Pollen Wall Development in Gibasis (Commelinaceae)

The development of the one and-inline of the pollen wall aredescribed for Gibasis karwinsk yana and G. venustula. Duringthe tetrad stage the appearance of electron-opaque depositionsor tri-partite plates at discrete sites between the plasma membraneof the spore and the inward surface of the callose special wallare the first indications of exine development. The sulcus rapidlydifferentiates being composed of discrete exine granules ona thin foot layer. Probacula in non-apertural areas developin an electron-opaque granular layer situated between the plasmamembrane, which is highly convoluted, and the callose specialwall. A foot layer is formed from electron-opaque lamellae atthe plasma membrane. Exine pattern is clearly established withinthe tetrad. After release of the spores from the tetrad an intimate associationis rapidly developed between the plasma membrane of the periplasmodialtapetum and the newly-formed exine. Compacted electron-opaquematerial is found at the interface between membrane and theexine and vesicular material is added from the tapetum. Theincrease in volume that occurs in both spore and anther is accompaniedby considerable vacuolation. Intine development begins just prior to pollen grain mitosisand continues rapidly at the aperture. The thin foot layer becomesdiscontinuous. Further intine deposition takes place after mitosisand a bilayer is apparent in mature grains. The matrix of thislayer contains conspicuous electron-opaque platelets. The exineof the mature spore stains less intensely than in the youngspore and the interbacula spaces are filled with material fromthe degenerate tapetum. Gibasis karwinskyana, Gibasis venustula, Commelinaceae, exine, intine, tapetum, pollen wall, ultrastructure     

The Apertural Wall in Pollen of Linum grandiflorum

The apertural wall in tricolpate pollen of Linum grandiflorumwas investigated in order to understand its functioning duringdesiccation and rchydration. Whole and sectioned pollen grainswere studied with light or electron microscopy and by cytochemicalmeans. The areas of the apertures were examined in fresh drypollen, in grains moistened on agar gel or removed from compatiblestigmas, and in pollen from mature undehisced anthers The intine was found to consist of an inner ß-glucanlayer and an outer pectic layer. At the apertures the pecticlayer is thickened and overlaid by a ß-glucan layer.The pectinaceous intine stains red with basic fuchsin. The presenceof a third wall layer, the medine, was not confirmed. The aperturalintine thickenings possess considerable imbibitional capacityand at rehydration they appear as swollen lenticular bodies A procedure is described for obtaining intact exine free grains(EFG's) and whole, separated exines of L. grandiflorum. Invariably,the released EFG's consisted of protoplasts encased in the cellulosicintine. In most grains the outer intine remained attached tothe separated exine In L. grandiflorum the outer wall of the aperture expands whilethe protoplast and endintine are still infolded. Apparently,the exintine becomes detached from the endintine during desiccationand re-attaches at rehydration. It is suggested that the transientdetachment controls the influx of water into the vegetativecell Except for morph-specific exine processes no differences instructure of the aperture wall or its functioning at rehydrationwere observed between pin and thrum grains Pollen wallM, apertures, exintine, exine free grains, rehydration, desiccation, Linum grandiflorum     

Specificity of the Callose Response in Stigmas of Brassica

The specificity of pollen in the induction of callose in stigmasof Brassica spp. has been examined. Callose is induced by fractionsfrom self pollen and pollen of another crucifer, Sinapis arvensis,but not from compatible pollen. Response is blocked by pre-treatment of stigmas with concanavalinA and Triton X-100. Brassica spp., callose, incompatibility, pollen-stigma interactions, recognition     

Pollen coatings – chimaeric genetics and new functions

Pollen coatings have long been assumed to play a pivotal role in pollen-stigma interactions, but until now little clear evidence supporting such a function has been available. Recently, however, the use of isolated coatings of Brassica sp. in experiments in vivo has unequivocally demonstrated that the pollen coat layer is responsible for activation of the stigmatic surface, and that it contains the male determinant of the self-incompatibility system. Surprisingly, molecular analysis of the Brassica pollen coat reveals this layer to include both sporophytic and gametophytic components, the latter including a family of small highly-charged proteins which interact with stigmatic molecules known to be encoded by the S(incompatibility)-locus. Most recently, work on Brassica and Arabidopsis suggests that the adhesive function of the coating is more complex than suspected and involves both stigmatic factors and the exine surface itself. Despite this new insight into the genetics and function of pollen coatings, the mechanisms by which components of these layers are formed in the tapetum and translocated to the pollen grain surface remain far from clear. Received: 29 November 1999 / Revision accepted: 18 January 2000     

The Microfibrillar Component of the Pollen Intine Some Structural Features

The microfibrillar polysaccharide component of the pollen intinecan be isolated by progressive chemical digestion of the exineand the cellular contents and the extraction of the matrix materials.The resulting intine ‘ghosts’ reveal various characteristicstructural features. The microfibrils have apparent individualdiameters in the range of 5–15 nm, but they are commonlyassociated laterally to form ribbons, or aggregated in strandsor cables of dimensions great enough to be resolved with theoptical microscope. These often show preferred orientations,which can be associated with pollen grain shape and with thedisposition-of the germination apertures. The apertural intinemay be structurally complex, as in Abutilon hybridum, where,after the removal of the exine, the polysaccharide caps whichoverlie the protein storage sites of the pollen grain wall retainthe elaborate patterning of the original cytoplasmic evaginationsfrom the vegetative cell. Secale cereale, Narcissus pseudonarcissus, Abutilon hybridum, Crocus vernus, pollen grain, intine, exine, wall pattern, germination apertures, polysaccharide microfibrils, fluorescence microscopy     

Pollen-wall Proteins: 'Gametophytic' and 'Sporophytic' Fractions in the Pollen Walls of the Malvaceae

Proteins are stored in two sites in the pollen grain walls ofthe Malvaceae, (a) in the cellulosic intine, mainly in the vicinityof the circular apertures, and (b) in cavities in the sculpturedlayer of the exine. The intine-held materials are incorporatedduring the growth of the wall. The exine materials are derivedfrom the tapetum, which during dissolution releases cistemaewith a granular-fibrillar content bounded by ribosomal membranes.This fraction is injected into the exine cavities after thecompletion of wall growth through micropores in the tectum.PAS-reacting material is associated with the injected protein.Another tapetal fraction, lipid in nature and commonly containingcarotenoids, remains on the surface of the pollen grains toform the Pollenkitt. While protein can be detected cytochemically in both intineand exine sites, acid phosphatase and ribonuclease activitywas found to be associated only with the former. Immunofluorescencemethods using antiserum to total pollen leachates showed thatantigens are present in both sites. When the pollen grains are moistened, the exine-held proteinsbegin to pass out through the micro-pores in the tectum within30 s of moistening, while the main discharge from the aperturalintine follows in 4–5 min. These observations, together with evidence from other families,suggest that the intine-held proteins of angiosperm pollen grainsare always produced by the male gametophyte, while those heldin exine cavities are sporophytic in origin, being derived fromthe tapetum. As previously proposed, it seems probable thatin intraspecific incompatibility systems of the gametophytictype control is mediated through intine-held ‘recognitionsubstances’, whereas in sporophytic systems the exine-heldmaterials are concerned.     

Polyethylene glycol improves the in vitro growth of Brassica pollen tubes without loss in germination

The culture media for the in vitro pollen assay of Brassicaspecies have so far shown good percentage germination, but limitedpollen tube growth. It is reported here that by lowering sucroseconcentration from 20% to 5 or 10 % and by adding polyethyleneglycol 4000 in the culture medium, high percentage germinationand high tube growth (10 times that in the standard media) canbe achieved in three species of cultivated Brassica. This improvedmedium should be useful in fundamental and applied studies onthe pollen biology of Brassica species. Key words: Brassica, pollen, pollen germination, pollen tube growth, polyethylene glycol     

Pollen morphology,ultrastructure and taphonomy of the Neuradaceae with special reference to Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond.

Pollen morphology and sporoderm ultrastructure of modern Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond. were studied using light (LM) and electron (SEM and TEM) microscopy. Additionally late Holocene pollen of the Grielum-type was studied using LM. Systematic and ecological aspects have been discussed for the family Neuradaceae. The pollen grains of the studied species are characterized by similarities in size, shape, aperture type and differences in exine sculpture (reticulate semitectate exine in Neurada and finely reticulate to foveolate in Grielum) and sporoderm ultrastructure. The cavea in the exine is situated between the ectexine and endexine which are connected near the aperture region only. A combination of the palynological characters of the Neuradaceae (semitectate exine, rather loose columellae, interrupted foot layer, the cavea in the exine) increases the pollen plasticity, allowing considerable changes of the pollen grain volume but still remains insufficient to survive sharp fluctuations in hydration level.     

Pollen Tetrads of Hedycarya arborea J. R. et G. Forst. (Monimiaceae)

Hedycarya has pollen in permanent tetrads. H. arborea, the New Zealand species, differs from others studied, in having a cap of more or less imperforate tectum at the distal pole of each grain. This polar region is not an aperture and the pollen tube emerges through a papillose part of the external wall of each grain. Transmission electron microscope studies of immature and mature tetrads reveal a most unusual exine structure. "Radial processes" develop by accumulation of sporopollenin around unit membranes of similar dimensions to the plasmalemma, and extend from just beyond the intine to the tectal region. The entire exine is considered ectexinous. During development, members of a tetrad are interconnected by cytoplasmic channels and the synchronous division into generative and vegetative nuclei within each tetrad is attributed to their presence. The channels become closed by the deposition of intine. Comparisons are made with exine structure in some other members of the woody Ranales and with some other plants with tetrad pollen.     

The Transfer of Pollenkitt in Smyrnium perfoliatum (Apiaceae)

In Smyrnium perfoliatum the formation of pollenkitt within asecretory tapetum, and the subsequent breakdown of the cellorganelles, is followed by the transformation of pollenkittlumps into pollenkitt droplets. These droplets move within alocular fluid towards the pollen exine, where they enter theexine cavities after passing a fibrillar layer (remnants ofthe primexine-matrix) in between the tectum elements. This isfollowed by the fusion of pollenkitt droplets, forming a distinctlayer at the bottom of the exine cavities. Smyrnium perfoliatum L., Apiaceae, tapetum, pollenkitt formation, organelle disintegration, transformation, pollenkitt deposition, primexine matrix     

Changes in the Pollen Grain Wall of Linum grandiflorum following Compatible and Incompatible Intraspecific Pollinations

The exine surrounding the colpal furrows in the pollen grainsof Linum grandiflorum is rapidly degraded following the twocompatible pollinations between ‘pin’ and ‘thrum’types of flower and also following the incompatible pollinationbetween ‘thrum’ and ‘thrum’. In allthese pollinations the pollen germinates normally. Exine isnot degraded in the incompatible pollination between ‘pin’and ‘pin’. In this pollination the pollen does notswell or germinate. The exine degradation is restricted to thecolpal regions. Hydration of the pollen grain by buffer solutionwithout contact with the stigma also stimulates the degradationof the exine. The erosion of the exine reveals a fibrous, PAS-positivematrix which follows the original contours of the exine. Vesicles are discharged into the intinc following pollination;these appear to contribute their contents to the intine-likewall which eventually invests the pollen tube. The observations are interpreted by assuming:

1. 1. an enzyme situatedwithin the pollen and localized underthe colpi; this enzymeis active after hydration;
2. 2. the degradation is a means bywhich colpal furrows are enlargedto permit the emergence ofthe pollen tube;
3. 3. the degradation process both by bufferand on the stigmais purely the consequence of hydration andis only secondarilyrelated to incompatibility through the ‘pin’by‘pin’ pollination not permitting hydration ofthepollen.

     

Ultrastructure of microsporogenesis and microgametogenesis in Campsis radicans (L.) Seem. (Bignoniaceae)

In the present study, microsporogenesis, microgametogenesis and pollen wall ontogeny in Campsis radicans (L.) Seem. were studied from sporogenous cell stage to mature pollen using transmission electron microscopy. To observe the ultrastructural changes that occur in sporogenous cells, microspores and pollen through progressive developmental stages, anthers at different stages of development were fixed and embedded in Araldite. Microspore and pollen development in C. radicans follows the basic scheme in angiosperms. Microsporocytes secrete callose wall before meiotic division. Meiocytes undergo meiosis and simultaneous cytokinesis which result in the formation of tetrads mostly with a tetrahedral arrangement. After the development of free and vacuolated microspores, respectively, first mitotic division occurs and two-celled pollen grain is produced. Pollen grains are shed from the anther at two-celled stage. Pollen wall formation in C. radicans starts at tetrad stage by the formation of exine template called primexine. By the accumulation of electron dense material, produced by microspore, in the special places of the primexine, first of all protectum then columellae of exine elements are formed on the reticulate-patterned plasma membrane. After free microspore stage, exine development is completed by the addition of sporopollenin from tapetum. Formation of intine layer of pollen wall starts at the late vacuolated stage of pollen development and continue through the bicellular pollen stage.     

Scanning Electron Microscopy Analysis of Exine Patterns in Cultivars of Olive (Olea europaea L.)

Scanning electron microscope analysis of exine patterns in thepollen of nine cultivars of the olive tree (Olea europaea L.)has revealed specific differences between them. The differencesinclude variation in size, form and profile of the meshes andin the thickness of the muri. Every cultivar possesses its ownmorphological characteristics which are constant and are foundin successive years. Olea europaea L, olive, pollen, exine patterns     

Transition within the exine of Nothofagus Blume

Pollen grains with bulged areas on their proximal and distal faces were observed in some species of Nothofagus Blume in the light and electron microscopes. Pollen grains sectioned meridionally are distinctly transitionary in character in the individual strata within the exine of one pollen grain. The tectum in the apocolpia is considerably thinner than in the mesocolpia, The thickness and the character of the bacular layer in the mesocolpia differ greatly from those of the apocolpia. The foot layer, thick and always present in the mesocolpia, is entirely lacking in the apocolpia. The significant difference in the structure and thickness of the bacular layer, as well as the partial absence of the foot layer in one pollen grain, influence the cohesion between the individual strata of the exine in the apocolpia. The cohesion between the tectum and underlying, globular stratum in the central part of the apocolpia is poor, which facilitates the separation of the tectum and its bulging at that area.     

THE AURICULATE POLLEN GRAIN OF HYMENOCALLIS QUITOENSIS HERB. (AMARYLLIDACEAE) AND ITS SYSTEMATIC IMPLICATIONS

The pollen grain of Hymenocallis quitoensis Herb, is examined with scanning and transmission electron microscopy. The very large, monosulcate grain is characterized by a coarsely reticulate exine surface and solid, auriculate appendages at the equatorial facies. Surface morphology of the pollen grain of H. quitoensis is compared with other representative species of Hymenocallis and supports the inclusion of H. quitoensis within the genus. Meridional exine dimorphism in other species of Hymenocallis is interpreted as a reduction from the well-defined auriculae of H. quitoensis. Surface morphology of the pollen grain of Hymenocallis sects. Artema Traub and Elisena (Herb.) Traub exhibits divergence from that of sects. Hymenocallis and Ismene (Herb.) Traub. Phylogenetic and paleobotanical implications of the auriculate pollen grain are briefly discussed.     

水鳖科9属15种植物花粉形态的研究

应用光学显微镜、扫描电镜和透射电镜对水鳖科Hydrocharitaceae 9属15种植物的花粉形态进行 了观察。水鳖科植物花粉为圆球形至近椭球形,无萌发孔或偶为单沟萌发孔,外壁纹饰通常为小刺状纹 饰,刺密集或稀疏,花粉表面具瘤状、疣状、颗粒状、皱波状突起或光滑。外壁由覆盖层、柱状层和基层组 成。覆盖层厚或较薄,柱状层小柱发育不明显,基层薄。水鳖科植物在花粉大小、纹饰类型、刺的长短、 密度、形态、萌发孔的有无以及花粉壁的结构等方面表现出了较为明显的差异,这些特征对探讨类群间 关系具有较重要意义。由于黑藻属Hydrilla和Stratiotes属花粉较为特殊,支持将它们各自作为一个独立 的族处理。水鳖科植物花粉外壁纹饰和结构特点表明该科与水雍科Aponogetonaceae、泽泻科Alismataceae 和花蔺科Butomaceae等近缘,而该科植物花粉大多无萌发孔等则反应了该科与茨藻目Najadales植物有密切联系。     

Insights into a hydration regulating system in Cupressus pollen grains

Background and Aims

Hydration, rupture and exine opening due to the sudden and large expansion of intine are typical of taxoid-type pollen grains. A hemispheric outgrowth external to the exine was observed on Cupressus and Juniperus pollen grains before the intine swelling and exine release. However, the actual existence of this permanent or temporary structure and its precise role in pollen hydration is still being debated. The aim of this paper is to collect information on the actual presence of this peculiar outgrowth on the surface of the Cupressus pollen grain, its structure, composition and function.

Methods

Pollen grains of several Cupressus species were observed using various techniques and methodologies, under light and fluorescence microscopy, phase-contrast microscopy, confocal microscopy, scanning electron microscopy, and an environmental scanning electron microscope. Observations were also performed on other species with taxoid-type pollen grains.

Key Results

A temporary structure located just above the pore was observed on Cupressus pollen grains, as well as on other taxoid-type pollens. It is hemispheric, layered, and consists of polysaccharides and proteins. The latter are confined to its inner part. Its presence seems to regulate the entrance of water into the grains at the beginning of pollen hydration.

Conclusions

The presence of a temporary structure over the pore of taxoid-type pollen grains was confirmed and its structure was resolved using several stains and observation techniques. This structure plays a role in the first phases of pollen hydration.     

The Identification of an Anther Specific Antigen inBrassicaSpecies using a Heterologous Monoclonal Antibody

Monoclonal antibody, MAb 69-139-19, raised against sheep sperm,cross-reacted with anther proteins from fourBrassicaspeciestested. Early in anther development the MAb weakly detecteda polypeptide of42 kDa. At the mid-maturation stage the MAbstill bound weakly to this band but it also detected a polydisperseband of Mr 160–230 kDa. In mature pollen MAb 69-139-19labelled the polydisperse region of 160–230 kDa very strongly,as well as a faint, but distinct, band of116 kDa. Immunogoldlabelling ofB. napusL. anthers and pollen grains also showeda differential pattern of labelling. At the early vacuolatestage the MAb recognized an antigen within the tapetum and themicrospore cytoplasm and nucleus. During the late vacuolatestage the MAb bound to the tapetal material during transferto the pollen grain wall, leading to strong labelling of thepollen wall at maturity. In sheep MAb 69-139-19 binds to thepostacrosomal region of the sperm (Hou, 1989). The polypeptidepresent in plants, which contains the epitope recognized bythe MAb is likely to be a different protein to that in sheep,but we suggest that it plays a role in sexual reproduction inBrassica.It is possible that as the polypeptide is located in the pollencoat it may be involved in pollen/stigma interactions duringpollination leading to successful adhesion and pollen tube germination. Brassica napusL; incongruity; pollen-stigma recognition; pollination; rapeseed; heterologous antibody     

Aberrant pollen in southern African Oxalis (Oxalidaceae)

The formation of aberrant pollen is a well‐known phenomenon reported in various angiosperm families.The presence and range of aberrant pollen grains among southern African members of Oxalis L. were studied by SEM analysis. Seven categories of grain aberrations and two successiform series were identified. Grain aberrations were most frequently found amongst pollen with supra‐areolate exine structures and always affected the number and arrangement of the colpi. The exine structure is never altered. No distinct correlation could be detected between grain aberrations and ploidy levels.     

Società Botanica Italiana Congresso Sociale 1982 Parto—12-14 Ottobre Relazioni

Abstract

« Harmomegathy »: a still open problem not yet well-known. - Wodehouse used the term « Harmomegathy » to indicate the form and volume change in pollen grains, due to water loss or assumption. Roundish and tricolporate grains in the anther become oval and decrease in volume during the dehydration preceeding anthesis. Viceversa during rehydration on the stigma they undergo the opposite process.

Pollen water content at an thesis varies from species to species and it usually ranges between 10 and 20%; nevertheless in some families as Zingiberaceae and Araceae it is higher. Anther and pollen dehydrations are affected by environmental factors, such as humidity of air and temperature, before the anthesis and when pollen is suspended in air. Besides, to avoid the further loss of water during pollen flow, an oily layer derived from tapetum degeneration is deposited outside the pollen grains.

During dehydration and rehydration pollen grains undergo a stress due to shape and volume changes expecially in the colpus and/or pore areas. Pollen walls are structured in order to avoid their own damage, which could be followed by protoplast death and/or irregularities in grain shape. Intine, formed by pectocellulosic filaments, has elastic properties, as sporopollenin, the component of exine.

Stigma can be dry or wet, namely covered or not by stigmatic exudate giving place to different hydration patterns. The structure of intine and exine has to match that of the stigma, in fact pollen will find the best place and way to proper hydration only on stigmas of its own species. Grains structure also must be sterically conform to stigma: this is well-shown in species as Linum, Lytrum and Primula which have an heteromorphic autoincompatibility.

The right keeping of shape and structure of grains, despite the hydration and dehydration, is therefore essential to the physical-morphological recognition between pollen and stigma, which preceedes the biochemical recognition.