Floral Secretory Tissue: Nectaries and Osmophores

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Cell Biology".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 18722

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Guest Editor
Department of Plant Cytology and Embryology, Faculty ofBiology, University of Gdańsk, Wita Stwosza 59, 80-308, Gdańsk, Poland
Interests: plant cell ultrastructure; plant cell biology, plant anatomy; secretory tissue: nectaries and osmophores; plant pollination biology; orchids
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Dear Colleagues, 

Due to pressure from pollinators, various floral structures and diverse pollination strategies are developed in flowers , including short- and long-distance attractants. 

Nectar is the most common food and short-distance attractant produced in floral or extrafloral nectaries. Nectaries can differ significantly, taking into account their morphology, anatomy, ultrastructure, topography, and secretory processes. The term “nectary” refers to the place where nectar is produced and the visible nectar is offered to pollinators, however the nectar production and its demonstration may not take place in the same location.  

The ingredients dissolved in nectar can include various compounds: mainly carbohydrates, amino acids, proteins, enzymes, ions, antioxidants, toxic constituents, and fragrant components. 

Fragrance is the long-distance attractant, which may be produced in peculiar odor glands (osmophores) or may be exuded by morphologically indistinguishable floral tissues. In orchids, osmophores can form structures called “antennae”, which are swollen, prolonged apices of perianth petals. In some species, two heterogenic scent centers in one flower have been described. Fragrances are released periodically and are not accumulated on the epidermal surface, because of their cytotoxic nature. 

In this Special Issue, articles (original research papers, perspectives, opinions, reviews, methods) that focus on the biodiversity and function of the secretory tissue of nectaries and osmophores at all levels of research, including cell biology, molecular biology, biochemistry of nectar and fragrance, physiology, and ecology (field observations of pollination mechanisms), are most welcome. 

Dr. Agnieszka Kowalkowska
Guest Editor

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Keywords

  • chemical composition of fragrance
  • chemical composition of nectar
  • fragrance
  • nectar
  • nectary
  • osmophore
  • pollination strategy
  • pollinators
  • secretory process
  • transport of secretions
  • ultrastructure of secretory tissue

Published Papers (8 papers)

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Research

15 pages, 3896 KiB  
Article
Labellum Features and Chemical Composition of Floral Scent in Bulbophyllum carunculatum Garay, Hamer & Siegrist (Section Lepidorhiza Schltr., Bulbophyllinae Schltr., Orchidaceae Juss.)
by Natalia Wiśniewska, Marek Gołębiowski and Agnieszka K. Kowalkowska
Plants 2023, 12(7), 1568; https://doi.org/10.3390/plants12071568 - 06 Apr 2023
Viewed by 1411
Abstract
The vast majority of fly-pollinated Bulbophyllum species use a combination of visual and olfactory clues to mimic food sources and brood/oviposition sites of pollinators. The aims of the present work were to characterize the floral secretory tissue and the floral scent and compare [...] Read more.
The vast majority of fly-pollinated Bulbophyllum species use a combination of visual and olfactory clues to mimic food sources and brood/oviposition sites of pollinators. The aims of the present work were to characterize the floral secretory tissue and the floral scent and compare them with those previously described in B. echinolabium. Based on the histochemical results, the labellar secretion in B. carunculatum is the protein-rich mucilage. The adaxial epidermal cells of the labellum showed typical features of secretory activity. Plastids contained plastoglobuli, which are thought to be the places for scent production in osmophores. Juxtaposed with FeCl3 staining, the presence of dihydroxyphenolic globules in the cytoplasm of the epidermis and sub-epidermis was confirmed. Phenolic derivatives were also described with GC/MS analysis of the floral scent. The number of aromatic compounds and hydrocarbons was indicated in the floral scent of B. carunculatum. Moreover, pregnane-3,20-dione, occurring in the highest percentage in the floral fragrance of B. carunculatum, is a biologically active, 5-alpha-reduced metabolite of plasma progesterone. Progesterone is a mammalian gonadal hormone, but, like other steroid hormones, has been found in plants as intermediates in different biosynthetic pathways. The research on biosynthesis and functions of progesterone and its derivatives in flowers is still lacking. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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13 pages, 8729 KiB  
Article
Contrasting Pollination Strategies and Breeding Systems in Two Native Useful Cacti from Southern Brazil
by Rafael Becker, Oscar Perdomo Báez, Rosana Farias Singer and Rodrigo Bustos Singer
Plants 2023, 12(6), 1298; https://doi.org/10.3390/plants12061298 - 13 Mar 2023
Cited by 1 | Viewed by 1704
Abstract
Brazil is one of the centers of diversity of Cactaceae, yet studies addressing both pollination biology and the breeding system in Brazilian cacti are scarce. We herein present a detailed analysis of two native species with economic relevance: Cereus hildmannianus and Pereskia aculeata [...] Read more.
Brazil is one of the centers of diversity of Cactaceae, yet studies addressing both pollination biology and the breeding system in Brazilian cacti are scarce. We herein present a detailed analysis of two native species with economic relevance: Cereus hildmannianus and Pereskia aculeata. The first species produce edible, sweet, spineless fruits and the second species produces leaves with high protein content. Pollination studies were undertaken through fieldwork observations in three localities of Rio Grande do Sul, Brazil, over two flowering seasons, totaling over 130 observation hours. Breeding systems were elucidated utilizing controlled pollinations. Cereus hildmannianus is solely pollinated by nectar-gathering species of Sphingidae hawk moths. In contrast, the flowers of P. aculeata are pollinated by predominantly native Hymenoptera but also by Coleoptera and Diptera, which gather pollen and/or nectar. Both cacti species are pollinator-dependent; neither intact nor emasculated flowers turn into fruit, yet whereas C. hildmannianus is self-incompatible, P. aculeata is fully self-compatible. In sum, C. hildmannianus is more restrictive and specialized regarding its pollination and breeding system, whereas P. aculeata is more generalist. Understanding the pollination needs of these species is a necessary starting point towards their conservation but also for their proper management and eventual domestication. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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24 pages, 43339 KiB  
Article
Comparative Nectary Morphology across Cleomaceae (Brassicales)
by Brandi Zenchyzen, Stacie Weissner, Jaymie Martin, Ainsley Lopushinsky, Ida John, Ishnoor Nahal and Jocelyn C. Hall
Plants 2023, 12(6), 1263; https://doi.org/10.3390/plants12061263 - 10 Mar 2023
Viewed by 1712
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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16 pages, 6168 KiB  
Article
Labellar Structure of the Maxillaria splendens Alliance (Orchidaceae: Maxillariinae) Indicates Floral Polyphenols as a Reward for Stingless Bees
by Kevin L. Davies, Emerson R. Pansarin and Małgorzata Stpiczyńska
Plants 2023, 12(4), 921; https://doi.org/10.3390/plants12040921 - 17 Feb 2023
Cited by 1 | Viewed by 1371
Abstract
Several studies have reported stingless Meliponini bees gathering hairs from the labella of Maxillaria spp., including M. ochroleuca, a member of the M. splendens alliance. Such hairs usually contain food materials and are thought to have nutritional value. The papillose labella of [...] Read more.
Several studies have reported stingless Meliponini bees gathering hairs from the labella of Maxillaria spp., including M. ochroleuca, a member of the M. splendens alliance. Such hairs usually contain food materials and are thought to have nutritional value. The papillose labella of representatives of the Maxillaria splendens alliance, however, bear scattered, simple 1-5-celled uniseriate trichomes (hairs) that lack food materials. By contrast, here, as well as polyphenolic compounds, typical labellar papillae usually contain small quantities of starch, protein, and minute droplets of lipid, the last probably involved in the production of fragrance. Towards the labellum apex occur elevated groups of papillae that lack food materials, but contain volatile compounds, probably fragrance precursors. In the past, the terms ‘trichomes’ or ‘hairs’ and ‘papillae’ have been used interchangeably, causing some confusion. Since the trichomes, however, unlike the papillae, are easily detachable and can fragment, it is most likely they, not the papillae, that have previously been observed being collected by bees, but their poor food content indicates that they do not function as food-hairs. Even so, our field observations of M. ochroleuca reveal that stingless bees scrape polyphenol-rich labellar tissue and possibly use this material to produce a resinous, complex, heterogeneous substance commonly referred to as ‘bee glue’, used for nest construction and repair. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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12 pages, 3455 KiB  
Article
Pollination in Epidendrum densiflorum Hook. (Orchidaceae: Laeliinae): Fraudulent Trap-Flowers, Self-Incompatibility, and a Possible New Type of Mimicry
by Rodrigo Santtanna Silveira, Rodrigo Bustos Singer and Viviane Gianluppi Ferro
Plants 2023, 12(3), 679; https://doi.org/10.3390/plants12030679 - 03 Feb 2023
Cited by 1 | Viewed by 2338
Abstract
The pollination and the breeding system of Epidendrum densiflorum (Orchidaceae: Laeliinae) were studied through fieldwork and controlled pollinations in cultivated plants. Pollination is exclusively promoted by males of diurnal Lepidoptera: five species of Arctiinae and four of Ithomiinae were recorded as pollinators. These [...] Read more.
The pollination and the breeding system of Epidendrum densiflorum (Orchidaceae: Laeliinae) were studied through fieldwork and controlled pollinations in cultivated plants. Pollination is exclusively promoted by males of diurnal Lepidoptera: five species of Arctiinae and four of Ithomiinae were recorded as pollinators. These male insects are known to obtain alkaloids (through the nectar) in flowers of Asteraceae and Boraginaceae. However, the flowers of E. densiflorum are nectarless, despite presenting a cuniculus (a likely nectariferous cavity). Pollinators insert their proboscides into the flowers and remove or deposit the pollinaria while searching for nectar. The floral tube is very narrow, and insects struggle for up to 75 min to get rid of the flowers. Plants are pollinator-dependent and nearly fully self-incompatible. Pollinarium removal, pollination, and fruiting success (2.85%) were very low; facts that are consistent with the patterns globally observed in deceptive (rewardless) orchids. Nilsson’s male efficiency factor (0.245) was also low, indicating pollen loss in the system. Based on our field observations, we suggest that the fragrance of E. densiflorum likely mimics these plants that are normally used as a source of alkaloids by male Lepidoptera, a hypothesis that we intend to test in the future. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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16 pages, 3217 KiB  
Article
Variations in Structure among Androecia and Floral Nectaries in the Inverted Repeat-Lacking Clade (Leguminosae: Papilionoideae)
by Andrey Sinjushin, Maria Ploshinskaya, Ali Asghar Maassoumi, Mohammad Mahmoodi and Ali Bagheri
Plants 2022, 11(5), 649; https://doi.org/10.3390/plants11050649 - 27 Feb 2022
Cited by 1 | Viewed by 3667
Abstract
The vast majority of highly valuable species of the Leguminosae in temperate latitudes belong to the Inverted Repeat-Lacking Clade (IRLC). Despite having a generally conserved monosymmetric floral morphology, members of this group are remarkable with a pronounced diversity of floral sizes, modes of [...] Read more.
The vast majority of highly valuable species of the Leguminosae in temperate latitudes belong to the Inverted Repeat-Lacking Clade (IRLC). Despite having a generally conserved monosymmetric floral morphology, members of this group are remarkable with a pronounced diversity of floral sizes, modes of staminal fusion, and pollination strategies. This paper examined androecia and floral nectaries (FNs) in selected genera of the IRLC. External morphology was investigated using stereomicroscopy and scanning electron microscopy. In some cases, the pattern of staminal fusion was additionally examined in transverse sections using light microscopy. Androecia of all selected genera fell into one of four types, viz., monadelphous, pseudomonadelphous, diadelphous or diadelphous reduced (with inner stamens converted into sterile staminodes). However, there was significant variation in the stamens’ mode of contact, as well as the shape and size of the fenestrae providing access to FNs. Some types seemed to arise independently in different genera, thus providing a high level of homoplasy. FNs were more conserved and comprised areas of secretory stomata in the abaxial part of the receptacle and/or hypanthium. Nectariferous stomata could be found in very miniaturized flowers (Medicago lupulina) and could even accompany monadelphy (Galega). This indicates that preferential self-pollination may nevertheless require visitation by insects. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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11 pages, 4139 KiB  
Article
Examining the Role of Buzzing Time and Acoustics on Pollen Extraction of Solanum elaeagnifolium
by Mandeep Tayal and Rupesh Kariyat
Plants 2021, 10(12), 2592; https://doi.org/10.3390/plants10122592 - 26 Nov 2021
Cited by 5 | Viewed by 2033
Abstract
Buzz pollination is a specialized pollination syndrome that requires vibrational energy to extract concealed pollen grains from poricidal anthers. Although a large body of work has examined the ecology of buzz pollination, whether acoustic properties of buzz pollinators affect pollen extraction is less [...] Read more.
Buzz pollination is a specialized pollination syndrome that requires vibrational energy to extract concealed pollen grains from poricidal anthers. Although a large body of work has examined the ecology of buzz pollination, whether acoustic properties of buzz pollinators affect pollen extraction is less understood, especially in weeds and invasive species. We examined the pollination biology of Silverleaf nightshade (Solanum elaeagnifolium), a worldwide invasive weed, in its native range in the Lower Rio Grande Valley (LRGV) in south Texas. Over two years, we documented the floral visitors on S. elaeagnifolium, their acoustic parameters (buzzing amplitude, frequency, and duration of buzzing) and estimated the effects of the latter two factors on pollen extraction. We found five major bee genera: Exomalopsis, Halictus, Megachile, Bombus, and Xylocopa, as the most common floral visitors on S. elaeagnifolium in the LRGV. Bee genera varied in their duration of total buzzing time, duration of each visit, and mass. While we did not find any significant differences in buzzing frequency among different genera, an artificial pollen collection experiment using an electric toothbrush showed that the amount of pollen extracted is significantly affected by the duration of buzzing. We conclude that regardless of buzzing frequency, buzzing duration is the most critical factor in pollen removal in this species. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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19 pages, 1615 KiB  
Article
Floral Nectar Chemistry in Orchids: A Short Review and Meta-Analysis
by Emilia Brzosko and Paweł Mirski
Plants 2021, 10(11), 2315; https://doi.org/10.3390/plants10112315 - 27 Oct 2021
Cited by 10 | Viewed by 2846
Abstract
Nectar is one of the most important flower traits, shaping plant–pollinator interactions and reproductive success. Despite Orchidaceae including numerous nectariferous species, nectar chemistry in this family has been infrequently studied. Therefore, the aim of this study is to compile data about nectar attributes [...] Read more.
Nectar is one of the most important flower traits, shaping plant–pollinator interactions and reproductive success. Despite Orchidaceae including numerous nectariferous species, nectar chemistry in this family has been infrequently studied. Therefore, the aim of this study is to compile data about nectar attributes in different orchid species. The scarcity of data restricted analyses to sugar concentration and composition. Our results suggest that the most important factor shaping nectar traits in orchids is the pollinator type, although we also found differentiation of nectar traits according to geographical regions. In spurred orchids, the length of the spur impacted nectar traits. We recommend the development of studies on nectar chemistry in orchids, including a wider range of species (both in taxonomic and geographical contexts), as well as extending the analyses to other nectar components (such as amino acids and secondary metabolites). The nectar biome would be also worth investigating, since it could affect the chemical composition of nectar. This will enrich the understanding of the mechanisms of plants–pollinators interactions. Full article
(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)
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