Localization of the major allergen Bet v I in birch pollen by confocal laser scanning microscopy

Confocal laser scanning microscopy (CLSM) was used to localize the major allergen, Bet v I in birch pollen. Pollen grains of Belula pendula were collected from catkins that had begun to release their pollen, freeze dried, and stored at 4°C. The pollen material was cryosectioned and stained with indirect immunofluorescence using the monoclonal antibody Bv 10. The observed localization of Bet v I was dependent on the treatment of the grains. When they had been prefixed with gaseous formaldehyde followed by acetone Bet v I was found in the cytoplasm. When the prefixation was omitted, a minor portion of Bet v I also appeared in the exine in the aperture regions. The allergen was not observed in the intine or the Zwischenkörper. Our suggestion is that the normal route for excretion of Bet v I is via the apertures on contact between pollen and the stigmatic surface of the pistil.     

The pollen grain wall as a site for passage of lanthanum in tomato,Lycopersicon esculentum (Solanaceae)

We studied the response of the pollen grain wall to the passage of materials from the external environment. Pollen grains of Lycopersicon esculentum, a species not previously investigated in similar studies, were used to determine whether the routes of passage through the pollen wall are a characteristic of a given species. We found lanthanum deposits on the cell wall surface, inside microchannels crossing tectum, and in the infratectum. Lanthanum was also seen as a fine precipitate homogenously scattered within the substance of the exine. In the apertural region of the intine, electron-dense deposits filled the tubulations of the intine oncus, whereas the intine matrix was free of precipitate. In the cytoplasm, precipitate was observed inside small vesicles frequently located near or in contact with the plasmalemma. Our findings were similar to those reported in other species, and were not influenced by the fixative or culture medium used to incorporate the tracer element. We noted a relation between the route of passage and the stage of pollen grain maturation. In less mature grains (midbicellular pollen), electron-dense deposits were more abundant than in more mature grains, probably because apertural regions were blocked as routes of passage.     

An Ultrastructural Study of Pollen Grains Consumed by Larvae of Osmia Bees (Hymenoptera,Megachilidae)

Pollen samples from provisions and faeces found in the nests of four Osmia species were analyzed by SEM and TEM. The pollen grains studied were Cistus, Sonchus type oleraceus. Primus type dulcis, and Quercus type ilex. The apertures of Cistus and Sonchus pollen stored in the provisions were slightly expanded, and the cytoplasm protruded through them. Conversely, Prunus and Quercus pollen grains showed hardly any signs of such apertural protrusions. Further, the cytoplasm of Cistus and Sonchus pollen (which have thin intines) was almost entirely lacking in the pollen grains recovered from faeces, while in the faecal pollen grains of Prunus and Quercus (with thick intines) the cytoplasm was much less modified. These preliminary results indicate that both the protrusion of the cytoplasm in the provisions and the thickness of the intine may play an important role in the digestion of pollen grains by Osmia bee larvae.     

Interaction of lipid bodies with other cell organelles in the maturing pollen of Magnolia × soulangeana (Magnoliaceae)

The pollen grain maturation in Magnolia × soulangeana was studied ultrastructurally and cytochemically using both the light and transmission electron microscope. Emphasis was given on the storage lipid bodies of the vegetative cell (VC) and their interaction with other cell organelles. Stereological analysis of electron micrographs was performed to evaluate the variation in volume density (V_V), surface density, and surface-to-volume ratio (S/V) of various cell organelles during pollen maturation. The size and numerical density of the lipid bodies, and their frequency of association with other cell organelles, were also determined. It was noted that during pollen ontogeny and maturation, the lipid bodies changed their pattern of distribution in the VC cytoplasm, which may be a good marker for the succeeding stages of pollen development. Also, the size, osmiophily, and V_V of the lipid bodies were progressively reduced during pollen maturation whereas the S/V was significantly increased. This seems to indicate that the lipid bodies are mobilized in part during this period of pollen maturation. In particular, the intermediate and mature pollen showed a high percentage of lipid bodies establishing a physical contact with either glyoxysomes, either protein storage vacuoles, or small vesicles presumably originated from dictyosomes. This physical contact was found in both the chemically fixed and rapid freeze-fixed pollen indicating that it is neither artifactual nor casual. On the basis of this intimate association with other cell organelles and the morphometric analysis performed, we suggest that the mobilization of lipid bodies is likely mediated not only by glyoxysomes but also by other catabolic pathways involving the interaction of lipid bodies with either protein storage vacuoles or small Golgi vesicles.     

Changes in the Plantago lanceolata mature pollen ultrastructure and Pla l 1 allergen localisation after grain hydration

Abstract

We have conducted the study of ultrastructural changes of wall and cytoplasm of Plantago lanceolata (English plantain) pollen grains during the first 10 min of hydration and activation processes, prior to germination, and localisation of Pla l 1, the major allergen of these pollen grains with immunocytochemical methods. The samples were fixed using conventional and freezing protocols for transmission electron microscopy. During the activation process, the intine is thickened in the apertural region and cytoplasm undergoes changes in the number of lipid bodies, amyloplasts, vacuoles and ribosomes. Also, we observed an association between lipid bodies, cisternae of rough endoplasmic reticulum, dictyosomes and vacuoles. An increase in the presence of allergenic particles (Pla l 1) in the exine, intine and the cytoplasm in activated pollen grains was detected, whereas this presence is not significant in mature pollen grains. The increase in the production and release of this allergen when pollen grains are activated suggest that Pla l 1 has an important role in pollen–stigma recognition and in the subsequent development of the pollen tube.     

Unique tetrads of <Emphasis Type="Italic">Epilobium luteum</Emphasis> (Onagraceae: Onagreae) pollen from Alaska

Aperture morphology of tetrad pollen of Epilobium luteum (Onagraceae: Epilobieae) from three Alaskan collections is highly variable. The first collection appears to lack apertures altogether and is presumed to consist of immature pollen gains in a genus known to achieve mature size before the apertures become distinctly protruding. A second collection has tetrads with 3- and 4-apertured grains, the apertures in the latter are often irregularly spaced and not in apposition with the apertures of neighboring members. The third collection consists of the more typical 3-apertured members that characterize the majority of Epilobium pollen grains. In all of these collections individual pollen grains (monads) are interspersed among the tetrads. The variations in the number of apertures emphasize the importance of having a comprehensive understanding of the stage of development of the pollen (taxon) examined when describing pollen collections. In the first collection this would mean the recognition that in Onagraceae apertures occur in the later stages of microspore ontogeny. In the latter two collections a thorough background of the literature of the pollen morphology on this largest Onagraceae taxon is useful for the understanding of the significance of a range of aperture numbers on Epilobium pollen grains.     

Pollen morphology and its taxonomic significance of the monotropoideae (Ericaceae)

A palynological survey, including LM, SEM and TEM is presented for eight genera, nine species and 76 samples of the Monotropoideae which is composed of 10 genera and 13 species. On the basis of the aperture number and shape, the following six pollen types are recognized: 1) 3-colp(oroid) ate—Allotropa, 2) 2-colpor(oid)ate—Monotropsis andHemitomes, 3) 4-colpor(oid)ate—Pterospora, Sarcodes andPleuricospora, 4) 2- and 3-colpor(oid)ate—Monotropa hypopitys, 5) 3-colporate and-porate —Monotropa uniflora, 6) 3- to 4- porate—Monotropastrum humile. Relationships among taxa within the Monotropoideae are illustrated on the palynological characters including the aperture type, exine sculpture and structure. Both pollen grains with two and four apertures have evolved independently from pollen grains with three apertures, according to the infraspecific variation of aperture numbers and the usual occurrence of three-aperturate pollen grains in the Ericaceae. 3-colp(oroid)ate pollen ofAllotropa is the most primitive and occupies an isolated position in the subfamily, on the other hand 3- to 4-porate pollen ofMonotropastrum humile is most advanced in the subfamily, probably even in the Ericaceae. A reduced sexine inMonotropastrum humile appears to be a specialized pollen character. Infraspecific geographical difference in palynological characters is revealed in two species ofMonotropa for the first time.M. hypopitys is basically characterized by pollen grains with two apertures in the New World vs. three apertures in the Old World.M. uniflora is basically characterized by 3-porate pollen in the New World vs. 3-colporate in the Old World. In both species pollen grains with more primitive characters usually occur in the Old World.     

Cyclical transformations of the actin cytoskeleton of hyacinth pollen subjected to recurrent vapour-phase hydration and dehydration

Summary— Transformations of the actin cytoskeleton of the pollen of Hyacinthus orientalis during cycles of vapour-phase hydration and dehydration have been examined using a non-fixation, DMSO permeabilisation method for TRITC-phalloidin staining, coupled with microwave stabilisation. In freshly shed pollen actin appears: a) at the plasmalemma in the form of extended, thin fibrils co-oriented with the cellulosic microfibrils of the contiguous intine; b) as a sheath investing the generative cell; c) as spicules around the vegetative nucleus; and d) in scattered spicules in the cytoplasm. During hydration in 85–95% relative humidity (RH), actin from all of these sites is progressively translated into a system of extended fibrils in the vegetative cell, concurrently with the onset of movement in the cytoplasm. Dehydration at 5–7% RH reverses this process, actin accumulating in rodlets, spicules or larger fusiform bodies in close association with the generative cell and vegetative nucleus, and also in the cytoplasm. The fibril system initially present at the plasmalemma is not restored. After ten cycles of hydration and dehydration 3.6% of the grains remained germinable. The ecological significance of the findings is noted, and the possibility that the observed transformations result from variation in the Ca²⁺ concentration in the cytosol as the water content of the cytosol changes is considered.     

Distyly in Polygonum jucundum Meisn. (Polygonaceae)

Pollen grains of tribe Sanguisorbeae (Rosaceae, Rosoideae) were examined using scanning electron microscopy to identify useful characters, test taxonomic and phylogenetic hypotheses among genera, and elucidate pollen character evolution based on a molecular phylogeny. Aperture number, aperture structure, pollen shape, and exine sculpturing were variable within Sanguisorbeae and were used to delineate six pollen types. Four types (I–IV) were observed only in subtribe Sanguisorbinae whereas two types (V–VI) were found only in subtribe Agrimoniinae. Pollen grains of tribe Sanguisorbeae were generally subprolate to spheroidal in shape, had operculate or pontoperculate apertures, and had three apertures, except for Margyricarpus (tetraperturate). Exine sculpturing within Sanguisorbinae represented variations of striate, verrucate, rugulate, and perforate patterns often with microechinate sculpturing. Striate exine patterns and prolate shapes characterized the pollen of the Agrimoniinae, except for the microechinate-verrucate pattern and subprolate to spheroidal shapes observed in Hagenia. Pollen characters are most useful at the generic level and, when mapped on to a molecular phylogenetic tree of the tribe, are concordant with a monophyletic Agrimoniinae and a clade comprising Margyricarpus + Acaena + Polylepis + Cliffortia + Sanguisorba in the Sanguisorbinae. Outgroup comparison indicated that operculate colpi, three apertures, and polymorphism for striate or microverrucate exines represented primitive states for tribe Sanguisorbeae.     

The ultrastructure of polymorphic pollen grains of Canna indica L.

Summary Our investigations on Canna indica L. indicate that the pollen of this species is polymorphic: there are two types of pollen — a larger type and a comparatively smaller type. Transmission electron microscopy (TEM) revealed the presence of small vacuoles containing tannic substances in the generative cell (GC) of the larger grains: the GC of the mature grain contained a higher quantity of tannins than the GC of the immature grain. Mitochondria, lipid bodies, rough endoplasmic reticulum (RER) and microtubular bundles were present in the cytoplasm of the GC. Numerous mitochondria, lipid bodies and plastids were also present in the vegetative cell (VC), with the mitochondria clustered around the vegetative nucleus. The plastids were observed to be associated with the RER cisterns. During the maturation process, the number of starch grains contained in the plastids decreased.     

Investigation on the Development of Male Cametophyte in Anemarrhena Asphodeloides

Anemarrhena asphodeloides is a monotypic genus of Liliaceae, endemic to China and Korea. This genus is characterized by possessing three stamens. From development of male gametophyte, three features of the species are noteworthy. (1) During meiosis of the micros- pore mother cells, the Golgi vesicles are immediately incorporated into the formation of the material of callose wall; The latter lying at the outer tangential is about 4 gm in thickness dining formation of the tetrad. In the outer tangential callose wall there are certain cytoplasmic canals, which are about 0.6 to 1 μm in diameter. During the development of pollen grains, there are a number of other vesicles dispersing in the cytoplasm of the microspores. The activity of these vesicles seems to be involved in accumulation and formation of lipid bodies. But the above vesicles, which were derivxed from Golgi or endoplasmic reticulum, have not been known in this genus. (2) By two-celled stage of pollen grains, the unequal distribution of lipid bodies is very prominent, and they are singular in being placed on the boundary between the plasmalemma of vegetative and generative cells. While the generative cell is delached from the intine of pollen grain, the generative cell is surrounded by the lipid bodies which had been called the corona of them. By the observation of TEM, these lipid bodies come from the cytoplasm of vegetative cell and did not remain a constant surrounding layer. Towards the stage of pollen maturation, the lipid bodies lying oppositely to the nucleus of vegetative cell were gradually dispersed in the cytoplasm. Their function is unknown but the observation shows that some of them move to the plasmalemma of the pollen grain. (3) An important feature of the mature pollen grain in Anemarrhena is that the generative cell does not contain plastids during polle development. On the basis of cytological mechanisms of the plastid inheritance, Hagemann (1983) has classified the angiosperms into four groups of species, of which the Lycopersicum type, Solanum type, and Triticum type belong to the mode of a uniparental maternal inheritance of plastids; while the Pelargonium type represents the mode of biparental inheritance of plastids. Our studies have confirmed that the mode of plastid inheritance in Anemarrhena asphodeloides is similar to Gasteria verrucosa, both show the same mode of plastid inheritance of Lycopersicum type.     

Localization and release of allergens from tapetum and pollen grains ofBetula pendula

Summary Although intact pollen grains are assumed to be the primary carrier of pollen allergens, specific immunoreactive components have been found in other aerosol fractions, e.g., starch grains and remains of tapetal cells Cryo-scanning-electron-microscopy results demonstrate the presence of a clear network of strands connecting the tapetum with the microspores. The distribution of protein in tapetal orbicules, pollen wall, and pollen cytoplasm was tested by histochemical stains for light microscopy and transmission electron microscopy. The protein is mainly localized at the apertures and starch grains in the cytoplasm of pollen and in the core and on the surface of tapetal orbicules. Monoclonal antibodies Bv-10, BIP3, and BIP4 have been used to locate the cellular sites of pollen and tapetal allergens inBetula pendula (syn.B. verrucosa). The application of rapid-freeze fixation prevented relocation of allergens from their native sites. The allergens are predominantly found in the starch grains and to lesser extent in the exine. We also tested interactions between mature birch pollen and human fluids: saliva, nostrils fluid, and eyes solution. The aim was to mimic more closely the in vivo situation during allergenic response. In all cases we observed several pollen grains that were burst and had released their cytoplasmic contents. In the nose the allergens are released from the pollen within minutes. In rhinitis, nasal pH is increased from the normal pH 6.0 to 8.0. When we used nasal fluid at pH 8.0, the number of ruptured pollen grains increased. The mechanism that might induce formation of small allergen-bearing particles from living plant cells is discussed.     

Spatial and temporal organization of actin during hydration,activation, and germination of pollen inPyrus communis L.: a population study

Summary Dynamics of F-actin organization during activation and germination ofPyrus communis (pear) pollen was examined using rhodaminephalloidin. Prior to activation, the rhodamine-phalloidin labelling pattern appeared as circular profiles in the peripheral cytoplasm of the vegetative cell and as coarse granules around the vegetative nucleus. In activated pollen, parallel arrays of cortical F-actin were aligned circumferentially, along the polar axis in non-apertural areas of the pollen grain, and at 45° to 90° to the polar axis beneath the apertures. Some pollen also showed fluorescent granules or fusiform bodies dispersed throughout the cytoplasm, but as the number of such pollen diminished with prolonged incubation, these are being considered as intermediate patterns. In later stages, the filaments became organized as interapertural bundles traversing the three apertures. However, prior to emergence of the pollen tube, labelling became confined to a single aperture. In germinated pollen grains, actin microfilaments are aligned more or less axially with respect to the axis of the developing pollen tube.The granular labelling pattern seen around the vegetative nucleus prior to pollen activation also became clearly filamentous with pollen activation; this filamentous pattern persisted until germination when it was replaced by cables that aligned longitudinally with respect to the emerging tube axis.The results demonstrate that the organization of actin undergoes considerable changes in the period preceding pollen germination and that microfilament polarization is achieved before pollen germination.     

Postmeiotic cytokinesis and pollen aperture number determination in eudicots: effect of the cleavage wall number

Summary.  In eudicot postmeiotic tetrads, apertures are usually joined in pairs in highly conserved areas. These appear to be located at the last points of contact persisting at the end of cytokinesis between the cytoplasm of the future microspores. In order to investigate the relationship between cytokinesis and aperture formation, aperture distribution within postmeiotic tetrads and the progression of meiosis were studied in Nicotiana tabacum cv. Ambalema. This variety (inbred line) produces about 85% tricolporate pollen and 15% tetracolporate pollen grains. In addition, about 7% of tetrads are composed of four equal-sized microspores and a supernumerary pseudomicrospore of small size and an equal proportion of tetrads exhibit unpaired apertures (these apertures are not joined in pairs within tetrads). Observation of cytokinesis indicates that both unpaired apertures and pseudomicrospores could result from the persistence of late communications between microsporocytes. Observations of tetrads indicate that an increase in the number of elements that are separated during cytokinesis is correlated with an increase in microspore aperture number. All data converge to support the hypothesis that aperture site determination is partly controlled by the number of walls formed to separate the different elements of the tetrad. Received May 22, 2002; accepted October 29, 2002; published online April 2, 2003 RID="*" ID="*" Correspondence and reprints: Laboratoire de Ecologie, Systematique et Evolution, Batiment 362, Université Paris Sud, 91405 Orsay cedex, France.     

Distribution of insoluble polysaccharides, neutral lipids, and proteins in the developing anthers of Campsis radicans (L.) Seem. (Bignoniaceae)

In this study, distribution of polysaccharides, lipids, and proteins in the developing anthers of Campsis radicans (L.) Seem. was examined from sporogenous cell stage to mature pollen, using cytochemical methods. To detect the distribution and dynamic changes of insoluble polysaccharides, lipid bodies, and proteins in the anthers through progressive developmental stages, semi-thin sections of anthers at different developmental stages were stained with periodic-acid-Schiff (PAS) reagent, Sudan black B, and Coomassie brilliant blue, respectively, and examined under light microscope. Ultrastructural observations with TEM were also carried out to determine the storage form of starch in the connective tissue, and storage form of lipids in the tapetal cells. In sporogenous cell stage, anther wall contains numerous insoluble polysaccharides. However, from the sporogenous cell stage to the vacuolated microspore stage, the amount of insoluble polysaccharides in the anther wall decreases gradually. At bicellular pollen stage, tapetum degenerates completely and polysaccharides are not seen in the anther wall. Lipid bodies are observed in the cytoplasm of both middle layer and tapetal cells at tetrad stage, whereas they disappear in the vacuolated microspore stage. Compared with polysaccharides, proteins are limited in the anther wall at early stages of development. During pollen development, polysaccharides, proteins, and lipid bodies are scarce in the cytoplasm of sporogenous cells, but their amount increases at premeiotic stage. From tetrad stage to bicellular pollen stage, microspore cytoplasm contains variable amount of insoluble polysaccharide grains, lipid and protein bodies. At bicellular pollen stage, plentiful amount of starch granules are stored in the cytoplasm of the pollen grains. Proteins and lipid bodies are also present in the cytoplasm.     

Variation of pollen morphology, and its implications in the phylogeny of Clematis (Ranunculaceae)

Clematis s.l. (including Archiclematis and Naravelia) is a genus of approximately 300 species with cosmopolitan distribution. The diversity of its pollen was surveyed in 162 taxa belonging to all infrageneric groups of Clematis s.l. Pollen morphology was investigated by use of scanning electron microscopy to identify useful characters, test taxonomic and systematic hypotheses, and elucidate pollen character evolution on the basis of the molecular phylogeny. Clematis pollen is small to medium (14.8–32.1?μm?×?14.2–28.7?μm), oblate to prolate (P/E?=?0.9–1.4) in shape. The apertures may be tricolpate and pantoporate sometimes with 4-zonocolpate and pantocolpate pollen grains as transitional forms. The tricolpate pollen grains are predominant and occur in all the sections of the genus, whereas pantoporate pollen grains can be found in sect. Tubulosae, sect. Viorna, sect. Viticella, and Naravelia only. Phylogenetic mapping of aperture types reveals that the pantoporate pollen type may be the apomorphy in the genus and evolved several times. The surface ornamentation in all taxa studied is similar and characterized by microechinae evenly distributed on the microperforate tectum. The size and density of spinules on the tectum vary greatly but successive in the whole genus. According to the character syndromes of the ornamentation, separating sect. Brachiata from sect. Meclatis is supported. Though pollen morphology may contribute to investigation of problematic taxa, the taxonomic value of pollen morphology is limited at the species level.     

Herbivory in Spiders: The Importance of Pollen for Orb-Weavers

Orb-weaving spiders (Araneidae) are commonly regarded as generalist insect predators but resources provided by plants such as pollen may be an important dietary supplementation. Their webs snare insect prey, but can also trap aerial plankton like pollen and fungal spores. When recycling their orb webs, the spiders may therefore also feed on adhering pollen grains or fungal spores via extraoral digestion. In this study we measured stable isotope ratios in the bodies of two araneid species (Aculepeira ceropegia and Araneus diadematus), their potential prey and pollen to determine the relative contribution of pollen to their diet. We found that about 25% of juvenile orb-weaving spiders’ diet consisted of pollen, the other 75% of flying insects, mainly small dipterans and hymenopterans. The pollen grains in our study were too large to be taken up accidentally by the spiders and had first to be digested extraorally by enzymes in an active act of consumption. Therefore, pollen can be seen as a substantial component of the spiders’ diet. This finding suggests that these spiders need to be classified as omnivores rather than pure carnivores.     

Successive microsporogenesis affects pollen aperture pattern in the tam mutant of Arabidopsis thaliana

Background and Aims

The tam (tardy asynchronous meiosis) mutant of Arabidopsis thaliana, which exhibits a modified cytokinesis with a switch from simultaneous to successive cytokinesis, was used to perform a direct test of the implication of cytokinesis in aperture-pattern ontogeny of angiosperm pollen grains. The aperture pattern corresponds to the number and arrangement of apertures (areas of the pollen wall permitting pollen tube germination) on the surface of the pollen grain.

Methods

A comparative analysis of meiosis and aperture distribution was performed in two mutant strains of arabidopsis: quartet and quartet-tam.

Key Results

While the number of apertures is not affected in the quartet-tam mutant, the arrangement of the three apertures is modified compared with the quartet, resulting in a different aperture pattern.

Conclusions

These results directly demonstrate the relationship between the type of sporocytic cytokinesis and pollen aperture-pattern ontogeny.     

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     

Pattern morphogenesis in cell walls of diatoms and pollen grains: a comparison

Summary Mechanisms acting in pattern morphogenesis in the cell walls of two distant groups of plants, pollen of spermatophytes and diatoms, are compared in order to discriminate common principles from plant group- and wall material-specific features. The exinous wall in pollen is sequentially deposited on the exocellular side of the plasmalemma, while the siliceous wall in diatoms is formed intracellularly within an expanding silica deposition vesicle (SDV) which is attached to the internal face of the plasmalemma. Two levels of patterning occur in diatom and pollen walls: the overall pattern stabilises the wall mechanically and is apparently initiated in both groups by the parent cell, and a microtubule-dependent aperture and portula pattern created by the new mitotic (diatoms) or meiotic (pollen) cells. The parent wall in diatoms, and also the callosic wall in microspores, functions as anchor surfaces for transient, species-specific patterned adhesions of the plasmalemma to these walls, involved in pattern and shape creation. Patterned adhesion and exocytosis is blocked in pollen walls where the plasmalemma is shielded by the endoplasmic reticulum at the sites of the future apertures. In diatoms, wall patterning is uncoupled from the formation of a siliceous wall per se when the SDV and its wall is formed without contact to the the plasmalemma. Conversely, a blue-print pattern laid out in advance along the plasmalemma can be found in several diatoms. This highlights the key function of the plasmalemma and its associated membrane skeleton (fibrous lamina), and its orchestrated co-operation with elements of the radial filamentous cytoskeleton (actin?) in pattern formation. The role of microtubules during generation of the overall pattern may be primarily a transport and stabilizing function. Auxiliary organelles (spacer vesicles, endoplasmic reticulum, mitochondria) involved in diatoms for shaping the SDV, and a mechanism adhering and disconnecting this SDV together with spacer organelles in a species-specifically controlled sequence to and from the plasmalemma, are unnecessary for pollen wall patterning. The precise positioning of the portula pattern in diatom walls is discussed with respect to their role as permanent anchors of the cytoplasm to its wall, and in providing spatial information for nucelar migration and the next cell division, whereas apertures in pollen are for single use only.Abbreviations AF actin filaments - C/Ca callose - CF cleavage furrow - cPL cleavage plasmalemma - DV dense vesicles - ER endoplasmic reticulum - ET epitheca - HT hypotheca - mPL folded plasmalemma - MT microtubules - MTOC microtubule organising centre - PEV primexine (matrix) vesicles - PL plasmalemma - SDV silica deposition vesicle - Si silica - SL SDV-membrane - SPV spacer vesicles Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement