Pollen dimorphism and anther culture in barley

Summary A dimorphism is observed in barley (Hordeum vulgare L., cv. Akka) pollen when stained with acetocarmine from the mid-binucleate stage onwards. The majority of grains have staining cytoplasms, while the remainder have cytoplasms which take up little or no stain (NS grains). The staining dimorphism cannot be detected at the late-uninucleate microspore stage when anthers are normally cultured, but the evidence suggests that the microspores have already diverged at this time and it is the cells destined to become NS grains in vivo that respond in culture to become pollen calluses. Evidence comes from a comparison of the frequencies of NS grains and pollen calluses and from their distribution between and within anthers.     

Major characters and enoplan systematics

The history of enoplan systematics is briefly reviewed. Various taxonomic characters significant at the generic level and above are discussed, with comments on their application to traditional classifications and to recently propounded theories and new approaches to enoplan classification schemes. Several new characters are introduced and their potential significance examined. Finally, a revised classification scheme is presented which leaves open some of the phylogenetic questions about which there is presently much debate but, at the same time, provides secure higher taxa to contain the many forms and groups currently undergoing revision.     

Pollen morphology and systematics of Burseraceae

The Burseraceae are a medium‐sized family in which 18 genera are currently recognised. They are the subject of a long‐term project to describe the pollen morphology from light, scanning electron and transmission electron microscopy. The pollen morphology of tribe Protieae has been published, as well as an account of the pollen of the African taxa in the family. Pollen data for the other two tribes, Bursereae and Canarieae, are more or less complete. The pollen of all the genera have been examined, with the exception of the recently described Pseudodacryodes Pierlot for which, currently, there is no pollen material available. This paper summarises the results.

There is considerable variation in exine and aperture features between, and occasionally within, the genera and 14 major pollen types are defined, including two previously undescribed types: ‘Canarium oleiferum’ and ‘Canarium gracile’. The distribution of pollen characteristics throughout the family is compared with previously published tribal and subtribal groupings, as well as with current ideas of generic relationships from molecular analyses. Comparisons show notable congruence of pollen data with molecular data. To some extent pollen morphology is different for each of the subtribes. Nevertheless, there are some notable exceptions, for example, the pollen of Garuga and Boswellia are remarkably similar, although Garuga has been included, somewhat tenuously, in tribe Protieae, and Boswellia is included in tribe Bursereae, subtribe Boswelliinae. In a recent molecular tree Garuga and Boswellia appear to be closely related, and this supports the conclusion, based on several macromorphological characters as well as pollen, that Garuga should be transferred to tribe Bursereae.     

Pollen and anther development in Nelumbo (Nelumbonaceae)

The Nelumbonaceae are a small family of aquatic angiosperms comprising Nelumbo nucifera and Nelumbo lutea. Historically, the genus has been considered to be closely related to Nymphaeales, however new systematic work has allied Nelumbo with lower eudicots, particularly Platanus. In recent years, studies of pollen development have contributed greatly to the understanding of phylogenetic relationships, but little has been known about these events in Nelumbo. In this paper, pollen and anther development are morphologically described for the first time in N. lutea. A comprehensive ontogenetic sequence is documented, including the sporogenous tissue, microspore mother cell, tetrad, free spore, and mature pollen grain stages. The deposition of a microspore mother cell coat and callose wall, the co-occurrence of both tetrahedral and tetragonal tetrads, the formation of a primexine in tetrads, and primexine persistence into the late free spore stage are shown. The majority of exine development occurs during the free spore stage with the deposition of a tectate-columellate ectexine, a lamellate endexine, and an unusual granular layer below and intermixed with the endexine lamellae. A two-layered intine forms rapidly during the earliest mature pollen stage. Major events of anther development documented include the degradation of a secretory-type tapetum during the free spore stage and the rapid formation of U-shaped endothecial thickenings in the mature pollen grain stage. The majority of mature pollen grains are tricolpate, however less common monosulcate and diaperturate grains also develop. Co-occurring aperture types in Nelumbo have been suggested to be an important transition in angiosperm aperture number. However, aperture variability in Nelumbo may be correlated with the lateness of aperture ontogeny in the genus, which occurs in the early free spore stage. This character, as well as other details of pollen and anther ontogeny in Nelumbo, are compared to those of Nymphaeales and Platanus in an effort to provide additional insight into systematic and phylogenetic relationships. Although Nelumbo is similar to both groups in several characters, the ontogenetic sequence of the genus is different in many ways.     

Platyhelminth systematics and the emergence of new characters

Since the inclusion of molecular data in modern phylogenetic analyses, significant progress in resolving the origins and radiation of flatworms has been made, although some key problems remain. Here I review developments in the supply and use of systematic characters that provide the basis for diagnosis and phylogeny reconstruction, that in turn have driven systematic revisions and the interpretation of broader evolutionary patterns and processes; focus is placed on the parasitic taxa. Although useful tools have been refined to the point of becoming established systematic markers of broad utility, attention to the need for denser gene and taxon sampling is addressed in the light of unresolved questions and current trends in molecular systematics, from nucleotide to genome. Tradition and the nature of available comparative information tends to dictate the choice of systematic markers, but faced with incongruent phylogenies, the emergence of new technologies and the need for rapid species diagnosis, there is a pressing need to assess and standardize our choice of tools so they are fit for purpose, available to all and used widely. I present a brief review of existing and potential sources of phylogenetic characters and discuss their likely value in the context of the systematics and diagnostics of parasitic flatworms.     

Pollen embryogenesis in anther cultures of Solanum carolinense L.

The direct differentiation of bicellular pollen grains of Solanum carolinense L. (Horse-nettle; Solanaceae) into embryoids and plantlets was induced by culturing whole anthers on Murashige and Skoog's medium supplemented with IAA. The highest frequency of embryogenic induction occurred at 10 mg/l IAA. Developmentally, both the generative and vegetative cells of the pollen grain contributed to embryoid formation whose pattern of development was similar to that of zygotic embryos. In a previous study, it was show that 2,4-D promoted callus formation by pollen grains in cultured anthers of S. carolinense. It appears then that there are two distinct pathways of androgenesis in this species that are determined by the type of auxin present in the medium.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - BA benzyladenine - KIN kinetin - MS Murashige and Skoog     

Pollen morphology and systematics of Atripliceae (Chenopodiaceae)

Pollen morphology of 58 species from 17 putative genera of the tribe Atripliceae (Chenopodiaceae) was investigated using light (LM) and scanning electron microscopy (SEM). Morphological variation was analyzed based on a dense sampling of the subtribes Atriplicinae and Eurotiinae, including many of the species in the two largest genera: Atriplex and Obione. The pantoporate pollen grains of Atripliceae are characterized by their spheroidal or subspheroidal shape, flat or moderately vaulted mesoporia with 21–120 pores, tectum with 1–8 spinules and 5–28(?38) puncta per?µm², and 1–13 ectexinous bodies bearing 1–7 spinules each. Taxonomic relevance of the most important pollen morphological characters is discussed (pollen diameter, pore number, pore diameter, interporal distance, spinule and puncta density and ratio, number of ectexinous bodies, and their spinules). Pollen morphological data support the exclusion of Suckleya from the tribe and the recognition of subtribe Eurotiinae, but suggest that it needs to be reviewed. Pollen does not support generic recognition of Atriplex, Neopreissia and Obione and infrageneric subdivisions as currently recognized, and suggests the need to review them. Smaller or monotypic genera, such as Axyris, Ceratocarpus, Endolepis, Krascheninnikovia, Microgynoecium, Proatriplex and Spinacia have distinctive pollen morphological characters that support their generic status. Grayia needs to be reevaluated; although its two species are distinct from all the other species in the study, there are notable differences between each of them, and this suggests they may not form a natural group. Multivariate techniques were employed to investigate if there are discrete patterns of variation within Atripliceae. Principal Component Analyses (PCA) weakly differentiates four groups based on variation in pore number, puncta density per?µm², and ratio between spinule and puncta density per?µm²; species of Ceratocarpus, Haloxanthium, Krascheninnikovia, Manochlamys, Microgynoecium, Spinacia, and some species of Atriplex and Obione are isolated. Preliminary results indicate that pollen data are potentially useful in the classification of the tribe, and further studies will be of taxonomic value.     

Pollen and anther ontogeny in Cabomba caroliniana (Cabombaceae, Nymphaeales)

Cabomba is a small water lily genus that is native to the New World. Studies of pollen development and associated changes in the anther yield valuable characters for considering the evolution of reproductive biology in seed plants. Here we characterized the complete ontogenetic sequence for pollen in Cabomba caroliniana. Anthers at the microspore mother cell, tetrad, free microspore, and mature pollen grain stages were studied using scanning electron, transmission electron, and light microscopy. Tetragonal and decussate tetrads both occur in C. caroliniana, indicating successive microsporogenesis. The exine is tectate-columellate, and the infratectal columellae are the first exine elements to form, followed by a continuous tectum and a thin foot layer. A lamellate endexine initiates in the early free microspore stage, but becomes compressed in mature grains. Tectal microchannels and sculptural rods also initiate during the early free microspore stage, and significant pollenkitt deposition follows, supporting the hypothesis that these elements function in entomophily. The tapetum is morphologically amoeboid, with migratory tapetal cells directly contacting developing free microspores within the anther locule. Results from this study illustrate the importance of including ontogenetic data in analyzing pollen characters and in developing evolutionary and ecological hypotheses. The new palynological data also emphasize the character plasticity that occurs in basal angiosperms.     

Pollen wall characters with emphasis upon applicability

The message for exine pattern resides ultimately in the genome, yet the information for the initial form exists in the cytoplasm or with the plasma membrane and its glycocalyx. Subsequent wall development is likely to be the result of an interplay between the genome, the cytoplasm, and the intralocular environment. The exine consists of units derived from the plasma membrane glycocalyx and enveloped in the exinous polymer sporopollenin. Growth of the exine in accomodation to cell surface expansion is modeled as involving a doubling in diameter of the units, separation of components, and incorportation of new units within the nexine but not the tectum. If the tectum is thick and does not become disjunct, its restraint upon cellular expansion may result in the crushing of bacules. Both the final shape and ornamentation of the exine may be influenced by cytological processes like oncoid plugs that limit the effect of protoplast expansion to nonapertural regions or globules in the exine arcade that can cause distention of the tectum and rupturing of bacules. Subunits of exinous units can be seen in distinctive patterns at the outer surface of the exine, in the arcade of the exine, and prior to intine formation at the inner surface of the nexine.     

Pollen plant formation from anther cultures of Digitalis obscura L.

Factors favouring pollen callus proliferation, induction of embryogenesis and plant regeneration from cultured anthers of Digitalis obscura L. were determined. The presence of auxins was essential for cell proliferation and morphogenesis, and incubation in darkness singificantlyincreased these responses. Callus proliferation usually preceded embryo development, although sometimes direct embryogenesis was observed. On the other hand, bud differentiation was achieved only when callus was transferred to media containing cytokinin or several auxin/cytokinin combinations. Different ploidy levels] were observed in the regenerated plants, with approximately 50% being haploid.     

On the information content of characters in comparative morphology and molecular systematics

A review of the fundamental difference between single molecular-sequence positions, or numerical characters, and complex morphological characters is the subject of this study. It has been found that transformation series of single complex structures contain enough information to allow a priori determination of character order and that rooting of a dendrogram is possible without out-group comparison, while trees based on less-informative characters can usually only be rooted with out-group comparison. Furthermore, the quality of total information used is decisive in discriminating between hypotheses of relationships. Numerical methods for the inference of phylogenies have been found to be useful for high numbers of characters that have only a low information content, while the Hennigian procedure seems to be preferable for complex characters.

Zusammenfassung

Ein fundamentaler Unterschied zwischen der einzelnen Sequenzposition oder auch numerischen Merkmalen und komplexen morphologischen Merkmalen ist ihr Informationsgehalt. Merkmalsreihen komplexer Strukturen enthalten meist genügend Information, um a priori die Bestimmung der Lesrichtung zu ermöglichen. Die Feststellung des Ursprunges eines Dendrogramms ist somit ohne kladistischen Außengruppenvergleich möglich, während Bäume (Topologien), die auf wenig informativen Merkmalen beruhen, allgemein nur mit dem kladistischen Außengruppenvergleich 'gewurzelt' werden können. Die Qualität der insgesamt verwendeten Information ist entscheidend für die Wahl zwischen alternativen Verwandtschaftshypothesen. Numerische Methoden der Rekonstruktion der Phylogenese sind nützlich bei Verwendung einer gro β en Zahl informationsarmer Merkmale; das Hennigsche Verfahren ist für komplexe Merkmale vorzuziehen.     

On the information content of characters in comparative morphology and molecular systematics

A review of the fundamental difference between single molecular-sequence positions, or numerical characters, and complex morphological characters is the subject of this study. It has been found that transformation series of single complex structures contain enough information to allow a priori determination of character order and that rooting of a dendrogram is possible without out-group comparison, while trees based on less-informative characters can usually only be rooted with out-group comparison. Furthermore, the quality of total information used is decisive in discriminating between hypotheses of relationships. Numerical methods for the inference of phylogenies have been found to be useful for high numbers of characters that have only a low information content, while the Hennigian procedure seems to be preferable for complex characters.     

植物系统学研究中常用基因分子标记特点分析

阐述了目前用于植物系统学和进化研究的一些常用的ＤＮＡ分子标记技术,分析了各自的使用范围和应用特点,提出在使用这些分子标记来研究分子系统学时必须注意的问题。     

rRNA二级结构序列用于真菌系统学研究的方法初探

本文首次利用核酸二级结构特征代替核酸碱基作为探讨类群之间亲缘关系的信号,构建了基于结构特征的子囊菌部分类群的系统进化树。该方法以S(规范的碱基对),Q(不规范的碱基对),I(单链),B(侧环),M(多分枝环)和H(发卡结构)为代码将二级结构特征区分为6种不同的亚结构类型,然后将二级结构特征转换为结构序列,并进行结构序列分析。该方法使rRNA不只局限于碱基比较,拓展了其应用范围,为揭示分子的功能与进化的关系提供了线索。结果表明,结构序列分析可用于子囊菌的系统学研究;相对于核酸序列分析,结构分析的结果似乎更加清晰地体现子囊果的演化过程。     

Contribution of pollen and tapetal characters to the systematics of Triuridaceae

 Pollen and tapetal characters in the mycoheterotrophic monocot family Triuridaceae are here compared with those of their putative relatives, including the lilioid order Pandanales (Pandanaceae, Cyclanthaceae, Velloziaceae and Stemonaceae), with which Triuridaceae have recently been associated following analyses of molecular data. Triuridaceae have small, inaperturate (functionally monoaperturate) pollen grains with the exine reduced to gemmae which have distinctive protruberances or spines. Microsporogenesis is of the successive type. Some genera have a plasmodial tapetum. Orbicules are absent. These characters are compatible with a relationship with Pandanaceae, but a relationship with Alismatales, as suggested by earlier authors, cannot be excluded. Received June 18, 2002; accepted July 22, 2002 Published online: November 22, 2002 Address of the authors: Carol A. Furness (e-mail: c.furness@rbgkew.org.uk), Paula J. Rudall and Alison Eastman, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK.     

Orchid embryology: Pollen tetrads of Epidendrum scutella in the anther and on the stigma

Summary The pollinium of Epidendrum scutella, both in the anther and on the stigma, was examined with the electron microscope. The sporoderm of the outer tetrads has a sexine and an intine while that of the inner tetrads lacks a sexine, and an intine is formed only after the pollinium is on the stigma. A fibrous wall layer apparently holds the tetrads together. The cytoplasm is filled with plastids, mitochondria, polysomes, vacuoles and vesicles of various sizes, and endoplasmic reticulum (ER) with narrow cisternae. The vegetative nucleus is oval in form and contains a large nucleolus. The generative nucleus is deeply lobed and contains a well-developed nucleolus. The generative cytoplasm lacks both plastids and mitochondria and has little ER. Dictyosomes are present as well as assorted vesicles. A pocket is present between the plasma membrane of the generative cell and the wall; it contains assorted membranes and ribosome-like particles. After the pollen is on the stigma the wall surrounding the generative cell begins to disappear and gaps develop in it.This investigation was carried out during the tenure of a research fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.Research supported by grants from National Science Foundation (GB-3460) and the Miller Institute for Basis Science at the University of California, Berkeley. The authors would like to thank Miss Mary Ashton for her assistance in the research.     

Comparison of phylogenetic signal between male genitalia and non-genital characters in insect systematics

It is generally accepted that male genitalia evolve more rapidly and divergently relative to non-genital traits due to sexual selection, but there is little quantitative comparison of the pattern of evolution between these character sets. Moreover, despite the fact that genitalia are still among the most widely used characters in insect systematics, there is an idea that the rate of evolution is too rapid for genital characters to be useful in forming clades. Based on standard measures of fit used in cladistic analyses, we compare levels of homoplasy and synapomorphy between genital and non-genital characters of published data sets and demonstrate that phylogenetic signal between these two character sets is statistically similar. This pattern is found consistently across different insect orders at different taxonomic hierarchical levels. We argue that the fact that male genitalia are under sexual selection and thus diverge rapidly does not necessarily equate with the lack of phylogenetic signal, because characters that evolve by descent with modification make appropriate characters for a phylogenetic analysis, regardless of the rate of evolution. We conclude that male genitalia are a composite character consisting of different components diverging separately, which make them ideal characters for phylogenetic analyses, providing information for resolving varying levels of hierarchy.
© The Willi Hennig Society 2009.     

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.