and evolution of the relationships between flowers and pollinators. Whether sugars are present in stigmatic exudates in Anthurium and whether it has floral nectaries have remained controversial because of the scarcity of structural studies. To solve these questions, we investigated the floral anatomy of A. andraeanum to elucidate whether (1) tepals are secretory organs, (2) tepals possess a structurally recognizable nectary, and (3) tepalar secretion differs from stigmatic secretion. Methods: Floral structure was assessed through light and electron microscopy of samples of immature, pistillate, and staminate flowers. The dynamics of the starch reserve was investigated using histochemical tests, and the sugar content in the floral exudates was assessed using thin‐layer chromatography. Results: Sugar analysis did not detect sucrose, glucose, or fructose in stigmatic secretions, but confirmed their presence in tepalar secretions. Stigmatic secretion was produced by secretory stigmatic papillae; tepalar exudates were produced by nonvascularized nectaries in the apex of tepals. These nectaries were characterized by modified stomata and cells with cytoplasm rich in organelles, and a high content of calcium oxalate crystals. Conclusions: Our results showed for the first time nectaries on tepals and true nectar secretion for A. andraeanum. Stigmatic secretion appears to be a distinct substance, and its often‐reported sugar content seems to be a result of sample contamination. Nectar and stigmatic secretions have been often mistaken in other Anthurium species and deserve a revision for this genus. [ABSTRACT FROM AUTHOR]

Sunflower is a highly important bee floral crop. The nectar secretion governs this parameter and is greatly influenced by cultivar, environmental factors and fertilizer application. Studies were conducted at Punjab Agricultural University, Ludhiana on sunflower hybrids (PSH 996 and PSH 1962) sown on different dates (January 31, February 10, February 20 and March 2) with three levels of nitrogen (45, 60 and 75 kg ha-1). Delay in sowing from January 31 to March 2 caused significant reduction in nectar secretion (12.66%) and increase in its concentration (5.38%). The daily mean temperature had significant positive (R² = 0.52 and 0.54) while mean relative humidity had negative (R² = 0.55 and 0.37) correlation with nectar total soluble solids (TSS). Nectar secretion and its TSS increased significantly only at nitrogen dose of 60 kg ha-1 as compared to 45 kg ha-1. Weather parameters have more pronounced effects on TSS at 45 kg ha-1.Delay in sowing by one month resulted in reduction in honey production potential by 1.5-1.8 kg ha-1. In addition to this, the reduced nectar availability due to delay in sowing may negatively effect in attracting and sustaining pollinators' populations and crop yield. [ABSTRACT FROM AUTHOR]

Pollination is essential for efficient reproduction in pollinator-dependent crops that rely on the attraction of pollinators to flowers. Especially, floral nectar is considered to be an important factor attracting pollinator like honey bees, but differences among major chestnut species (Castanea crenata, C. mollissima, C. dentata, and C. sativa) are still little explored. This study aims to evaluate the value of honey source by analyzing floral nectar characteristics and comparing the composition of volatile organic compounds (VOCs) that mediate plant-pollinator interaction. In this study, we analyzed nectar samples obtained from male flowers using HPLC and HS-SPME/GC–MS. The five chestnuts showed significant differences between the volume of secreted nectar, free sugar composition, amino acid content and VOCs composition. Furthermore, C. crenata (Japanese cultivar ‘Ungi’) was revealed to emit the highest total amounts of VOCs and high levels of benzenoid compounds that are generally associated with flower-visiting insects. The sugar content per catkin, which is used to determine the honey yield, was the highest in C. crenata, suggesting that C. crenata ‘Ungi’ can be highly valued as a honey tree. Therefore, a better understanding of the relationship between pollinator and nectar characteristics of C. crenara could contribute to a prospective honey plant.

The presence of nectarless flowers in nectariferous plants is a widespread phenomenon in angiosperms. However, the frequency and distribution of nectarless flowers in natural populations, and the transition from nectariferous to nectarless flowers are poorly known. Variation in nectar production may affect mutualism stability, since energetic resource availability influences pollinators’ foraging behavior. Here, we described the spatial and temporal nectar production patterns of Jacaranda oxyphylla, a bee-pollinated species that naturally presents nectarless flowers. Additionally, we compared nectariferous and nectarless floral disks in order to identify histological, subcellular and chemical changes that accompanied the loss of nectar production ability. For that we used standard methods for light and transmission electron microscopy, and gas chromatography coupled to mass spectrometry for chemical analyses. We verified that 47% of flowers did not produce nectar during the whole flower lifespan (nectarless flowers). We also observed remarkable inter-plant variation, with individuals having only nectarless flowers, others only nectariferous ones and most of them showing different proportions of both flower types, with variable nectar volumes (3–21 μl). Additionally, among nectariferous flowers, we registered two distinct rhythms of nectar production. ‘Early’ flowers produced nectar from 0 to 24 h, and ‘late’ flowers produced nectar from 24 to 48 h of anthesis. Although disks from nectariferous and nectarless flowers displayed similar histological organization, they differed strongly at subcellular level. Nectariferous (‘early’ and ‘late’) flowers exhibited a cellular apparatus typical of nectar secretion, while nectarless flowers exhibited osmophoric features. We found three aliphatic and one aromatic compound(s) that were detected in both the headspace of flowers and the disks of nectarless flowers, but not the disks of nectariferous flowers Although the remarkable variation in nectar availability may discourage pollinator visits, nectarless flowers might compensate it by producing volatile compounds that can be part of floral scent, acting as chemical attractants. Thus, nectarless flowers may be helping to maintain pollination in this scenario of trophic resource supply scarcity. We suggest that J. oxyphylla can be transitioning from a nectar-based pollination system to another resource-based or even to a deceit mechanism of pollination.

The aim of the current study was to determine the floral phenology, nectar secretion dynamics, and honey production potentials of two naturally growing lavender species (L. dentata and L. pubescens), in southwestern Saudi Arabia. In both species, flowering is continuous. This means that, when open flowers on a spike are shaded, new flowers emerge. Such a flowering pattern might be advantageous to the plant to minimise competition for pollinators and promote efficient resource allocation. The flowering periods of the two species overlap. Both species secreted increasing amounts of nectar from early morning to late afternoon. The mean maximum volumes of accumulated nectar from bagged flowers occurred at 15:00 for L. pubescens (0.50 ± 0.24 μL/flower) and at 18:00 for L. dentata (0.68 ± 0.19 μL/flower). The volume of the nectar that became available between two successive measurements (three-h intervals) varied from 0.04 μL/flower to 0.28 μL/flower for L. pubescens and from 0.04 μL/flower to 0.35 μL/ flower for L. dentata, This variation reflects the differences in the dynamics of nectar secretion by these species, and indicates the size of the nectar that may be available for flower visitors at given time intervals. The distribution of nectar secretions appears to be an adaptation of the species to reward pollinators for longer duration. Based on the mean amount of nectar sugar secreted by the plants, the honey production potentials of the species are estimated to be 4973.34 mg and 3463.41 mg honey/plant for L. dentata and L. pubescens, respectively.

Abstract: Lilium auratum var. platyphyllum, which is endemic to the Izu Islands, has white petals and emits a strong floral scent, typical of moth‐pollinated plants. Moths might be important pollinators within the Izu Islands because swallowtail butterflies are absent or rare there. Therefore, we investigated insular var. platyphyllum and widespread L. auratum var. auratum on the mainland of Japan to clarify the relationship between floral characteristics and pollinators. Measurement of floral scent intensity using an odor sensor indicated that the intensity increased in the evening and at night in var. platyphyllum, whereas intensity increased at night in var. auratum. Total sugar weight in nectar, which was calculated by nectar volume and sugar concentration, showed that the flowers of var. platyphyllum secreted nectar abundantly both in the evening and at night, whereas those of var. auratum secreted an almost constant amount of nectar throughout the day. Flower visitor assemblages and their frequencies studied using digital cameras suggested that crepuscular and nocturnal hawkmoths are important pollinators for var. platyphyllum. In contrast, both diurnal swallowtail butterflies and nocturnal large hawkmoths are important and effective pollinators for var. auratum. These conclusions were also supported by the exclusion experiments of either diurnal or nocturnal flower visitors using mesh bags. The rates of seed sets of var. platyphyllum were significantly higher from nocturnal pollination than from diurnal pollination. Thus, this study revealed that floral traits of var. platyphyllum show more adaptation for crepuscular and nocturnal hawkmoths, which are relatively abundant in the Izu Islands, than those of var. auratum. [ABSTRACT FROM AUTHOR]

The presence of nectarless flowers in nectariferous plants is a widespread phenomenon in angiosperms. However, the frequency and distribution of nectarless flowers in natural populations, and the transition from nectariferous to nectarless flowers are poorly known. Variation in nectar production may affect mutualism stability, since energetic resource availability influences pollinators' foraging behavior. Here, we described the spatial and temporal nectar production patterns of Jacaranda oxyphylla, a beepollinated species that naturally presents nectarless flowers. Additionally, we compared nectariferous and nectarless floral disks in order to identify histological, subcellular and chemical changes that accompanied the loss of nectar production ability. For that we used standard methods for light and transmission electron microscopy, and gas chromatography coupled to mass spectrometry for chemical analyses. We verified that 47% of flowers did not produce nectar during the whole flower lifespan (nectarless flowers). We also observed remarkable inter-plant variation, with individuals having only nectarless flowers, others only nectariferous ones and most of them showing different proportions of both flower types, with variable nectar volumes (3-21 ml). Additionally, among nectariferous flowers, we registered two distinct rhythms of nectar production. 'Early' flowers produced nectar from 0 to 24 h, and 'late' flowers produced nectar from 24 to 48 h of anthesis. Although disks from nectariferous and nectarless flowers displayed similar histological organization, they differed strongly at subcellular level. Nectariferous ('early' and 'late') flowers exhibited a cellular apparatus typical of nectar secretion, while nectarless flowers exhibited osmophoric features. We found three aliphatic and one aromatic compound(s) that were detected in both the headspace of flowers and the disks of nectarless flowers, but not the disks of nectariferous flowers Although the remarkable variation in nectar availability may discourage pollinator visits, nectarless flowers might compensate it by producing volatile compounds that can be part of floral scent, acting as chemical attractants. Thus, nectarless flowers may be helping to maintain pollination in this scenario of trophic resource supply scarcity. We suggest that J. oxyphylla can be transitioning from a nectar-based pollination system to another resource-based or even to a deceit mechanism of pollination. [ABSTRACT FROM AUTHOR]

Apart the linden trees are important as source of wood and have medicinal and ornamental uses, they are also important from the melliferous point of view, being a good source of food for melliferous insects as well as an important honey source for beekeepers. Among the different linden species, the silver linden is appreciated to have a good melliferous potential. Taking into account these aspects, the aim of this study was to investigate the melliferous potential of the silver linden trees (Tilia tomentosa Moench.) growing in the forests from South Romania. In this respect, a study was carried out in the years 2009, 2010 and 2011 in two forests located in South Romania. The following parameters were analyzed: 1) the average sugar yield of the silver linden flowers, which is given by the quantity of nectar secreted by the flowers and the nectar concentration in sugar; 2) the number of flowers per silver linden tree and per hectare; 3) the lifespan of the silver linden flowers. Our study performed in the two forests from South Romania showed the good melliferous potential of the silver linden trees, which was in average of 318 kg.ha-1 of honey, respectively 0.76 kg of honey per linden tree. However, it must be taken into account the influence on this good melliferous potential of the silver linden trees determined by the climatic conditions of the year and the number of flowers the linden trees can produce in the respectively year, as well as the number of linden trees from the forest. [ABSTRACT FROM AUTHOR]

During the evolutionary history of flowering plants, the appearance of floral nectaries allowed the replacement of pollen by nectar to attract pollinators, allowing lower costs involved in animal pollination by reducing the consumption of pollen. In the hybrid seed productions of entomophilous crops, knowing the levels of nectar secretion of the different lines, the male fertile (MF) and the male sterile (MS) ones, is important to maximize pollen transfers between them. In this study, we start with a review of current methods used to measure nectar secretion, and choose the one that provides a gross secretion rate in order to use it on two winter oilseed rape (Brassica napus L.) lines, the hybrid F1 'Exocet' and its MS parent. We show that oilseed rape has a gross nectar secretion rate that is constant over a period of 6-8 hours during daylight hours, that it has a thermal optimum included between 20 °C and 30 °C, and that the parental MS line secretes about half as much as the hybrid F1 one. These results enable us to propose a rigorous method to compare nectar secretions between lines and varieties. We conclude with the main other variables that should be taken into account to estimate the total amount of nectar produced by a given area of crop. [ABSTRACT FROM AUTHOR]

Many descriptions of prey capture by Dionaea muscipula (Venus flytrap) in popular publications and educational literature are inaccurate. Here we review well documented literature on prey capture in this plant's natural habitat and add observations on prey capture and attraction mechanisms we have observed in plants cultivated in a greenhouse and garden. Despite its common name "Venus flytrap" does not specialize in capturing flies. About 70% of the prey it captures in its native habitat consists of spiders, ants, and beetles. Flies are only oneto-eighteen percent of what it captures. In a greenhouse where flies, capable of entering the vents, composed most of the available prey, over 90% of the prey captured were flies. Dionaea cultivated in a garden captured a diverse array of animals, only about 37% of which were flies. Dionaea is a generalist, capturing a wide variety of prey species. Its capture mechanism does not appear to have a "syndrome" analogous to the Pollination Syndrome in flowers where a specific floral type is pollinated by a specific animal (i.e. Bee Flowers or Fly Flowers). The measured capture rates of Dionaea are low, about one capture/leaf/month in its native habitat. Similar but lower rates were measured in the greenhouse and garden. The single measurements in each habitat need to be repeated, but the low rates are consistent with the observation that wherever it is observed Dionaea has nearly all of its traps open. Both the low capture rates and the large number of open traps suggests that alluring agents drawing prey either do not exist or are ineffective. Despite reports of nectar secretion by Dionaea traps, our observations show that unstimulated traps are always dry unless wet by rain, condensation, or a sprinkler system. Secretion occurs only after prey capture. Alluring glands along the outer trap margin have been reported to be visited by small ants that work their mouthparts over the glands. We have photographed a fly exhibiting the same behavior. The exact nature of this behavior needs to be further investigated, but it does not appear that this attractant can act at a distance since flies are as likely to land on the outside of a trap as on the inside. Darwin proposed that the trap closure mechanism allows small prey to escape, preventing the expenditure of energy on captures likely to be of little benefit. Recent measurements of prey captures indicate that traps show little selectivity based on prey size and that while traps could, in theory, select larger prey, statistically they do not behave this way. [ABSTRACT FROM AUTHOR]

Nectar secretion and nectar chemistry in the flowers of comfrey (Symphytum officinale L.) were examined in the four stages of anthesis: large buds, before pollen exposure: II - freshy opened flowers with the beginning of anther dehiscence: III- completely opened flowers in the maximum of pollen exposure: lV- flowers at the final stage of anthesis, without pollen in the anthers. Individual flower stays fresh 2,5-3 days, on average. Disc-shaped nectaries of S.officinale are located at the base of the four-lobbed ovary. Nectar is released through the modified stomata. Start of nectar secretion was noted at the bud stage. Nectar volume, mass of nectar and sugars differed in the examined stages of anthesis and the biggest values were noted at the final stages. Dominant sugar in nectar was sucrose with smaller amounts of fructose and glucose. The presence of amino acids was also recorded.

This study on blooming biology, nectar secretion, pollen production and insect visitation of Aquilegia vulgaris L. was carried out in 2009 and 2011 in Lublin. The peak of flower opening during the day was between 5.00 and 7.00 (GMT +2). The flowers are protandrous with the female phase beginning approx. on the 3rd day of anthesis. The dynamics of nectar secretion and pollen shed from anthers (progressing from the central part of the androecium outwards) support the reproductive system. The amount of nectar accumulated in the spurs increased from the bud stage and was the highest in the phase with approx. ¾ of dehisced anthers, usually on the 3rd day of flower life. Then, towards the end of anthesis, the amount of secreted and accumulated nectar decreased. The number of anthers developed per flower varied from 41 to 61 (mean = 49.1). The mass of pollen per 100 anthers averaged 6.7 mg. Pollen production per flower (mean = 3.28 mg) slightly varied between years and was mainly correlated with the number of developed anthers. Estimated pollen yield was 1.69 g per m2 and sugar yield 1.22 g per m2. Species from the genus Bombus were the main flower visitors, with B. terrestris being the most frequent forager.

In this study, the micromorphology of nectaries in Echium russicum J. F. Gmel. flowers was determined by using scanning electron microscopy (SEM) and their anatomy by using light microscopy (LM). The rate of nectar production of flowers and sugar concentration in nectar were investigated. The nectary gland is located below the ovary of the pistil. It is composed of 4 parts corresponding to the parts of the ovary. The widest regions of the nectar-producing tissue are situated by the furrows separating the adjacent parts of the ovary. Nectar is secreted through anomocytic stomata, located only in the lower part of the nectary. The stomata were distributed evenly or they formed clusters of 2-3. The average number of stomata on the surface of the whole nectary was 184. At the nectar secretion stage, open and closed, as well as not fully mature stomata were observed. The orientation of most of the stomata was parallel to the nectary base. The cuticle surface of the cells of the upper and lateral part of the nectary was smooth, whereas in the region producing stomata it showed various folds facilitating the retention of nectar. The flowers produced nectar throughout the flowering period. The weight of nectar secreted throughout the lifetime of ten flowers was, on the average, 20 mg, with the concentration of sugars of 58% and their weight reaching 17 mg.

The nectar secretion of Ziziphus flowers was studied by removing and measuring the nectar every four hours, for two consecutive days, from 88 flowers of four trees (‘repeated sampling’). In another 120 flowers from the same trees, the accumulated sugar was measured at the end of the flowering stage. The mass of the nectar sugar was determined following the washing technique. The total amount of sugar per tree was calculated by multiplying the number of flowers per tree by the average mass of nectar sugar secreted per flower. The average mass of sugar produced per flower in repeated sampling was 0.79±0.54 mg/flower (range 0.09 - 2.48 mg). The average mass of sugar per flower for each of the four investigated trees was 1.43±0.53 mg, 0.72±0.27 mg, 0.94±0.39 mg and 0.37±0.26 mg, respectively. The differences among trees was statistically significant. For accumulated nectar, the overall average mass of sugar per flower was 0.55±0.23 mg (range 0.06 - 1.29 mg) and the average values for flowers on the investigated trees of Z. spina-christi were 0.69±0.26 mg, 0.41±0.16 mg, 0.51±0.16 mg and 0.53±0.21 mg; these variations were statistically significant. The average mass of nectar sugar calculated for the flowers with accumulated nectar sampling was significantly lower than the average mass of sugar recorded for repeated nectar sugar samplings (0.79±0.54 mg). According to this study, one Ziziphus tree is estimated to produce 3.6 kg of honey (range 2.2 - 5.2 kg), equivalent to about 900 kg of honey/ha (range 550 - 1300 kg). These figures indicate the high potential value of the plant for honey production. Nectar secretion was positively correlated with temperature, indicating the adaptation of the tree to hot climates.

In the years 2004-2006, flowering dynamics and nectar secretion of Phacelia campanularia A. Gray flowers as well as the insect visitation rate were studied in the climatic conditions of Lublin, Poland. The flowering of phacelia started in the middle of June and lasted for 1.5 up to 2 months. Full bloom occurred between the third and fifth week of the flowering period of this taxon. For the study period, the average weight of nectar produced by 10 flowers was 75.64 mg, weight of sugars 11.31 mg, while their concentration in the nectar was 20.2%. Among the entomofauna foraging on the flowers of phacelia, honey bees were predominant, with their proportion among the pollinators accounting for 84.8%.

A study of Hosta fortunei Baker L. H. Bailey (Funkiaceae) flowers was conducted in the years 2007 - 2008. The flower life span and flowering duration as well as the nectar production rate were determined. The structure of the tissues of the stigma and nectary was investigated using stereoscopic, light and scanning electron microscopy (SEM). The plants flowered over a period of five weeks. Flowers of H. fortunei lived two days, on the average. Developed a pistil with an elongated ovary terminating in a discal stigma. On the surface of the stigma, unicellular glandular trichomes grew densely, composed of a stalk with a length of 113 - 213 µm and a head which was characterised by a large diameter range of 54 - 96 µm. The cuticle on the apical surface of a part of the trichomes was smooth, whereas it was striated on the stalk. Their protoplast was characterised by dense cytoplasm and weak vacuolisation. In the head of the trichomes fatty substances were accumulated. Septal nectaries occurred in the ovary of the superior pistil. Nectar was exuded onto the surface through three openings, situated in the upper part of the ovary of the pistil. At these places, epidermal cells formed a smooth or slightly wrinkled cuticle. The outer walls of the cells of the epidermis covering the duct accumulating nectar were thick. The glandular tissue of the nectary was made up of 2 layers of different-shaped, thin-walled cells and a deeply stained protoplast. They contained dense cytoplasm and a large, frequently lobate nucleus. At the final stage of secretion, fine vacuoles were observed in the cytoplasm of the glandular cells. Nectar secretion was abundant. In its initial stage, secretion droplets, increasing during the activity of the glandular tissue, were observed on the epidermis surface around the nectar openings. The weight of nectar from 10 flowers was 92.41 mg. The sugar concentration in the nectar was within a range of 23% - 30%, with an average value of 26%. Sugar yield was 23.83 mg/from 10 flowers.

The investigations were carried out using light and scanning electron microscopy. The flowers of Elaeagnus commutata grow in clusters of 1-4 in the leaf axils. They are actinomorphic, four-lobed, with a single perianth that is yellow from the adaxial side, while the abaxial side is silvery-white. Peltate hairs of different structure are found on both surfaces of the sepals. The conical epidermal cells of the lobes are covered with a thick striated cuticle. Cylindrical hairs were observed on the edges of the lobes. Peltate hairs also grew on the style. The dish-shaped nectary gland is located at the base of the style. Nectar is secreted through numerous, evenly distributed stomata located above or at the level of other epidermal cells. Different stages of stomatal development are evidence of the asynchronous functioning of the stomata. The nectary consists of small epidermal cells and 5-6 layers of secretory parenchyma. The deeper layers of the gland are composed of larger cells of subglandular parenchyma in which vascular bundles supplying the nectary run. Honey bees were the main pollinators of silverberry. Ten silverberry flowers produced an average of 12 g of nectar with a sugar concentration in the 29.5-34.5% range. The weight of pollen produced by 10 flowers was 3.33 mg.