Scent glands in legume flowers

Variation in the Floral Scent Chemistry of Nymphaea 'Eldorado', a Valuable Water Lily, with Different Flowering Stages and Flower Parts

Nymphaea 'Eldorado', a valuable water lily, is a well-known fragrant plant in China. Studying the temporal and spatial characteristics of the floral components of this plant can provide a reference for the further development and utilization of water lily germplasm resources. In this study, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used to explore the types and relative contents of floral components at different flowering stages (S1: bud stage; S2: initial-flowering stage; S3: full-flowering stage; S4: end-flowering stage) and in different floral organs of N. 'Elidorado', combined with the observation of the microscopic structure of petals. A total of 60 volatile organic compounds (VOCs) were detected at different flowering stages, and there were significant differences in floral VOCs at different flowering stages and in different flower organs. The volatile compounds of N. 'Eldorado' can be divided into seven chemical classes,, namely, alkenes, alcohols, esters, aldehydes, ketones, alkanes, and others; the most common were alkenes and alkanes. A total of 39, 44, 47, and 42 volatile compounds were detected at S1, S2, S3, and S4. The VOCs present in high concentrations include benzaldehyde, benzyl alcohol, benzyl acetate, trans-α-bergamotene, α-curcumene, cis-α-farnesene, and so on. The types and total contents of volatiles at the full-flowering stage were higher than at other flowering stages. Comparing the VOCs in different parts of flower organs, it was found that the contents of alcohols, esters, and aldehydes were greatest in the petals, the alkenes in stamens were abundant with a relative content of up to 54.93%, and alkanes in the pistil were higher than in other parts. The types and total contents of volatiles in the stamens of N. 'Eldorado' were higher than those in other flower organs; they were the main part releasing fragrance. The observation of petal microstructure revealed that the size and quantity of the papillae on the epidermises of petals, the number of intracellular plastids, and the aggregates of floral components (osmophilic matrix granules) were significantly higher at the full-flowering stage than at the other flowering stages. This study suggested the main flowering stage and location at which the floral VOCs are released by N. 'Eldorado' and provided a reference for guiding the breeding of this water lily, exploring genetic patterns and developing related products.

Unveiling foliar secreting sites and secretion composition in the legume tree Swartzia flaemingii Raddi

Secretory structures in plants play a crucial role in producing bioactive compounds. Despite the potential of the Swartzia genus, comprehensive studies in this context are still scarce. Swartzia is a legume tree (Fabaceae) that occurs in the Brazilian Atlantic Forest, a biodiversity hotspot, and includes species such as Swartzia flaemingii. Therefore, we aim to achieve: (1) identify and characterize the key secretory sites responsible for saponin production in S. flaemingii leaflets; (2) confirm the presence of saponins in S. flaemingii leaves by comparing them with known chemical profiles of other Swartzia species; (3) assess the potential hemolytic and cytotoxic effects of crude leaf extracts. Our investigation unveils the presence of phenolic idioblasts, mucilage cells, and articulate laticifers, which play pivotal roles in defense and adaptation. Notably, we report the first-ever ultrastructural details of laticifers in a legume species. Additionally, oleanane-type saponins were identified in the leaves, giving insights into the chemotaxonomic profile of Swartzia. The crude extracts show low cytotoxicity levels, showcasing as a promising alternative source of saponins. This investigation reinforces the importance of conserving plants in threatened regions like the Atlantic Forest, a global biodiversity hotspot facing substantial anthropogenic pressures.

Exploring the co-operativity of secretory structures for defense and pollination in flowering plants

MAIN CONCLUSION

In flowers multiple secretory systems cooperate to deliver specialized metabolites to support specific roles in defence and pollination. The collective roles of cell types, enzymes, and transporters are discussed. The interplay between reproductive strategies and defense mechanisms in flowering plants has long been recognized, with trade-offs between investment in defense and reproduction predicted. Glandular trichomes and secretory cavities or ducts, which are epidermal and internal structures, play a pivotal role in the secretion, accumulation, and transport of specialized secondary metabolites, and contribute significantly to defense and pollination. Recent investigations have revealed an intricate connection between these two structures, whereby specialized volatile and non-volatile metabolites are exchanged, collectively shaping their respective ecological functions. However, a comprehensive understanding of this profound integration remains largely elusive. In this review, we explore the secretory systems and associated secondary metabolism primarily in Asteraceous species to propose potential shared mechanisms facilitating the directional translocation of these metabolites to diverse destinations. We summarize recent advances in our understanding of the cooperativity between epidermal and internal secretory structures in the biosynthesis, secretion, accumulation, and emission of terpenes, providing specific well-documented examples from pyrethrum (Tanacetum cinerariifolium). Pyrethrum is renowned for its natural pyrethrin insecticides, which accumulate in the flower head, and more recently, for emitting an aphid alarm pheromone. These examples highlight the diverse specializations of secondary metabolism in pyrethrum and raise intriguing questions regarding the regulation of production and translocation of these compounds within and between its various epidermal and internal secretory systems, spanning multiple tissues, to serve distinct ecological purposes. By discussing the cooperative nature of secretory structures in flowering plants, this review sheds light on the intricate mechanisms underlying the ecological roles of terpenes in defense and pollination.

Colleters, osmophores, and nectaries in the species Ceropegia lenewtonii: a sapromyiophilous stapeliad (Asclepiadoideae, Apocynaceae)

Ceropegia lenewtonii (Plowes) Bruyns (=Huernia keniensis), currently belonging to the Huernia section of the genus Ceropegia, is a stapeliad species distributed in Africa and the Arabian Peninsula; but it is widely cultivated as ornamental in most parts of the world. This species of stapeliad presents "carrion flowers" associated with a sapromyophilous pollination syndrome since the flowers emit an unpleasant odor. In this work, we describe the floral morphology and anatomy of the calyx, corolla, and corona of this species based on bright-field and scanning electron microscope techniques. We detected the presence of diverse floral secretor tissues, and based on different histochemical tests, the principal component of the secreted substance was identified. We interpret the functions of the glands and compare with other related species of stapeliads. Our results indicate that flowers of C. lenewtonii present colleters in sepals, osmophores in corolla, and primary and secondary nectaries in corona. All these floral glands have specific functions that involve the processes of pollination and reproduction of this species, as well as protection and defense mechanisms.

Osmophores and petal surface traits in Bignonieae species

This study characterizes the osmophores and corolla traits in 18 species of Bignonieae Dumort., a Bignoniaceae tribe occurring in the Cerrado, a neotropical savanna in Brazil. To detect osmophore distribution, whole, newly opened flowers were immersed in Neutral Red Solution. Samples from the corolla tube and lobes were also fixed and analyzed micromorphologically, anatomically, and histochemically. The osmophores showed six markedly different distribution patterns that were not clearly associated with histological features. In most species, osmophores comprised papillose secretory epidermises and a few layers of subepidermal parenchyma. Starch grains, lipid droplets, and terpenes were detected in osmophores. An ornamented cuticle, cuticular folds, glandular and non-glandular trichomes, raised stomata and epicuticular wax granules are common traits in the species studied and may be useful in determining the taxonomy of the group. We found that 94% of the species visited by bees had papillose epidermises while the single hummingbird-pollinated species presented a flattened epidermis. Variations in osmophore pattern among species visited by bees, including variations within the same plant genus, are novel finding. Additionally, the Bignonieae species visited by bees presented a textured corolla surface, which has been reported as facilitating bee attachment and movement towards the floral resource. Future studies with a greater number of Bignonieae species and more detailed pollinator behavioral assays may help in the interpretation of the variations in corolla traits and functional relationships between flowers and pollinators.

Are the floral morphology and anatomy of Galphimia australis, an atypical neotropical Malpighiaceae, associated to a new pollination syndrome?

The flowers of the species of Malpighiaceae in the Neotropical Region are relatively uniform in their morphology due to their dependence on oil-collecting bees as their main pollinators. However, many species of the genus Galphimia seem to have acquired a different floral syndrome, lacking markedly zygomorphic flowers and developed elaiophores in the calyx. Likewise, these species present anthers with great development, probably in response to the selection of pollinators that collect pollen. Galphimia australis incorporated some of these traits but also retained some residual characteristics typical of species pollinated by oil bees. This leads to many questions on how these flowers ensure their pollination. Inquiring about the reduction or modification of these characteristics allows us to understand how G. australis achieves a different pollination syndrome. In this research, we carry out a detailed morphological and anatomical study of the flowers and pollen grain devolvement of G. australis and floral visitors were observed and captured. Results were analyzed in order to determine how this species changed from the oil-floral syndrome, typical of neotropical Malpighiaceae, to one syndrome with pollen as the main reward.

The roles of the ostiole in the fig-fig wasp mutualism from a morpho-anatomical perspective

The syconium is the urn-shaped inflorescence shared by all species of the genus Ficus. The orifice at the apex of the syconium is called the ostiole, and it is covered by interlocking bracts. The ostiolar bracts can have different arrangements, which only allow the entry of mutualist wasps and promote reproductive isolation among Ficus species. Here, we analyze the ostiolar structures that could play a role as selective filter and therefore impact the fig-fig wasp mutualism in the neotropical Ficus sections Americanae and Pharmacosycea. Samples of syconia with pistillate flowers during the receptive phase of seven species of Ficus were examined using light and scanning electron microscopy. Tests for histolocalization of substances were employed to detect secretory activity throughout the ostiolar tissues. Our results indicated that the ostiole has two components: ostiolar bracts and the periostiolar zone. Interspecies variation in ostiolar bract arrangement in both sections studied was broader than previously reported. We report for the first time for Ficus: (i) two types of ostiolar osmophores (mesophyll and diffuse), that could be a source of volatile compounds for attracting fig wasps; (ii) colleters in the axil of ostiolar bracts, which probably lubricate and facilitate the entry of pollinating wasps into the syconial cavity; (iii) secretory trichomes around the ostiolar bracts, and (iv) syconium basal bracts (F. isophlebia) covering the ostiole, which are the first physical barrier that the fig wasps must overcome to access receptive pistillate flowers. We describe the zones that compose the ostiole, which support the hypothesis that the ostiole is a selective filter in the interactions of fig trees with Agaonidae fig wasps. We also suggest that ostiolar osmophores, colleters, the periostiolar zone, and the arrangements of the ostiolar bracts may be informative with respect to Ficus systematics.

Comparative Study of the Petal Structure and Fragrance Components of the Nymphaea hybrid, a Precious Water Lily

Nymphaea hybrid, a precious water lily, is a widely-cultivated aquatic flower with high ornamental, economic, medicinal, and ecological value; it blooms recurrently and emits a strong fragrance. In the present study, in order to understand the volatile components of N. hybrid and its relationship with petals structure characteristics, the morphologies and anatomical structures of the flower petals of N. hybrid were investigated, and volatile compounds emitted from the petals were identified. Scanning and transmission electron microscopy were used to describe petal structures, and the volatile constituents were collected using headspace solid-phase microextraction (HS-SPME) fibers and analyzed using gas chromatography coupled with mass spectrometry (GC-MS). The results indicated that the density and degree of protrusion and the number of plastids and osmiophilic matrix granules in the petals play key roles in emitting the fragrance. There were distinct differences in the components and relative contents of volatile compounds among the different strains of N. hybrid. In total, 29, 34, 39, and 43 volatile compounds were detected in the cut flower petals of the blue-purple type (Nh-1), pink type (Nh-2), yellow type (Nh-3) and white type (Nh-4) of N. hybrid at the flowering stage, with total relative contents of 96.78%, 97.64%, 98.56%, and 96.15%, respectively. Analyses of these volatile components indicated that alkenes, alcohols, and alkanes were the three major types of volatile components in the flower petals of N. hybrid. The predominant volatile compounds were benzyl alcohol, pentadecane, trans-α-bergamotene, (E)-β-farnesene, and (6E,9E)-6,9-heptadecadiene, and some of these volatile compounds were terpenes, which varied among the different strains. Moreover, on the basis of hierarchical cluster analysis (HCA) and principal component analysis (PCA), the N. hybrid samples were divided into four groups: alcohols were the most important volatile compounds for Nh-4 samples; esters and aldehydes were the predominant volatiles in Nh-3 samples; and ketones and alkenes were important for Nh-2 samples. These compounds contribute to the unique flavors and aromas of the four strains of N. hybrid.

Anatomy and ultrastructure floral osmophores of Catasetum fimbriatum (Orchidaceae)

Catasetum fimbriatum is a dioecious species whose flowers fully adapted to an euglossinophilic mode of pollination. Euglossini male bees collect the volatile fragrances which are produced in osmophores on the flowers. In order to understand the mechanism of scent secretion and floral interaction with the pollinator, we describe the location, histochemistry, anatomy, and ultrastructure of osmophores in pistillate and staminate flowers of this species. Fresh flowers were submerged in neutral red solution to locate the position of the osmophores. Other histochemical test performed includes the NADI reaction to detect terpenoids, Sudan IV for lipids, and Lugol's iodine solution to detect starch. Anatomical and ultrastructural traits were studied with bright field and transmission electron microscopes, respectively. The location of osmophores differs between pistillate and staminate flowers. In pistillate flowers, secretory tissues were observed on the ribbed adaxial surface of the labellum, but not on its margins, whereas in staminate flowers, they were found throughout the adaxial surface of the labellum and especially in the fimbriae. Anatomy and ultrastructure of the osmophores in the labellum of both types of flowers were similar. They present characteristics of metabolically active cells, such as abundant mitochondria, rough endoplasmic reticulum, vesicles, plastids with starch grains, and lipid globules. Granulocrine secretion and cycles of cytoplasmic contraction and expansion appear to allow the release of products without involving the rupture of the cuticle. Individuals of Eufriesea auriceps and Euglossa sp. were captured in staminate and pistillate flowers but, it seems likely, that only the former pollinates this orchid species.

Resolving the non-papilionaceous flower of Camoensia scandens, a papilionoid legume of the core genistoid clade: development, glands and insights into the pollination and systematics of the group

Camoensia scandens is a papilionoid legume inserted in the core genistoid clade. It has large, crepuscular, scented flowers but the corolla is non-papilionaceous, which deviates from the pattern found in the subfamily. The vexillum has a folded claw, forming a tube, which is opposed to the androecium opening; all petals have yellow-gold crinkled margins. In addition, there is a long hypanthium, which stores a translucid liquid. The goal of this study is to elucidate the ontogenetic pathways that result in such a peculiar flower and the glands responsible for the sweet fragrance of the petals. Floral buds and flowers were processed for SEM, TEM and light microscopy analyses. Five sepals arise unidirectionally followed by five petals that initiate simultaneously. After the petals, 11 stamens emerge unidirectionally; a pair of adaxial stamens is opposite to the vexillum. In the intermediate developmental stages the sepals unite basally; the two adaxial sepals unite with each other to a greater extent than with the other sepals. The filaments are basally connate, forming a tube with an adaxial opening at the base. The carpel emerges concomitantly with the two abaxial antepetalous stamens. The long hypanthium forms from the outer floral organs (base of the sepals, petals, filaments) and is attached to the base of the stipe. The corolla is noticeable in the intermediate stages of development. The crinkled golden margins house scent glands formed of a secretory epidermis with secretory trichomes and secretory subepidermal cells. The odor is composed of neutral polysaccharides, nitrogenous substances and essential oils. An extensive nectariferous region is found on the inner surface of the hypanthial tube. The nectar is translucent, viscous and released through large pores. The comparison of our data with that of other genistoid flowers enabled discussions about the pollination and systematics of the group.

Localization, morphology, anatomy and ultrastructure of osmophores in species of Rhamnaceae

Although the presence of scent was described for several species of Rhamnaceae, localization, morphology and structure of osmophores were unknown. We studied different species of the tribes Rhamneae (Rhamnoids clade), Pomaderreae, Colletieae, Paliureae (Ziziphoids clade) and the species Alphitonia excelsa (unknown tribe, Ziziphoids clade). We expect to have a better comprehension of these structures and provide information on which morphological and anatomical characters may support the phylogeny of the family. We localized the osmophores in the margins and top of the sepals using neutral red. Histochemical tests were made on transverse hand-cut sections of fresh sepals. Observations were made with stereoscopic and bright field microscopes, scanning and transmission electron microscopes. Papillae were observed in the zones with positive reaction to reagents. Different kinds of hairs are present in the sepal epidermis besides papillae. Epidermal cells present a striate cuticle with canals and cavities. Druses are abundant in most species. The ultrastructure of epidermal and subepidermal cells shows high metabolic activity: there are vesicles, mitochondria, endoplasmic reticulum, dictyosomes, plastids with lipids and starch. The vascularization is well developed and reaches the top of the sepal where the principal area of volatile components production is localized. The location and abundance of papillae are the most important traits that allow us recognize and characterize the osmophores in Rhamnaceae. There are no clear anatomical and morphological features exclusive of one clade or tribe. Therefore, in contrast to other sporophytic structures of this family, osmophores do not seem to have any systematic value.

Unravelling the structure and function of the petal appendages in the tribe Schwenckieae (Solanaceae)

The tribe Schwenckieae (Solanaceae) is characterised by the presence of appendages on the corolla, a diagnostic trait for the group. These appendages constitute a median distal projection of the three-lobed petal and occur in the genera Melananthus and Schwenckia but are absent in Heteranthia. We investigated the micromorphology and anatomical structure of the appendages and lateral petal lobes of Schwenckia americana (two varieties), S. angustifolia, S. curviflora and S. novaveneciana, and Melananthus fasciculatus. We also performed histochemical tests to determine if the appendages are involved in the production of volatiles, acting as a fragrance secretory structure (osmophore). The appendages have a uniseriate epidermis, whose cells store phenolics and lipids. The parenchyma is starch-rich just prior to anthesis in all species studied. The sensory test and anatomical analyses identified scent-secreting tissues, not only in the appendages, but also in the lateral petal lobes, whose cells are papillose with a sculptured surface. The α-naphthol p-phenylenediamine (NADI) reaction detected volatile (essential oils) compounds in S. americana var. americana and S. americana var. angustifolia. We demonstrated the secretory tissues and the production of lipids in the corolla appendages of Schwenckia and Melananthus, which indicate their osmogenic function and probable scent emission to attract pollinators.

Comparative analyses of cuticular waxes on various organs of faba bean (Vicia faba L.)

Cuticular waxes cover the plant surface and serve as hydrophobic layer, exhibiting various wax profiles between plant species and plant organs. This paper reports comprehensive analysis of the waxes on organs exposed to air, including leaf, stem, pod pericarp, and petals (banner, wing and keel), and on seed coat enwrapped in pod pericarp of faba bean (Vicia faba). In total 7 classes of wax compounds were identified, including fatty acids, primary alcohols, alkyl esters, aldehydes, alkanes, cinnamyl alcohol esters, and alkylresorcinols. Overall, primary alcohols dominated the waxes on leaves and the seed coat enwrapped in pod pericarp, alkanes accumulated largely in stem and petals, whereas alkylresorcinols were observed in leaf, stem and pod pericarp. Organs exposed to air had higher coverage (>1.2 μg/cm²) than those on seed coat (<0.8 μg/cm²), and keel having the highest wax coverage. Meanwhile, the wax coverage on seed coat reduced during the seed development. The variations of wax coverages, compound class distributions and chain length profiles among organs suggested that wax depositions were associated with their ecophysiological functions, and the enzymes involved in wax biosynthesis also showed organ-specific.

Osmophores and floral fragrance in Anacardium humile and Mangifera indica (Anacardiaceae): an overlooked secretory structure in Sapindales

Flowers of Anacardiaceae and other Sapindales typically produce nectar, but scent, often associated with a reward for pollinators, has surprisingly been mentioned only rarely for members of the family and order. However, flowers of Anacardium humile and Mangifera indica produce a strong sweet scent. The origin and composition of these floral scents is the subject of this study. Screening of potential osmophores on the petals and investigations of their anatomy were carried out by light, scanning and transmission electron microscopy. The composition of the floral fragrance was characterized by gas chromatography-mass spectrometry. In both species, the base of the adaxial side of each petal revealed specialized secretory epidermal cells which are essentially similar in structure and distinct from all other neighbouring cells. These cells also showed evidence of granulocrine secretory mechanisms and slight specific variations in their subcellular apparatus coinciding with the respective composition of the floral fragrance, predominantly composed of sesquiterpenes in A. humile and monoterpenes in M. indica. This study reports the presence of osmophores for the first time in flowers of Anacardiaceae and confirms the link between the ultrastructural features of their secretory cells and the volatiles produced by the flowers. The flowers of most Sapindales, including Anacardiaceae, are nectariferous. However, the presence of osmophores has only been described for very few genera of Rutaceae and Sapindaceae. Both the occurrence of osmophores and fragrance may have largely been overlooked in Anacardiaceae and Sapindales until now. Further studies are needed to better understand the nature and diversity of the interactions of their nectariferous flowers with their pollinators.

On the bioherbicide potential of Ulex europaeus and Cytisus scoparius: Profiles of volatile organic compounds and their phytotoxic effects

The phytotoxic potential of the legume shrubs Ulex europaeus L. (gorse) and Cytisus scoparius (L.) Link. (Scotch broom) is studied in this work for the first time. On the basis of their richness in active principles, the previous evidence of biological activity, and the abundance of biomass in their native range and invaded areas, a question arose: can U. europaeus and C. scoparius be considered as potential sources of natural herbicides for sustainable agriculture? By means of volatile bioassays, the flowering fresh plant material of both shrub species was shown to produce and emit volatile organic compounds (VOCs) able to inhibit the germination and/or early growth of two agricultural weeds: Amaranthus retroflexus and Digitaria sanguinalis. Novel complete VOCs profiles from the volatile extracts of the shrub species were obtained by GC and GC/MS. A total of 20 compounds were identified from U. europaeus flowering biomass, theaspirane and eugenol, among others, being described in gorse for the first instance. The chemical profile of C. scoparius yielded 28 compounds and was rich in oxygenated monoterpenes such as terpinen-4-ol, verbenol, α-terpineol, and verbenone, which were also identified in this species for the first time. Using dose-response bioassays with pure compounds, these VOCs were argued to be involved in the phytotoxicity observed for the plant materials, even at very low concentrations. The phytotoxic effects were predominantly irreversible, particularly for D. sanguinalis, since the seeds exposed to the VOCs produced damaged seedlings, were unable to recover germination capacity after removing the phytotoxin or, when recovered, produced unviable seedlings. Our results extend the interest of the abundant U. europaeus and C. scoparius for the obtention of natural products with bioherbicide potential, or to be used as allelopathic biomass in the development of new sustainable agricultural practices.

Disentangling historical signal and pollinator selection on the micromorphology of flowers: an example from the floral epidermis of the Nymphaeaceae

The family Nymphaeaceae includes most of the diversity among the ANA-grade angiosperms. Among the species of this family, floral structures and pollination strategies vary. The genus Victoria, as well as subgenera Lotos and Hydrocallis in Nymphaea, present night-blooming, scented flowers pollinated by scarab beetles. Such similar pollination strategies have led to macromorphological similarities among the flowers of these species, which could be interpreted as homologies or convergences based on different phylogenetic hypotheses about the relationships of these groups. We employed scanning electron microscopy of floral epidermis for seven species of the Nymphaeaceae with contrasting pollination biology to identify the main characters of the floral organs and the potential homologous nature of the structures involved in pollinator attraction. Moreover, we used transmission electron microscopy to observe ultrastructure of papillate-conical epidermis in the stamen of Victoria cruziana. We then tested the phylogenetic or ecological distribution of these traits using both consensus network approaches and ancestral state reconstruction on fixed phylogenies. Our results show that the night-blooming flowers present different specialisations in their epidermis, with V. cruziana presenting the most elaborate floral anatomy. We also identify for the first time the presence of conical-papillate cells in the order Nymphaeales. The epidermal characters tend to reflect phylogenetic relationships more than convergence due to pollinator selection. These results point to an independent and parallel evolution of scarab pollination in Nymphaeaceae and demonstrate the promise of floral anatomy as a phylogenetic marker. Moreover, they indicate a degree of sophistication in the anatomical basis of cantharophilous flowers in the Nymphaeales that diverges from the most simplistic views of floral evolution in the angiosperms.

Functional anatomy reveals secretory activity in papillose anthers of a buzz-pollinated Solanum species (Cyphomandra clade - Solanaceae)

Pollination in Solanum (Solanaceae) species is commonly performed by female bees, which vibrate anthers to extract pollen. Another pollen removal type is by male euglossine bees, milking the anthers when searching for floral scents produced by secretory tissues (osmophorous) at the swollen connective of the anthers of species in the Cyphomandra clade. Some species of this clade, however, are buzz-pollinated and present papillate anthers that should also have secretory activity, a hypothesis here tested. The anthers of Solanum luridifuscescens were fixed at different stages of development and analysed under light microscopy, SEM and TEM. Histochemical tests for the detection of starch and lipids were done. Epidermal cells of the abaxial surface of the anthers were visibly papillose, had large nuclei and dense cytoplasm rich in organelles such as mitochondria and plastids, typical features of secretory tissues. In this site, lipid droplets were detected, concomitantly with starch consumption, compatible with the secretory process in osmophores. No exudate or accumulation of substances was seen on the surface; in agreement with a previous pollination study performed in field conditions, where no pollinators were observed collecting floral scents, only pollen. The histochemical and structural analyses have evidenced the lipidic composition of the secretion, strongly pointing to terpenes as the secreted compounds. Ours findings show that papillae of the anthers have secretory activities that produce lipophilic compounds. This does not result in resources for bees, but could be an evolutionary step to the development of more specialised anthers in the Cyphomandra clade.

Petal micromorphology and its relationship to pollination

The characteristics of petal epidermal conical cells affect the quality of the signals perceived by various pollinators. This study aimed to identify variations in micromorphological characteristics of flower petals and their relationship to melittophily, ornithophily and chiropterophily pollination systems. The petals of 11 species were analysed using scanning electron microscopy and optical microscopy and the micromorphological traits were described, measured and compared using Tukey's test, PCA and cluster analysis. Unlike chiropterophily, all melittophilous and some ornithophilous species possessed adaxial epidermal conical cells. Cluster grouping separated chiropterophilous flowers from melittophilous and ornithophilous. PCA analysis showed that the two morphometric profile of conical cells was the attribute that most strongly influenced the grouping of species. When considering the data set of the three pollination systems, melittophilous and ornithophilous plants were more similar to each other than they were to chriopterophilous species. The distance between conical cell apices is an important parameter in interactions with pollinators. This study facilitated recognition of smoothing pollinator resource access through petal micromorphological characteristics. Further research regarding the biometry of micromorphological traits related to pollination is required.

Floral Volatiles in Parasitic Plants of the Orobanchaceae. Ecological and Taxonomic Implications

The holoparasitic broomrapes, Orobanche spp. and Phelipanche spp. (Orobanchaceae), are root parasites that completely depend on a host plant for survival and reproduction. There is considerable controversy on the taxonomy of this biologically and agronomically important family. Flowers of over 25 parasitic Orobanchaceae and a number of close, parasitic and non-parasitic, relatives emitted a complex blend of volatile organic compounds (VOCs), consisting of over 130 VOCs per species. Floral VOC blend-based phylogeny supported the known taxonomy in internal taxonomic grouping of genus and eliminated the uncertainty in some taxonomical groups. Moreover, phylogenetic analysis suggested separation of the broomrapes into two main groups parasitizing annual and perennial hosts, and for the annual hosts, into weedy and non-weedy broomrapes. We conclude that floral VOCs are a significant tool in species identification and possibly even in defining new species and can help to improve controversial taxonomy in the Orobanchaceae.

Flowers of the early-branching papilionoid legume Petaladenium urceoliferum display unique morphological and ontogenetic features

PREMISE OF THE STUDY

Floral development can help to shed light on puzzling features across flowering plants. The enigmatic Amazonian monospecific genus Petaladenium of the legume family (Leguminosae) had rarely been collected and only recently became available for ontogenetic studies. The fimbriate-glandular wing petals of P. urceoliferum are unique among the more than 19000 legume species. Ontogenetic data illuminate the systematic position of the genus and foster our understanding on floral evolution during the early diversification of the papilionoid legumes.

METHODS

Flower buds were collected in the field, fixed in 70% ethanol, and investigated using scanning electron microscopy (SEM). Results were compared with existing material from early-diverging papilionoid legumes.

KEY RESULTS

Formation of sepals and petals shows bidirectional tendencies. Stamens arise in two whorls, and the single carpel arises concomitantly with the outer stamen whorl. Gland formation starts early on the edges of the wing petals. The carpel reopens for a short time when the initiation of ovules is visible. Stomata at the base of the hypanthium indicate that the flower functions like other standard flag blossoms.

CONCLUSIONS

The floral ontogeny confirms the close affinity of P. urceoliferum with the florally heterogeneous, early-diverging papilionoid Amburaneae clade. The results strengthen the theory of a distinct experimental phase among early-branching papilionoid legumes during which a wider range of floral morphologies arose. Polysymmetry, monosymmetry, variable organ numbers, and a wide range of ontogenetic patterns laid the foundation for a successful canalization toward the more restricted but well-adapted dorsiventral papilionoid flag blossom.

Diversity of fig glands is associated with nursery mutualism in fig trees

PREMISE OF THE STUDY

Fig trees (Moraceae) have remarkable enclosed inflorescences called figs or syconia. The flowers are pollinated by host-specific fig wasps that enter the fig to lay their eggs. This nursery pollination system is one of the most studied of tropical mutualism interactions, but the source of the volatiles that attract fig wasps to their specific host figs has not been confirmed. The fragrance is the basis of host selection and, therefore, of reproductive isolation among sympatric Ficus species. This study locates and characterizes the glands likely to be responsible for pollinator attraction and also protection from herbivory in the figs of nine Ficus species representing all the major lineages within the genus.

METHODS

Figs with receptive pistillate flowers were examined using light and scanning electron microscopy. Tests for histolocalization of substances were employed to detect glandular activity throughout the figs.

KEY RESULTS

A great diversity of glands is found throughout the fig, and for the first time, the sites producing fragrances are identified. Scent glands are present on the ostiolar bracts and the outer layers of the fig receptacle. Laticifers and phenolic-producing idioblasts, epidermis, and trichomes associated with fig protection occur on the ostiolar bracts, the fig receptacle, and floral tissues.

CONCLUSIONS

The volatiles produced by glands on the ostiolar bracts are candidate sources for the long-distance attraction of pollinator fig wasps. Scent glands on the outer layers of the receptacle may also play a role in chemical perception of the figs or may be related to their protection. The high cost to the plants if the figs are eaten and the temperature conditions required for nursery pollination are likely the factors that led to the selection of phenolic glands and laticifers during the group's evolution.

Evidence for early intracellular accumulation of volatile compounds during spadix development in Arum italicum L. and preliminary data on some tropical Aroids

Staining and histochemistry of volatile organic compounds (VOCs) were performed at different inflorescence developmental stages on nine aroid species; one temperate, Arum italicum and eight tropical from the genera Caladium, Dieffenbachia and Philodendron. Moreover, a qualitative and quantitative analysis of VOCs constituting the scent of A. italicum, depending on the stage of development of inflorescences was also conducted. In all nine species, vesicles were observed in the conical cells of either the appendix or the stamens (thecae) and the staminodes. VOCs were localised in intracellular vesicles from the early stages of inflorescence development until their release during receptivity of gynoecium. This localisation was observed by the increase of both number and diameter of the vesicles during 1 week before receptivity. Afterwards, vesicles were fewer and smaller but rarely absent. In A. italicum, staining and gas chromatography analyses confirmed that the vesicles contained terpenes. The quantitatively most important ones were the sesquiterpenes, but monoterpenes were not negligible. Indeed, the quantities of terpenes matched the vesicles' size evolution during 1 week. Furthermore, VOCs from different biosynthetic pathways (sesquiterpenes and alkanes) were at their maximum quantity 2 days before gynoecium receptivity (sesquiterpenes and alkanes) or during receptivity (isobutylamine, monoterpenes, skatole and p-cresol). VOCs seemed to be emitted during gynoecium receptivity and/or during thermogenesis, and FADs are accumulated after thermogenesis in the spadix. These complex dynamics of the different VOCs could indicate specialisation of some VOCs and cell machinery to attract pollinators on the one hand and to repulse/protect against phytophagous organisms and pathogens after pollination on the other hand.