Exine Pattern Research Articles

Ultrastructural Characterization of Exine Development of the transient defective exine 1 Mutant Suggests the Existence of a Factor Involved in Constructing Reticulate Exine Architecture from Sporopollenin Aggregates

A male-sterile mutant of Arabidopsis thaliana, in which filament elongation was defective although pollen fertility was normal, was isolated by means of T-DNA tagging. Transmission electron microscopy (TEM) analysis revealed that primexine synthesis and probacula formation, which are thought to be the initial steps of exine formation, were defective, and that globular sporopollenin aggregation was randomly deposited onto the microspore at the early uninucleate microspore stage. Sporopollenin aggregation, which failed to anchor to the microspore plasma membrane, was deposited on the locule wall and in the locule at the uninucleate microspore stage. However, visually normal exine with a basic reticulate structure was observed at the middle uninucleate microspore stage, indicating that the exine formation was restored in the mutant. Thus, the mutant was designated transient defective exine 1 (tde1). These results indicated that tde1 mutation affects the initial process of the exine formation, but does not impair any critical processes. Our results also suggest the existence of a certain factor responsible for exine patterning in A. thaliana. The TDE1 gene was found to be identical to the DE-ETIOLATED 2 gene known to be involved in brassinosteroid (BR) biosynthesis, and the tde1 probacula-defective phenotypes were recovered in the presence of BR application. These results suggest that BRs control the rate or efficiency of initial process of exine pattern formation.

A contribution to the ultrastructural knowledge of the pollen exine in subtribe Inulinae (Inuleae, Asteraceae)

To better understand the relationships within the Asteroideae and Inuleae, the structure of the pollen exine was investigated in seven genera and nine species of the subtribe Inulinae using LM, TEM and SEM. All taxa have a senecioid pattern of exine. The tectal complex consists of three main layers that differ in thickness and morphology: a tectum, a columellar layer, and a layer consisting of the basal region of the columellae. The absence or the vestigial condition of the foramina is considered as a plesiomorphy within the Asteroideae. All taxa have a complex apertural system that consists of an ecto-, a meso-, and an endoaperture. These apertures intersect respectively the tectal complex, the foot layer and the upper part of the endexine, and the inner layer of the endexine. A continuous transition among the different species of Inulinae was found for all the quantitative characters examined. This relative homogeneity of the pollen morphological characters enhances the naturality of the subtribe Inulinae.

Pollen studies in the genus Echinops L. and Xeranthemum group (Asteraceae)

The phylogeny of the genus Echinops and the Xeranthemum complex were the subject of a previous molecular study of the tribe Cardueae. An electronic microscope survey of pollen morphology and ultrastructure is presented for all the genera belonging to these groups, allowing four pollen types to be identified. The exine pattern indicates that there are two pollen types in the genus Echinops (including Acantholepis), although no differences have been found between sections in Echinops. First, the annual species of Echinops and Acantholepis orientalis show a pollen type that differs from that of perennial species of the former genus and, second, the genera Chardinia and Xeranthemum exhibit a pollen type distinct from that Amphoricarpos and Siebera. The internal structure of the pollen wall is the same for all the genera. Only slight differences were observed in the tectum, but in all cases these were of the anthemoid type. Statistically significant correlations between pollen size and the life cycle were found.

Pollen Morphology of the Woody Fabaceae in Korea

The pollen morphology of 31 taxa, representing all woody species from 12 genera of Fabaceae in Korea, was examined by light microscope and scanning electron microscope. The pollen grains were monad and prolate spheroidal or rarely subprolate in equatorial view. The pollen grain aperture was trizonocolporate or rarely trizonooperculate, which does not occur in the other families of Fabales in Korea. The exine showed a great variety of sculpture pattern, i.e. psilate, microperforate, densely microperforate, perforate, polygonal perforate, macroperforate, macroperforate with granules in holes, polygonal macroperforate, verrucate with pitted perforate striae, verrucate-perforate, granulate, rugulate, reticulate or refined reticulate. The pollen morphological data supported the idea that the genera Echinosophora and Sophora were congeneric. Caragana (Galegeae) was quite close to the Sophora group (Maackia, Sophora and Echinosophora) of the Sophoreae in each measured pollen parameter and exine sculpture pattern. Eleven genera of Fabaceae were recognized based on differences in aperture type, pollen grain shape and exine pattern, and a generic pollen key of the woody Fabaceae in Korea was developed. A key to pollen types of Lespedeza was also suggested. The examined taxa of Coronilla and Wisteria were recognized by their exine patterns.

Pollen polymorphism inThymus capitatus(Lamiaceae)

Polymorphism with respect to size and structural characteristics occurs in pollen grains of several species. Pollen grains of Thymus capitatus (L.) Hoffmans & Link. from three different areas of Greece were collected, and their palynological characteristics were measured. Using light and scanning electron microscopy, a quantification of pollen polymorphism of T. capitatus was achieved by measuring the size and the characteristics of exine sculpture. The measurements were repeated during 3 successive years, and statistical analyses with one-way ANOVA and Duncan’s multiple range test were applied. Results revealed differences in the exine pattern between the locations; also, three palynological characteristics (surface, perimeter, and equatorial diameter) differed statistically. The results clearly indicate that pollen grains of T. capitatus are polymorphic between the sampling areas. The polymorphism has been related to environmental parameters and mainly with water availability. Average rainfall seems to be the main factor contributing to the morphological variation of pollen grains by affecting their size and exine sculpture.

Palinotaxonomia de espécies de Lepidaploa (Cass.) Cass. (Vernoniinae - Compositae) ocorrentes no Sudeste do Brasil

Foi realizado o estudo polinico de 23 especies de Lepidaploa (Cass.) Cass. (Vernoniinae-Compositae) ocorrentes no Sudeste do Brasil, com o objetivo de contribuir para a caracterizacao polinica dessas especies, bem como avaliar sua posicao taxonomica. Os graos de polen foram acetolisados, medidos, descritos e ilustrados sob microscopia de luz. Para observar detalhes da superficie e da abertura, graos de polen nao acetolizados foram analisados em microscopio eletronico de varredura (MEV) e, em seguida, eletromicrografados. Foram estudadas as caracteristicas dos graos de polen como forma, tamanho, constituicao da exina e abertura. As especies analisadas nesse estudo possuem graos de polen de tamanho medios ou grandes, isopolares, suboblatos, oblato-esferoidais ou prolato-esferoidais, âmbito subtriangular, area polar pequena ou grande, 3-colporados de superficie equinolofada. Foi confeccionada uma chave para identificacao das especies estudadas com base em dados polinicos. Pode-se concluir que os graos de polen do genero Lepidaploa apresentam quatro padroes principais de organizacao das malhas da exina equinolofada e tres desses padroes podem ser divididos em subtipos de acordo com a forma da lacuna apertural.

Pollenmorphology of the Egyptian species of genusLimoniumMill. (Plumbaginaceae)

AbstractStigma and pollen types are reviewed in eight species of genusLimoniumby light and scanning microscopy. A careful examination of most Egyptian species ofLimoniumreveals that this genus is distinctly dimorphic in stigma and pollen types. On the basis of the stigma type and the exine pattern, two distinct pollen types are recognized viz., Pollen type‐A (comprisesLimonium axillareandL. meyeri) and Pollen type‐B (comprises the rest studied species ofLimonium). Description of each type, a key to the investigated taxa as well as LM and SEM micrographs of pollen grains are provided. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Conventional and novel modes of exine patterning in members of the Araceae – the consequence of ecological paradigm shifts?

In the family Araceae, the members of all subfamilies except Aroideae follow the conventional mode of exine formation pattern, which conforms with the textbook view of sporoderm stratification and chemistry (sporopollenin ektexine formed before the endexine). Only members of the subfamily Aroideae show a quite uncommon mode of exine formation pattern, with an endexine formed prior to the nonsporopollenin, polysaccharidic outer exine layer. The intine is formed simultaneously with this non-sporopollenin layer. From the differing timetable and especially from the different origin it is concluded that this outer exine layer is not homologous to the angiosperm ektexine. The fundamental question, why members of the Aroideae lack an elaborated sporopollenin ektexine, is discussed in terms of functionality of the nonsporopollenin outer exine layer. It seems that a major change in aroid evolution took place at the point when the family phylogenetically and ecologically shifted from bisexual (most subfamilies) to unisexual flowers (Aroideae only). The hypothesis is that ephemeral spathes and the absence of sporopollenin are the consequence of an adaptive syndrome for a short pollination time window in many members of the Aroideae, with short-lived pollen, an energetically not costly pollen wall, rapid germination of pollen tube, and brief receptivity of stigma.

Contributions to the pollen morphology of the tribe Inuleae (subfamily Asteroideae‐Compositae) in the flora of Egypt

AbstractThe pollen morphology of 18 species of tribe Inuleae belonging to 10 genera was examined by light and scanning microscopy. Pollen grains usually trizonocolpate to trizonocolporate rarely 4‐zonocolporate. Shape commonly oblate‐spheroidal to spheroidal, with some suboblate types. Tectum echinate to echinulate. Tectum in‐between the spines or spinules is sub‐psilate, perforate to scabrate or microreticulate. On the basis of the pollen class and the exine pattern, three distinct pollen types are recognized viz., Pollen type‐I: Anvillea garcinii, Pollen type‐II: Nauplius graveolens and Pollen type‐III: Pulicaria . Within the pollen types, pollen characters are significantly sufficient for characterization of the species. An interesting correlation observed is that the taxa having slightly thick exine (4–7 µm) with echinate or echinulate tectum. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pollen exine ornamentation in the F2 generation of an interspecific hybrid of Chorisia (Bombacoideae, Malvaceae) in relation to inheritance pattern

Pollen morphology in ten plants of F2 progeny of an interspecific tree hybrid, Chorisia insignis H. B.& K.×C. speciosa St. Hil (Bombacoideae, Malvaceae) has been studied with a view to have an insight in to the effect of hybridization on the pollen morphological features in F2 generation. The study is a sequel to an earlier study on the pollen morphology of Chorisia species and their F1 hybrid, in which case the hybrid pollen uniformly exhibited the apertural features of the male parent and exine features of the female parent. In the F2 progeny the pollen grains display the apertural feature of the male parent in all the plants. However, with regard to exine ornamentation, variability has been observed. Of the ten plants, two plants exhibit the exine features of the male parent showing empty lumina (without bacula), five plants have their pollen exactly like that of the F1 plant (showing prominent columellar heads in the lumina of the apocolpium region) and the remaining three plants showing columellae in lumina of both apocolpium and mesocolpium region being different from the above types. It has been inferred that the variability in the exine pattern in F2 pollen indicates that the pollen exine pattern in hybrids, perhaps, is not unequivocally controlled by sporophytic or gametophytic genomes.

Apricot (Prunus armeniaca) pollen morphological characterisation through scanning electron microscopy, using multivariate analysis

Pollen grains of 11 Iranian apricot (Prunus armeniaca) cultivars were examined, using scanning electron microscopy (SEM). Pollen was collected in the 2002 growing season from mature apricot trees grown in The Apricot Collection Orchard, Ismailabad Horticultural Research Station, Qazvin, Iran. For SEM evaluation, pollen grains were observed and photographed at 1000× for whole grain and at 10 000× for sectioning of exine pattern (surface topography). The length (L) and the width (W) of grain, L/W ratio, distance between two furrows and the width of ridges in elliptical pollen, and the base, the altitude and the width of grain and ridges in triangular pollen were measured. Substantial variability in the size, shape, and exine patterns among pollen grains was clearly distinguished. The apricot cultivars were easily separated into two groups according to their pollen grain shapes: (1) elliptical trizonocolpate (five cultivars); and (2) obtuse‐triangular (six cultivars). The pollen grains of all studied apricot cultivars were medium in size: 51.32 × 25.51 μm (length × width) for the elliptical shape, and for the triangular shapes: 39.03 × 31.22 μm (base × altitude). The resultant data from the two types of pollen shapes were analysed using completely randomised design (CRD) with unequal replications. Moreover, multivariate statistical analysis was carried out to distinguish morphometric information from measured parameters of the two pollen grain shapes. The projections of the loadings defined by the first two principal components allowed for the visualisation of the position of apricot cultivars, demonstrating between‐cultivar‐pollen shape variations. Hence, the differences in both exine pattern and surface topography, in particular ridges and pore characteristics, can potentially be used as a diagnostic tool to aid in the identification of apricot cultivars.

Callose (β-1,3 glucan) is essential for Arabidopsispollen wall patterning, but not tube growth

BackgroundCallose (β-1,3 glucan) separates developing pollen grains, preventing their underlying walls (exine) from fusing. The pollen tubes that transport sperm to female gametes also contain callose, both in their walls as well as in the plugs that segment growing tubes. Mutations in CalS5, one of several Arabidopsis β-1,3 glucan synthases, were previously shown to disrupt callose formation around developing microspores, causing aberrations in exine patterning, degeneration of developing microspores, and pollen sterility.ResultsHere, we describe three additional cals5 alleles that similarly alter exine patterns, but instead produce fertile pollen. Moreover, one of these alleles (cals5-3) resulted in the formation of pollen tubes that lacked callose walls and plugs. In self-pollinated plants, these tubes led to successful fertilization, but they were at a slight disadvantage when competing with wild type.ConclusionContrary to a previous report, these results demonstrate that a structured exine layer is not required for pollen development, viability or fertility. In addition, despite the presence of callose-enriched walls and callose plugs in pollen tubes, the results presented here indicate that callose is not required for pollen tube functions.

Molecular phylogeny, recent radiation and evolution of gross morphology of the rhubarb genus Rheum (Polygonaceae) inferred from chloroplast DNA trnL-F sequences.

Rheum, a highly diversified genus with about 60 species, is mainly confined to the mountainous and desert regions of the Qinghai-Tibetan plateau and adjacent areas. This genus represents a good example of the extensive diversification of the temperate genera in the Qinghai-Tibetan plateau, in which the forces to drive diversification remain unknown. To date, the infrageneric classification of Rheum has been mainly based on morphological characters. However, it may have been subject to convergent evolution under habitat pressure, and the systematic position of some sections are unclear, especially Sect. Globulosa, which has globular inflorescences, and Sect. Nobilia, which has semi-translucent bracts. Recent palynological research has found substantial contradictions between exine patterns and the current classification of Rheum. Two specific objectives of this research were (1) to evaluate possible relationships of some ambiguous sections with a unique morphology, and (2) to examine possible occurrence of the radiative speciation with low genetic divergence across the total genus and the correlation between the extensive diversification time of Rheum and past geographical events, especially the recent large-scale uplifts of the Qinghai-Tibetan Plateau. The chloroplast DNA trnL-F region of 29 individuals representing 26 species of Rheum, belonging to seven out of eight sections, was sequenced and compared. The phylogenetic relationships were further constructed based on the sequences obtained. Despite the highly diversified morphology, the genetic variation in this DNA fragment is relatively low. The molecular phylogeny is highly inconsistent with gross morphology, pollen exine patterns and traditional classifications, except for identifying all samples of Sect. Palmata, three species of Sect. Spiciformia and a few species of Sect. Rheum as corresponding monophyletic groups. The monotypic Sect. Globulosa showed a tentative position within the clade comprising five species of Sect. Rheum. All of the analyses revealed the paraphyly of R. nobile and R. alexandrae, the only two species of Sect. Nobilia circumscribed by the possession of large bracts. The crude calibration of lineages based on trnL-F sequence differentiation implied an extensive diversification of Rheum within approx. 7 million years. Based on these results, it is suggested that the rich geological and ecological diversity caused by the recent large-scale uplifts of the Qinghai-Tibetan Plateau since the late Tertiary, coupled with the oscillating climate of the Quaternary stage, might have promoted rapid speciation in small and isolated populations, as well as allowing the fixation of unique or rare morphological characters in Rheum. Such a rapid radiation, combined with introgressive hybridization and reticulate evolution, may have caused the transfer of cpDNA haplotypes between morphologically dissimilar species, and might account for the inconsistency between morphological classification and molecular phylogeny reported here.

The HKM gene, which is identical to the MS1 gene of Arabidopsis thaliana, is essential for primexine formation and exine pattern formation

A male-sterile mutant of Arabidopsis thaliana was isolated by T-DNA tagging screening. Using transmission electron microscopy analysis, we revealed that the microspores of this mutant did not have normal thick primexine on the microspore at the tetrad stage. Instead, a moderately electron-dense layer formed around the microspores. Although microspores without normal primexine failed to form a proper reticulate exine pattern at later stages, sporopollenin was deposited and an exine-like hackly structure was observed on the microspores during the microspore stage. Thus, this mutant was named hackly microspore (hkm). It is speculated that the moderately electron-dense layer was primexine, which partially played its role in sporopollenin deposition onto the microspore. Cytological analysis revealed that the tapetum of the hkm mutant was significantly vacuolated, and that vacuolated tapetal cells crushed the microspores, resulting in the absence of pollen grains within the anther at anthesis. Single nucleotide polymorphism analysis demonstrated that the hkm mutation exists within the MS1 gene, which has been reportedly expressed within the tapetum. Our results suggest that the critical process of primexine formation is under sporophytic control .

Pollen morphology of the Chloridoideae (Gramineae)

Pollen grains of 57 species (representing 42 genera) of the Chloridoideae have been investigated using light, scanning and transmission electron microscopy. Two aperture patterns and nine exine patterns are distinguished using SEM and TEM. These are categorized into five pollen types. Two pollen types are previously not recorded in Gramineae. A key for the identification of these pollen types is presented. Generally, pollen characters have limited systematic value in recognizing taxa at generic level or above in the Chloridoideae. An evolutionary trend is proposed that awaits verification by further systematic study. Pollen characters can be used as indicators for the areas of origin and distribution of the Chloridoideae.

Exine development in Encephalartos altensteinii (Cycadaceae): ultrastructure, substructure and the modes of sporopollenin accumulation

It has been found that in Encephalartos altensteinii all the main characters of the exine appear within the tetrad period. The framework of the exine—the plasma membrane glycocalyx—appears first and consists of close packed cylinder-like units 120–160 nm in diameter, oriented perpendicular to the microspore plasma membrane. The main character of the glycocalyx framework is its dynamism: the units are capable of building up throughout the period of exine development. Sporopollenin acceptor particles (SAPs) occur distributed alongside the walls of the cylinder-like units, bringing about a sporopollenin accumulation and the appearance of cylindrical alveolae of the exine pattern. The location of SAPs, which are probably enzyme molecules, is carried out mainly under control of genome, and only the final step occurs by self-orientation, as a result of a combination of both strong and weak interactions between glycocalyx macromolecules and enzyme molecules. The initial accumulation of sporopollenin apparently occurs in the form of microglobules around SAPs with diameter of 30–50 nm. Subsequent sporopollenin accumulation, which results in the appearance of the mature alongate alveolate pattern of the exine, is independent of SAPs and can be regarded as secondarily accumulated sporopollenin. We suggest two stages in the exine development which are realized by self-assembly: (i) the formation of the glycocalyx and (ii) the accumulation of receptor-independent sporopollenin. The intermediate stage—the initial accumulation of receptor-dependent sporopollenin—is carried out under the control of SAPs.

World Pollen and Spore Flora 23. Malvaceae Adams. P.p. Subfamilies: Grewioideae, Tilioideae, Brownlowioideae

The pollen morphology of 85 species (89 collections) from 32 genera, i.e. Ancistrocarpus, Apeiba, Berrya, Brownlowia, Carpodiptera, Christiana, Clappertonia, Colona, Corchorus, Desplatsia, Diplodiscus, Duboscia, Eleutherostylis, Entelea, Erinocarpus, Glyphaea, Goethalsia, Grewia, Hainania, Heliocarpus, Luehea, Lueheopsis, Microcos, Mollia, Mortoniodendron, Pentace, Sparmannia, Tetralix, Tilia, Trichospermum, Triumfetta, and Vasivaea of family Malvaceae was examined by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Three types are recognized on the basis of aperture types, exine pattern and pollen shape classes 1) Berrya-type, 2) Corchorus-type and 3) Mortoniodendron-type. The Berrya-type has two subtypes: Berrya-subtype A and Berrya-subtype B. Corchorus-type has two subtypes: Corchorus-subtype A and Corchorus-subtype B. In the Berrya-type, Corchorus-type and Mortoniodendron-type pollen grains are colporate, in one case (Tilia) colp(or)ate. The pollen morphological trends are discussed with special reference to pollen size, shape and exine sculpturing.

I ntroduction

BioTechniquesVol. 34, No. 3S IntroductionOpen AccessIntroductionMichael F. Ochs & Andrew K. GodwinMichael F. OchsSearch for more papers by this author & Andrew K. GodwinSearch for more papers by this authorPublished Online:24 Sep 2018https://doi.org/10.2144/mar03introAboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinkedInReddit "Introduction." , 34(S3), pp. S1–FiguresReferencesRelatedDetailsCited ByACOS5 is required for primexine formation and exine pattern formation during microsporogenesis in Arabidopsis8 August 2017 | Journal of Plant Biology, Vol. 60, No. 4Sources of Clostridia in Raw Milk on FarmsApplied and Environmental Microbiology, Vol. 74, No. 20 Vol. 34, No. 3S Follow us on social media for the latest updates Metrics Downloaded 83 times History Published online 24 September 2018 Published in print March 2003 Information© 2018 Author(s)PDF download

Exine development in Stangeria eriopus (Stangeriaceae):: ultrastructure and substructure, sporopollenin accumulation, the equivocal character of the aperture, and stereology of microspore organelles

It has been found that in Stangeria eriopus all the main characters of the ectexine appear within the tetrad period, whereas the lamellated endexine appears at the beginning of the free microspore period. The framework of the exine – the plasma membrane glycocalyx – appears first and consists of closely packed cylinder-like units 120–150 nm in diameter, oriented perpendicularly to the microspore plasma membrane. The main character of the glycocalyx framework is its dynamism: the units are capable of building up throughout the period of exine development. Sporopollenin acceptor particles occur distributed alongside the walls of the cylinder-like units, bringing about a corresponding sporopollenin accumulation and the appearance of long-alveolate exine pattern with cylindrical alveolae. The sporal origin of sporopollenin in Stangeria is most probable; the initial accumulation of this polymer apparently occurs in the form of microglobules. Microspores have rather proximal than distal apertures; at the distal pole a pseudosulcus appears in a very unusual way, the whole process looks like an attempt of the formation of the distal aperture. Quantitative data on the dynamics of the volume density, and absolute volume of the cell components of the developing microspores have revealed the degree of organelle participation during the main processes taking place in the cells. They have revealed an important role of the plasma membrane movements, and contribution of the endoplasmic reticulum and Golgi apparatus to the establishment of the sporoderm.

Pollen morphology and biometry of the genus <i>Androcymbium</i> (Colchicaceae) in southern Africa: taxonomic and biogeographic considerations

Pollen characters in 16 southern African type specimens of Androcymbium Willd. that represent the three sections into which the genus is presently divided (Androcymbium, Dregeocymbium and Erythrostictus), were examined to assess the possibility of sectional characterization based on pollen traits and to explore the relationship between pollen traits and geo­graphic species distribution. Differences in pollen grain size, shape, number of apertures and exine pattern, were observed. Principal Component Analysis, using both qualitative and biometric pollen characters, distinguished four groups of species with four different pollen types. Most of the species have a microreticulate exine pattern with either diaperturate or tria- perturate grains. The remaining species have either a rugulate exine pattern with diaperturate grains, or a rugulate-reticu- late exine pattern with thickened (hypertrophied) muri with diaperturate grains. While section Dregeocymbium can be well delimited by the unique thickened muri. and by a significantly larger grain size, no diagnostic pollen traits were found for sections Androcymbium and Erythrostictus. Similarly, although the six northern African species exhibit a microreticulate exine pattern, the high variability observed for this trait in their southern African counterparts, does not follow a geographic pattern.