Orbicule Morphology Research Articles

Systematic palynology in Korean Piperales with special focus on its exine surface ornamentation and orbicule morphology

The pollen and orbicule morphology of the Korean Piperales (Aristolochia, Asarum, Houttuynia, Piper, and Saururus) were investigated via scanning electron microscopy. Piperales pollen is a monad, its size ranging from very small to large (P = 7.78–51.4 μm, E = 6.68–43.1 μm), and having a mainly circular to sub-circular shape. The aperture type is constant in the genus [inaperturate (Aristolochia), tri to pentaporate (Asarum), and monosulcate (Houttuynia, Piper, and Saururus)]. There are four distinct types of exine ornamentation: Fossulate with perforate, microreticulate with gemmae, microperforate with granula, and microechinate. The orbicules (minute sporopollenin granules) were observed in all studied taxa and thus, may be a possible symplesiomorphic characteristic of Piperales. Further, the observed orbicule surface ornamentation was similar to pollen exine patterns, for example muri, gemmae, or granula. This resemblance between orbicule and pollen exine ornamentation may imply a similar biosynthesis pattern of sporopollenin of pollen exine and orbicules. The phenogram resulting from a cluster analysis using palynological characters was generally consistent with the known molecular phylogeny of Piperales. This initial study will help understand the palynological diversity and provide detailed information of pollen and orbicule characteristics in Piperales.

Could microechinate orbicules be related to the release of pollen in anemophilous and ‘buzz pollination' species?

The function of orbicules has been a matter of speculation for a long time and until now no satisfactory answer has been put forward. We propose two hypotheses that could contribute to the elucidation of their function: (1) that anemophilous and ‘buzz pollination’ species have microechinate orbicules; and (2) that microechinate orbicules are advantageous for pollen release in both pollination modes. To test the first hypothesis, orbicule morphology of species in which the pollen is released by anther shaking (20 anemophilous and three with buzz-pollination) was analysed. We also conducted a literature review, noting the orbicule surface type and the presence of floral traits suggesting that pollen is released by anther shaking. Ninety-two percent of the species with microechinate orbicules are anemophilous or present ‘buzz pollination’. Orbicules without spinules are present in species that lack floral traits linked to anther shaking for pollen release. To test the second hypothesis, a computational simulation that reveals the electric field produced by electrostatically charged orbicules was used. Results showed that the field is increased at the tip of each orbicule spinule. Therefore, an anther loculus surface coated by pointed structures increases the repulsion force of the pollen grains. This is an advantage when pollen is released by shaking the anther.

Systematic and morphologic survey of orbicules in allergenic angiosperms

Orbicules are sub- or pauci-micronic sporopollenin-coated particles associated with pollen grains. Recent studies have highlighted their importance in terms of systematic value or as vectors of allergens that may trigger pollinosis. While orbicules have indeed been reported for most families and genera of allergological importance, their usefulness in systematics remains little explored. Our study aims: (a) to discover the presence/absence of orbicules in species of allergological interest hitherto overlooked regarding these particles; (b) to propose standard descriptors for orbicule morphology; and (c) to link the features of orbicules to a systematic framework. We observed or measured selected orbicule traits in SEM micrographs of pollen sacs and pollen grains of 23 species of 17 genera in Asteraceae, Betulaceae, Fagaceae, Oleaceae, Poaceae, Plantaginaceae and Polygonaceae families. Categorical and continuous traits were included in a matrix and then subjected to NMDS as ordination method to assess the usefulness of orbicule traits as systematic characters. We detected orbicules both on the locule wall and on the pollen exine in almost all investigated species and described unknown nanoparticles smaller than orbicules. Based on orbicules traits, NMDS separated the samples at species level. We detected and described orbicules on the tapetum and on the pollen exine in 19 target species and observed unknown nanoparticles that might explain (a) the process of deposition of sporopollenin during orbicule development and (b) the onset of pollinosis before and after the dispersion of pollen grains into the air. Finally, within the restricted sample examined, selected orbicule traits allowed to resolve the data set at species level.

Pollen development and orbicule and pollen grain morphology in species of Cephalanthus (Rubiaceae-Naucleeae) from the Americas

This paper is the first embryological report on the genus Cephalanthus L. and contributes to future studies in other genera of the tribe Naucleeae. The development of the anther wall in Cephalanthus glabratus (Spreng.) K. Schum. corresponds to the dicot type and microsporogenesis is simultaneous. The young wall of the anther has four layers; epidermis, endothecium, one middle layer and the secretory tapetum. The tissue of the septum has idioblasts with crystalline sand. In the wall of the mature anther, only the endothecium and remnants of epidermal cells were preserved. The occurrence and morphology of orbicules were observed in the mature anthers of all three species of Cephalanthus with scanning electron microscopy. The orbicules have taxonomic value at species level, since these structures allow us to distinguish between the species analysed. The presence of a protruding oncus was observed for the first time in Cephalanthus in non-acetolysed pollen grains. According to our observations, this structure is not affected by the state of anther dehiscence in C. glabratus because the oncus is visible and prominent in the mature pollen grains in both indehiscent and dehiscent anthers.

Phylogenetic signal of orbicules at family level: Rubiaceae as case study

AbstractOrbicules are tiny a‐cellular sporopollenin structures that occur in the anthers of many angiosperms together with the pollen grains. Although their occurrence is common, little is known about their function and systematic usefulness. With regard to orbicules, Rubiaceae (Gentianales) are the most intensively studied plant family and therefore an ideal case to present the evolution and phylogenetic signal of orbicule characters at family level. The occurrence and morphology of orbicules was investigated in 64 species of Rubiaceae using scanning electron microscopy. Five relevant orbicule features (presence/absence, abundance, size, shape, ornamentation) were optimized onto a custom‐made phylogeny of the family. By optimizing the five orbicule characters some evolutionary trends can be observed. The previously suggested trend in angiosperms towards orbicule absence in more derived taxa is confirmed for Rubiaceae. Orbicules appear to have been independently lost at least nine times within the family, with two subsequent reversals. Small orbicules represent the plesiomorphic character state for the family. A trend from spherical towards irregular orbicules is observed, while ornamented orbicules occur only in derived lineages. Orbicule characters are constant at generic level and in most cases at tribal level, and therefore have potential for systematics. The presence of orbicules is correlated with the occurrence of a non‐amoeboid tapetum.

Palynological diversity and major evolutionary trends in Cyperaceae

Pollen and orbicule morphology of 84 species, representing 52 genera from all tribes and subfamilies are investigated, in order to assess the systematic value of palynological data and to determine palynological evolutionary trends in Cyperaceae. A total of 90% of the species are examined for the first time with scanning electron microscopy. Pollen grains of Cyperaceae are oblate spheroidal to perprolate in shape, inaperturate to polyporate with opercula or pontopercula on pori or colpi. We distinguished seven different sexine ornamentation patterns. Orbicules occur in all species investigated. Pollen morphological variation within Cyperaceae is considerable and includes dispersal unit; number, location and degree of differentiation of apertural zones; and sexine ornamentation patterns. In subfamily Mapanioideae both tribes can be characterized by palynological synapomorphies. However, in subfamily Cyperoideae, the observed pattern of variation does not fit the most recent molecular phylogeny due to high levels of homoplasy and polymorphism in major pollen characters.

Systematic palynology in Ebenaceae with focus on Ebenoideae: Morphological diversity and character evolution

This study examines the diversity and character transformations in pollen and orbicule morphology of Ebenaceae, with a focus on subfamily Ebenoideae (ca. 600 sp.). 62 specimens comprising all three genera of Ebenoideae ( Diospyos, Euclea, Royena), were studied using LM and SEM. Bayesian phylogenetic analysis was performed on molecular sequence data to establish an evolutionary hypothesis that was then used as an evolutionary framework to identify synapomorphies and trace evolutionary trends of palynological data with Bayesian posterior mapping and principle component analyses (PCA). Ebenoideae pollen is generally shed as monads (permanent tetrads in two species), medium-sized, prolate-spheroidal to subprolate and tricolporate. A substantial amount of variation is found in pollen size, equatorial outline (lobate, subtriangular, circular and hexagonal) and sexine ornamentation type ((micro)rugulate, striate, granulate and gemmate). Moreover, orbicules were present on the inner locule wall in all specimens examined. Their abundance, degree of fusion with tapetal membrane and aggregation vary considerably. We can conclude that Ebenaceae pollen is more heterogeneous than previously assumed. We traced palynological synapomorphies for groups at different taxonomic levels: subfamily level (pollen size, pollen wall stratification and aperture morphology), generic level (size, equatorial outline and sexine ornamentation types) and subgeneric clades (size, ectocolpus morphology, equatorial outline and sexine ornamentation subtypes) respectively. The granular infratectum and the unique sculpturing pattern on the orbicule walls are the most discriminating pollen features for subfamily Ebenoideae.

Systematic relevance of pollen and orbicule characters in the tribe Hillieae (Rubiaceae)

Pollen and orbicule morphology of 26 species in the tribe Hillieae is described based on observations by light, scanning and transmission electron microscopy. Pollen and orbicule characters are critically evaluated and discussed in the context of existing hypotheses of systematic relationships within the tribe. Pollen is 3-zonocolporate with a perforate, microreticulate, reticulate or eutectate sexine. In the two species of Blepharidium, however, the pollen has one, four or five apertures. These pollen morphological data were incorporated into an existing macromorphological matrix of the group and cladistically analysed. The resulting phylogenies indicate that it may be appropriate to reduce Cosmibuena to a subgenus of the genus Hillia, while Blepharidium should be removed from Hillieae because of the deviating pollen type that is unique to the Rubiaceae. All species investigated produce orbicules, which are mostly spherical and possess an electron-lucent core that is sometimes characteristically flattened.

Pollen morphology of Dioscorea (Dioscoreaceae) and its relation to systematics

This paper adds new data on the pollen and orbicule morphology of 61 Dioscorea L. (Dioscoreaceae) species to the survey of Schols et al. (2001). The results indicate that pollen characters may be significant in infrageneric systematics in Dioscorea. Pollen and orbicule characters are described based on observations with light microscopy, and scanning and transmission electron microscopy, and are critically evaluated and discussed in the context of existing hypotheses of systematic relationships within the genus. Pollen is mostly disulculate (sometimes monosulcate) with a perforate, microreticulate, striate, gemmate, rugulate, or cerebroid perforate sexine. The basal section Stenophora is one of the few sections with monosulcate pollen. Brachyandra, Cardiocapsa, and Seriflorae, three Malagasy sections, are characterized by striate pollen. Pollen morphology strongly supports section Enantiophyllum as a monophyletic group. The correlation between pollen size and tuber type, as suggested previously by P. Su (1987), is confirmed by our data. As found in our earlier survey, orbicules in Dioscorea are mostly spherical with a smooth or spinulose surface. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 375–390.

Morphology, ultrastructure and typology of orbicules in Loganiaceae s.l. and related genera, in relation to systematics

Minute granules of sporopollenin, called orbicules or Ubisch bodies, can be observed on the innermost tangential and/or radial walls of secretory tapetum cells. Orbicules were investigated with light microscopy as well as scanning electron, and transmission electron microscopy in 19 species of Loganiaceae s.l. and 32 related species. The species investigated cover all the recently recognised families segregated from Loganiaceae s.l.: Loganiaceae s.str., Gelsemiaceae, Geniostomaceae, Strychnaceae and Loganiaceae tribe Potalieae which is now included in the Gentianaceae. Orbicules were found in all the species of Loganiaceae s.l. that were investigated with the exception of Buddleja and Retzia. From the related species that were studied, 20 species (18 genera, seven families) possess orbicules. On the basis of observed morphological and ultrastructural variations, five orbicule types are described. The types are based on the orbicule typology previously described for the rubiaceous subfamilies Cinchonoideae and Ixoroideae. The systematic value of this typology is tested by comparison with the most recent classifications within Loganiaceae s.l. The heterogeneity of Loganiaceae s.l. is reflected in the variation of orbicule morphology. The two tribes Antonieae and Strychneae (Strychnaceae) are characterised by the presence of two very distinct types of orbicules (I or IIIa). In the most recent classifications of the Loganiaceae s.l. a relationship between Strychneae and the Loganiaceae s.str. (including Geniostomaceae) is suggested; this is confirmed by the presence of the same type of orbicules in all of these taxa. Gelsemiaceae species have one or other of two orbicule types (III or IV). The inclusion of the Loganiaceous tribe Potalieae in Gentianaceae is supported by the presence of the same orbicule type (V) as found in the genus Exacum and the former Loganiaceous genera Anthocleista and Fagraea now also included in Gentianaceae. In Apocynaceae s.l. orbicules do not occur in all tribes. Orbicules are present in the tribes Plumerioideae, Apocynoideae, and Periplocoideae (Asclepiadaceae). In the more derived genera of Asclepiadaceae (except Periplocoideae) orbicules do not occur. Results show that the systematic application of orbicule characteristics can be of value at the tribal level in the Loganiaceae s.l.

A survey of the presence and morphology of orbicules in European allergenic angiosperms. Background information for allergen research

Allergenic activity in the atmospheric aerosol of small particles in the size range of a few micrometres or less may play an important role in causing allergic reactions in the lower regions of the lungs, often seen in pollinosis. Orbicules (= Ubisch bodies) are small, mostly spherical granules of sporopollenin, which can occur on the radial and innermost tangential wall of secretory tapetum cells. In instances where orbicules of allergenic species are dispersed into the atmosphere, they may act as effective vectors of allergens. We investigated the presence and morphology of orbicules in 15 allergenic species using scanning electron microscopy. Orbicules were present in all species investigated of the families Betulaceae, Chenopodiaceae, Fagaceae, Poaceae, Polygonaceae, and Urticaceae. In the species of the Asteraceae and Oleaceae studied, orbicules were lacking. Almost all orbicules observed were spiny. Their mean diameters range from 0.342 to 1.130 μm. Orbicules can be part of the fraction of small particles in the size range of a few micrometres or less, emitted from the anthers. Our results clearly indicate that a thorough investigation of the sites of allergens across the whole anther is required to reveal whether or not these orbicules possess allergens.Key words: allergenic plants, allergen research, morphology, orbicules.

Morphology of pollen and orbicules in some Dioscorea species and its systematic implications

Pollen and orbicule morphology of 35 Dioscorea L. species is described based on observations with light microscopy, and scanning and transmission electron microscopy. Pollen and orbicule characters are critically evaluated and discussed in the context of existing hypotheses of systematic relationships within the genus. Pollen is mostly bisulcate (sometimes monosulcate) with a perforate, microreticulate or striate sexine. Our results indicate that pollen data may be significant at sectional rank. The close relationship between sections Asterotricha and Enantiophyllum proposed by Burkill and Ayensu is supported by pollen morphology as all species investigated share bisulcate, perforate pollen with small perforations and a high perforation density. Macromorphological differences between the two compound-leaved sectionsBotryosicyos and Lasiophyton are also supported by pollen morphology; pollens of these two sections have very different perforation patterns. Orbicules in Dioscorea are mostly spherical and possess a smooth or spinulose surface. The latter is often correlated with a striate sexine.

Morphology of pollen and orbicules in some Dioscorea species and its systematic implications

Pollen and orbicule morphology of 35 Dioscorea L. species is described based on observations with light microscopy, and scanning and transmission electron microscopy. Pollen and orbicule characters are critically evaluated and discussed in the context of existing hypotheses of systematic relationships within the genus. Pollen is mostly bisulcate (sometimes monosulcate) with a perforate, microreticulate or striate sexine. Our results indicate that pollen data may be significant at sectional rank. The close relationship between sections Astemtricha and Enantiophyllum proposed by I3urkill and Ayensu is supported by pollen morphology as all species investigated share bisulcate, perforate pollen with small perforations and a high perforation density. Macromorphological differences between the two compound-leaved sections Botryosicyos and Lasiophyton are also supported by pollen morphology; pollens of these two sections have very different perforation patterns. Orbicules in Dioscorea are mostly spherical and possess a smooth or spinulose surface. The latter is often correlated with a striate sexine. 0 2001 The Linnean Society of London

A survey of the presence and morphology of orbicules in European allergenic angiosperms. Background information for allergen research

A survey of the presence and morphology of orbicules in European allergenic angiosperms. Background information for allergen research

Pollen morphological support for the Catesbaeeae-Chiococceae-Exostema-complex (Rubiaceae)

The pollen morphology of the Catesbaeeae-Chiococceae-Exostema complex as recently treated by Delprete (1966) was examined with LM and SEM. The group is remarkably stenopalynous; typical representatives have medium sized, 3-colpate pollen with a perforate tectum covered with microspines. The inner nexine ornamentation is pronounced and offers more variation than the sexine pattern. A typology of the inside structures is presented based on LM observations and SEM observations of sectioned grains. Orbicules are common and numerous in the Catesbaeeae and Exostema-group; for most genera of the Chiococceae confirmation is needed of orbicule presence. All orbicules observed are relatively large (1-4 μm) and spiny. Pollen and orbicule morphology proved to be a powerful tool to delimit the Catesbaeeae-Chiococceae-Exostema complex. The overall delimitation of the complex is corroborated with our pollen data. The genera Mastixiodendron and Placocarpa, however, can be excluded from the complex based on their pollen morphology. Mastixiodendron has 3-colporate, perforate pollen without microspines and the endocolpi are fused into an endocingulum. Pollen of Placocarpa is reticulate and 3-colporate with perpendicular endocolpi.

Morphology and Taxonomic Application of Orbicules (Ubisch Bodies) in the GenusEuphorbia

El-Ghazaly, G. & Chaudhary, R. 1993. Morphology and taxonomic application of orbicules (Ubisch bodies) in the genus Euphorbia. – Grana Suppl. 2: 26–32. The orbicule morphology of some species of th...