Flower and nectar attributes of pepper (Capsicum annuum L.) plants in relation to their attractiveness to honeybees (Apis mellifera L.)

Flower morphology, nectary structure, nectar traits and rates of honeybee foraging on pepper plants were studied. The nectary appears as swellings on the basal part of the ovary. The nectariferous cells are smaller and denser than the neighbouring parenchyma. Stomata are present in the nectary epidermis, but do not appear on the other parts of the ovary epidermis. Seven pepper breeding lines were grown near a bee yard in Rehovot. Five to six fold differences in nectar volume were found between the extreme genotypes. Nectar volumes were higher during noon and afternoon hours, as compared with morning hours. High correlation coefficients between nectar volume and sugar concentration were found. These were significant for the four high nectar yielding genotypes, ranging between r = 0.65 to r = 0.94. Male-fertile flowers produced more nectar and higher sugar concentration than sterile ones. Skewed distribution was observed in nectar volume of F₂ populations, but relatively low heritability values were calculated. Pepper nectar contains fructose and glucose only. The former occupies 52–82 % of the total sugar content. Pepper genotypes varied in frequency of honeybee visits and significant correlation between sugar quantity and number of honeybee visits per flower was evident. Fertile pepper flowers are not very attractive to honeybees and male-sterile flowers are even less so. The considerable variation in nectar characteristics can be exploited to increase attractiveness to honeybees, thus facilitating bee pollination in commercial production of F₁hybrid seeds and improve fruit quality.     

Floral Nectaries of Rosmarinus officinalis L. Structure, Ultrastructure and Nectar Secretion

The nectary of Rosmarinus officinalis L. has the form of a four-lobed,asymmetrical disc situated around the base of the ovary. Thenectary lobe facing the lower flower lip is enlarged and isthe only one to have modified stomata. Vascular strands consistingof phloem only occur in the nectariferous tissue. It is suggestedthat the pre-nectar originating in the phloem accumulates primarilyas starch grains in plastids of the nectariferous cells. Thenumber of grains is very large before anthesis and decreasesconsiderably at anthesis. The transport of the pre-nectar tothe various nectariferous cells appears to be mainly via thesymplast. It could not be determined whether the process ofelimination of the nectar is solely eccrine or partly granulocrine. Rosmarinus officinalis, nectary, nectar secretion, starch grains, phloem     

Development and Ultrastructure of Cucurbita pepo Nectaries of Male Flowers

The development of the nectary of the male flower ofCucurbitapepo L. was studied from 5d before to 2d after anthesis. Thenectary consists of parenchyma that stores starch in the presecretorystages, and epidermis. An hour before nectar secretion begins,the starch is hydrolyzed. The nectar exudes from the stomataand forms a continuous layer on the nectary surface. Duringanthesis the nectar may all be collected by pollinators or someor all of it may remain in the nectary and be successively resorbed.The nectary parenchyma stores material for synthesizing thesugar component of nectar and stores similar material againafter nectar resorption. It is also responsible for nectar productionand secretion. The epidermis is actively involved in the reabsorptionprocess. The resorption of nectar is a phenomenon that allowsthe plant to recover invested energy. Few observations on thisphenomenon have hitherto been published. Amyloplasts; Cucurbita pepo L.; courgette; nectaries; Nectar resorption; plastid; secretion; starch     

Floral Nectar Secretion and Ploidy in Brassica rapa and B. napus (Brassicaceae). II. Quantified Variability of Nectary Structure and Function in Rapid-cycling Lines

Haploid, diploid and tetraploid lines ofBrassica rapaL. (syn.campestris),and allotetraploidB. napusL., were examined to determine theinfluence of ploidy on floral features, particularly nectarymorphology and anatomy, and to relate nectary structure to nectarproduction capacity. Except for haploids, all lines were rapid-cycling.Average flower dry weight, and petal length and width, werein the descending orderB. napus>B. rapa (4n) >2n>n.Pollen grains of 4nplants were larger than those of 2nplants;haploids lacked pollen. All lines developed nectaries. Typically, each flower producedtwo pairs of nectaries, of different types and nectar productioncapacity. Normally, each lateral gland was located above thebase of a short stamen, and together this pair yielded mostof a flower 's nectar carbohydrate. Each median nectary aroseat the outer junction of the bases of two adjacent long stamens.All lateral nectaries received a vascular supply of phloem alone,but median glands received reduced amounts of phloem, or lackedvasculature altogether. Most nectaries were solitary, but 14%of all flowers, and especially those of 2n B. rapa,had at leastone median and lateral gland connected. Obvious variation existed in nectary morphology between ploidylevels, between flowers of the same plant, and even within flowers.Ten forms of each nectary type were recognized. Plants producingthe most nectar carbohydrate had high frequencies of lateralnectaries which were symmetrical, unfurrowed swellings. TetraploidsofB. rapahad both the highest frequencies of furrowed lateralglands, and of isolated segments of nectarial tissue at thatposition. Even these separated nectarial outgrowths receivedphloem and produced a nectar droplet. At the median location,nectaries were commonly of two forms: peg- or fan-shaped. Lobeson median nectaries, up to four per nectary, were detected inalmost half of glands of 4nflowers examined; lobes were absentin haploids. Brassica rapa; Brassica napus; flower size; nectar production; nectary variability; petal size; ploidyphloem; pollen; rapeseed     

Ultrastructure and Function of Floral Nectaries of Chamelaucium uncinatum (Myrtaceae)

Nectar is secreted for up to 11d after anthesis inChamelauciumuncinatum . The volume and sucrose concentration secreted variesbetween flowers, plants and days. The period of nectar secretioncoincides with the period of pollen presentation and stigmaticreceptivity suggesting nectar is part of an efficient reproductivestrategy inC. uncinatum . The nectary ofC. uncinatum consistsof the entire upper surface of the ovary and hypanthium. Theepidermis of the nectary is covered by a thickened cuticle whichis only broken at the sites of the numerous modified stomatawhich are scattered across its surface. It is suggested thatnectar is secreted onto the surface of the ovary via these modifiedstomata. The presence of extensive and well developed endoplasmicreticulum, mitochondria and Golgi bodies in the nectar secretingcells indicates that a granulocrine mechanism of secretion isoccurring inC. uncinatum . Chamelaucium uncinatum ; Geraldton Waxflower; floral nectaries; nectar production; modified stomata     

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright‐coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand‐, self‐ and cross‐pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.     

Floral Nectar, Nectary Structure and Pollinators in Some Argentinean Bromeliaceae

The floral nectar chemical composition and nectary structureof some Argentinean Bromeliaceae were studied, including fieldobservations on pollinators. Twenty species belonging to eightgenera from the three subfamilies were analysed. The nectarcomponents report is mostly new since no comprehensive studyhas been carried out on the family previously. Sugars were alwayspresent, while alkaloids, lipids, phenols, and proteins werenot detected in any sample. Reducing acids were found in threespecies. Amino acids were detected in a very low concentrationin only about half the samples. Pitcairnioideae species showa mean balanced disaccharide/monosaccharide nectar sugar composition,Bromelioideae had hexose-rich nectars and Tillandsioideae saccharose-dominantones. Nectar concentration ranged from 16 to 48 %. All taxabear septal nectaries with many common features. Pitcairnioideaeand Tillandsioideae members have half-inferior ovaries, a featuremostly overlooked in previous studies. Three types of nectaryarchitecture were recognized in both subfamilies. Bromelioideaehave inferior ovaries and possess comparable nectaries. Hummingbirdsconstitute the main flower pollinators of many species but butterfliesand bees were occasionally seen in two species, cropping nectarand pollen, respectively. Argentinean Bromeliaceae,, floral nectar, nectary structure, pollinators, alkalinity, abromeitiella, Aechmea, Bromelia, Deuterocohnia, Dyckia, puya, Tillandsia, vriesea     

Enhanced UV-B radiation,flower attributes and pollinator behaviour in Cistus creticus: a Mediterranean field study

The aim of this investigation was to examine the reasons for the higher pollination success in Cistus creticus under enhanced UV-B radiation (Stephanou & Manetas 1998). Thus, a selected array of floral attributes as well as the frequency and duration of insect visits were studied in the field under ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3° N, 29.1° E). Video-recording revealed two categories of visitors, i.e. true pollinators (bees) and nectar thieves. The frequency of visits to both control and UV-B treated plants was the same and independent of whether the UV-B tubes were on or off during video recording. UV-B radiation had no effect on gross floral morphology (petal surface area, number of pollen grains, stamens and ovules, optical properties of petals and stamens), yet nectary size was almost doubled. In addition, the duration of insect visits was significantly longer on UV-B treated plants, provided that the UV-B tubes were off during monitoring. The differences were abolished during the part of the day that the tubes were on, indicating that the insects were annoyed by supplemental UV-B radiation. These results are consistent with the nectaries producing larger quantities of nectar, which caused the insects to stay longer on flowers of UV-B treated plants and improved pollination success.     

Ultrastructure, Development and Secretion in the Nectary of Banana Flowers

The nectaries of Musa paradisiaca L. var. sapientum Kuntze werefound to secrete in addition to the sugar solution, a polysaccharidemucilage and a very electron dense, homogenous material whichwas apparently protein. The polysaccharide had already startedto appear outside the epithelial cells of the nectary at veryearly stages of nectary development. At somewhat later developmentalstages the very dense homogenous material appeared in the formof droplets between the plasmalemma and cell wall in massesin the nectary lumen. Nectar secretion started in flowers whenthe bract in the axil of which they occurred had just recoiled.The ER elements were dilated and formed vesicles and the Golgibodies were very active, at the stage of the nectar secretionand at stages preceding it, except at the stage just beforesecretion. In all stages of nectary development the dilatedER elements and most large Golgi vesicles contained fibrillarmaterial. It is suggested that both ER and the Golgi apparatusare involved in the secretion of the sugar solution and of thepolysaccharides. There was not enough evidence as to where inthe cell the very dense homogenous material is synthesized. A few developmental stages of the nectaries of the male flowersof the Dwarf Cavendish banana, which do not secrete nectar,were also studied. It was seen that at early stages of development,the ultra-structure of the nectary of this banana variety wassimilar to that of M. paradisiaca var. sapientum. However, theepithelial nectary cells of the Dwarf Cavendish banana disintegratedbefore maturation of the nectary. Musa paradisiaca L, banana, floral nectaries, ultrastructure     

Intraplant variation in nectar traits in Helleborus foetidus (Ranunculaceae) as related to floral phase, environmental conditions and pollinator exposure

Factors that contribute to variation in nectar sugar composition, nectar concentration and volume have been a central concern in studies of pollinator assemblages in angiosperms. In an effort to better understand the mechanisms underlying variation in nectar traits, we designed a series of experiments with flowering Helleborus foetidus individuals under natural and glasshouse conditions, to identify intraplant variation in nectar traits which depend on both intrinsic (sexual phases of individual flowers) and external (pollinator visits and plant growth conditions) factors. The results showed that nectar volume, sugar composition and concentration in Helleborus foetidus varied between floral sexual phases, environmental growing conditions, and levels of flower exposure to pollinator visits. Processes of mate-limitation in male reproductive success or pollen-limitation in female success, as well as flower protogyny and holocrine secretion of nectaries may be involved in nectar variability between floral phases. By comparing different environments we observed that nectar volume and concentration at the nectary and flower level were plastic traits sensitive to external conditions, emphasizing responsiveness to environmental changes and a consequent plasticity in nectar traits such as sugar concentration and volume. Nectar sugar composition did not respond to different growing conditions, suggesting that this is an intrinsic characteristic of this species, but pollinator exposure produced significant changes in the nectar of single nectaries, particularly in the sucrose-fructose balance. Future research on nectar ecology and nectar chemistry will need to consider that nectar traits exhibit different kinds of variation at the intraplant level and under different environmental conditions.     

Floral Nectar, Nectary Structure and Pollinators in Some Argentinean Bromeliaceae

The floral nectar chemical composition and nectary structureof some Argentinean Bromeliaceae were studied, including fieldobservations on pollinators. Twenty species belonging to eightgenera from the three subfamilies were analysed. The nectarcomponents report is mostly new since no comprehensive studyhas been carried out on the family previously. Sugars were alwayspresent, while alkaloids, lipids, phenols, and proteins werenot detected in any sample. Reducing acids were found in threespecies. Amino acids were detected in a very low concentrationin only about half the samples. Pitcairnioideae species showa mean balanced disaccharide/monosaccharide nectar sugar composition,Bromelioideae had hexose-rich nectars and Tillandsioideae saccharose-dominantones. Nectar concentration ranged from 16 to 48%. All taxa bearseptal nectaries with many common features. Pitcairnioideaeand Tillandsioideae members have half-inferior ovaries, a featuremostly overlooked in previous studies. Three types of nectaryarchitecture were recognized in both subfamilies. Bromelioideaehave inferior ovaries and possess comparable nectaries. Hummingbirdsconstitute the main flower pollinators of many species but butterfliesand bees were occasionally seen in two species, cropping nectarand pollen, respectively. Argentinean Bromeliaceae, floral nectar, nectary structure, pollinators, Abromeitiella, Aechmea, Bromelia, Deuterocohnia, Dvckia, Puva, Tillandsia, Vriesea     

The systematic significance of floral morphology,nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.     

The Floral Nectary ofDigitalis purpureaL., Structure and Nectar Secretion

The floral nectary of the foxglove (Digitalis purpureaL.), locatedat the base of the ovary, was examined by: scanning electronmicroscopy; quantitative bright-field microscopy via computer-aided3-D reconstruction from serial sections; morphometric procedures;transmission electron microscopy and measurement of nectar effluxunder different experimental conditions. Time-lapse video recordingvia a microscope with incident light clearly showed that thenectar escaped from the apertures of modified stomata. The volumeflux via individual stomatal apertures was 0.31±0.1 nlmin^-1; therefore only a fraction of the total number of stomataper nectary (115±8) would be sufficient to dischargethe amount of nectar reported in previous publications. Thestomatal apertures are continuous with intercellular spacestraversing the small-celled nectariferous tissue. The latteris vascularized only by phloem, whose termini consists of rowsof slender cells. These sieve-like cells are surrounded by moreor less isodiametrical sheath cells with dimensions similarto the secretory cells. Details of nectary functioning are basedon enhanced structural information, complementary data on nectardischarge after experimental manipulations and the nature ofthe effluence.Copyright 1998 Annals of Botany Company Digitalis purpureaL.; foxglove; floral nectary; (ultra-)structure; 3-D reconstruction; morphometry; nectar flow; time-lapse video recording.     

Nectary structure and nectar characteristics in someBignoniaceae

The nectary structure and chemical nectar composition of 15 species belonging to 12 genera ofBignoniaceae are analyzed. All taxa bear a conspicuous nuptial nectary surrounding the ovary base. The secretory tissue is mostly supplied by phloem branches. The stomata are located in the middle and upper part of the nectary epidermis with an homogeneous distribution. The nuptial nectary is proportionally large in relation to the ovary (15–30%), disregarding the nectary volume. Most species have extranuptial nectaries in both inner and outer surfaces of the calyx. Both kinds of nectaries lack a vascular tissue that straightly supplies them. Nuptial nectar concentration (wt/wt) ranges from 19 to 68%. Sugars and amino acids are found in all species. Half of the species have hexose predominant nectars, the remaining sucrose predominant. Phenols are detected in only three species, whereas reducing acids exclusively inTecoma stans. Alkaloids and lipids were never detected. Extranuptial nectar chemical composition is analyzed in two species:Dolichandra cynanchoides andPodranea ricasoliana. Bees constitute the main flower visitors of the species studied whereas hummingbirds were seen visiting three species. A correlation analysis is performed with the data obtained. There are a few significant correlations which indicate a parallel increase of three parameters: the longer the flower length, the more voluminous the nectary and the higher stomata number, independently of the floral biotype. Phenograms are obtained using 24 floral characters including nectary and nectar data. The clusters obtained do not reflect taxonomic relationships but are useful in the understanding of animal-plant interactions when the flower biotype is considered.This paper is based on a chapter of a doctoral thesis presented at the University of Córdoba (Argentina).     

长药景天花蜜腺的发育解剖学研究

长药景天花蜜腺５枚,呈侧向扁平的舌形或弯月形,分别位于５株离生心皮的外侧,两者的基部相连,属于子房蜜腺。蜜腺由分泌表皮、产蜜组织和仅含韧皮部的维管束组成。长药景天花蜜腺起源于心皮外侧基部的表层结构。产蜜组织在发育过程中,细胞中的液泡体积及淀粉粒呈现有规律的消长变化。泌蜜后期,蜜腺组织从上往下液泡化,具明显的方向性。根据其结构及多糖变化分析,来自韧皮部的原蜜汁以淀粉粒形式贮存于产蜜组织中,泌蜜期水解     

A new pollination system: brood-site pollination by flower bugs in Macaranga (Euphorbiaceae)

Background and Aims Macaranga: (Euphorbiaceae) is a large genus of dioecious trees with approx.260 species. To date, only one pollination study of the genushas reported brood-site pollination by thrips in M. hullettii.In this study, the pollination system of Macaranga tanariusis reported. Methods: The study was conducted on Okinawa and Amami Islands, Japan.Flower visitors on M. tanarius were collected and their pollenload and behaviour on the flowers examined, as well as inflorescencestructure and reward for the pollinators. Key Results: The most abundant flower visitors found on the male and femaleinflorescences were Orius atratus (Anthocoridae, Hemiptera),followed by Decomioides schneirlai (Miridae, Hemiptera). Pollenload on O. atratus from flowering pistillate inflorescenceswas detected as well as from staminate flowers. Orius atratusand D. schneirlai are likely to use the enclosed chambers formedby floral bracts as breeding sites before and during floweranthesis, and feed on nectar on the adaxial surface of flowerbracts. The extrafloral nectary has a ball-shaped structureand the contained nectar is not exposed; the hemipterans piercethe ball to suck out the nectar. Conclusions: The results indicate that the plant is pollinated by flowerbugs breeding on the inflorescences. This study may be the firstreport of pollination systems in which flower bugs are the mainpollinators. Similarity of pollination systems between M. hullettiiand M. tanarius indicates that the two brood-site pollinationsystems have the same origin. The pollinator species belongsto a predacious group, whose major prey includes thrips. Thepollination system might represent a unique example of evolutionfrom predatory flower visitors feeding on the pollinators (thrips)to the main pollinators.     

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.     

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

Background and Aims

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.

Methods

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.

Key Results

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.

Conclusions

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.Key words: Buckwheat, distyly, Fagopyrum esculentum, inflorescence position, morph comparisons, nectary histology, nectar sugar concentration, nectar volume, light intensity, organ biomass, phloem sap, plant age     

Floral nectary,nectar production dynamics,and floral reproductive isolation among closely related species of Pedicularis

Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis;however,few studies have examined variation of nectary structure and/or nectar secretion in the genus,particularly among closely related species. Here we investigated nectary morphology,nectar quality,and nectar production dynamics in flowers of Pedicularis section Cyathophora. We found a conical floral nectary at the base of the ovary in species of the rex-thamnophila clade. Stomata were found on the surface of the nectary,and copious starch grains were detected in the nectary tissues. In contrast,a semi-annular nectary was found in flowers of the species of the superba clade. Only a few starch grains were observed in tissues of the semi-annular nectary,and the nectar sugar concentration in these flowers was much lower than that in the flowers of the rexthamnophila clade. Our results indicate that the floral nectary has experienced considerable morphological,structural,and functional differentiation among closely related species of Pedicularis. This could have affected nectar production,leading to a shift of the pollination mode. Our results also imply that variation of the nectary morphology and nectar production may have played an important role in the speciation of sect. Cyathophora.     

Interpopulation variation in nectar production in Aconitum columbianum (Ranunculaceae)

Summary In Aconitum columbianum there are extreme interpopulation differences in rates of nectar secretion per flower. Since nectar sugar concentration varies little among populations, increased nectar secretion results in a greater mass of sugar per flower for pollinator attraction. These differences in the amount of reward offered per flower account at least in part for observed higher levels of pollinator activity in populations with high nectar production. Nectar production is correlated also with nectary depth, i.e., flowers in populations with deep nectaries have higher rates of nectar secretion than those with shallow nectaries. Nectary depth differences adapt populations to different pollinator-types. Populations with deeper nectaries are adapted to pollination by bumblebees with longer tongues and more specialized foraging behaviors. In conclusion, there are basic differences in pollination ecology among geographical races of a. columbianum, which are indicated by correlated interpopulution differences in (1) nectar production, (2) level of pollinator activity, (3) nectar depth, and (4) pollinator-type.