Pollen morphology and ultrastructure of the Bennettitales: In situ pollen of Cycadeoidea

The micromorphology and ultrastructure of in situ pollen from Cycadeoidea dacotensis are described from permineralized specimens collected from the Lower Cretaceous of North America. Pollen grains are ovoid and relatively small, averaging 25 μm in length and 12 μm in width. Grains are monosulcate with the exine typically invaginated in apertural regions. Exine ornamentation ranges from punctate to psilate. The exine averages 0.73 μm in thickness and is composed of a light-staining sexine and a dark-staining nexine. The sexine consists of a thin, homogeneous tectum, typically with a well-defined inner boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genus Leguminanthus and the dispersed genus Monosulcites. In addition, the fine structure of Cycadeoidea pollen is compared to that of the gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, and Eucommiidites-type pollen-producing plants.     

STUDIES OF SEED FERN POLLEN: DEVELOPMENT OF THE EXINE IN MONOLETES (MEDULLOSALES)

Monoletes pollen extracted from the seed fern synangium Dolerotheca sclerotica Baxter illustrate four stages in the development of the sporoderm. In the first stage the grains are up to 100 μm long and possess an apparent homogeneous exine in which there is little differentiation between the nexine and sexine. Numerous nexine lamellae and the initiation of sexine expansion mark stage 2 in exine ontogeny. Further expansion of the sexine continues in the third stage until the ratio between the nexine and sexine is approximately 1:5. The final stage in maturation of the sporoderm shows an expanded alveolate sexine with some of the sporopollenin units broken and disorganized. It is at this stage of development that nexine lamellae are most prominent. The formation of sporoderm layers in the fossil grains is compared with pollen grain development in living cycads (Cycadophyta) and a model proposed to account for the apparent early formation of nexine lamellae in Monoletes. The evolution of exine components in early pollen types is discussed.     

Pollen morphology and ultrastructure of Marathrum schiedeanum (Podostemaceae)

The Podostemaceae, or river-weeds, comprise 46 genera and 270 species of dicots and are the largest family of strictly aquatic angiosperms. Despite the large size, specialized habitats, and enigmatic morphology of the family, relatively little is known about the palynology of Podostemaceae. In the current paper, pollen morphology and ultrastructure of Marathrum schiedeanum are described. Pollen grains are relatively small, spheroidal, and tricolpate to spiraperturate. The exine has a microechinate ornament, a tectate-granular sexine and a relatively thick nexine in non-apertural regions, and a semitectate sexine and thinner nexine in apertural regions. Although aperture variation occurs in the family, this is the first report of the spiral aperture type in Podostemaceae. The spiraperturate condition appears to be derived in river-weeds, as does the granular pollen wall, which represents a reduction of the typical columellae found in eudicots.     

POLLEN MORPHOLOGY AND ULTRASTRUCTURE OF THE CABOMBACEAE: CORRELATIONS WITH POLLINATION BIOLOGY

Of all species comprising the two genera of the Cabombaceae, only Brasenia schreberi J. F. Gmel. and Cabomba caroliniana Gray have been critically investigated with regard to their pollination biology. Brasenia schreberi has been shown to be anemophilous, while C. caroliniana has an entomophilous (myophilous) pollination syndrome. In the present paper, a number of pollen and pollen-related characters, including pollen size, shape, quantity, terminal settling velocity, pollen-ovule ratios, and overall exine architecture of B. schreberi and C. caroliniana are evaluated. Pollen from both species is elliptic, monosulcate, and has a tectate-columellate sporoderm with supratectal surface ornamentation. Grains of B. schreberi are small, produced in copious amounts, and settle relatively slowly. Flowers of this species have large pollen-ovule ratios. The exine of B. schreberi pollen is scabrate, relatively thin, has a uniformly thick sexine composed of a two-zoned (homogeneous/granular) tectum and distinct columellae, and a homogeneous nexine. Pollen of C. caroliniana is relatively large, produced in small quantities, and has a rapid terminal settling velocity. Flowers exhibit small pollen-ovule ratios. Exine organization of C. caroliniana pollen is typically two times thicker than that of B. schreberi; ornamentation is striate. Nonapertural sexine regions have a thick tectum and well-defined columellae, with both sexine components traversed by a dense system of channels. The nexine is relatively thin. All of the palynological characters examined correlate well with the anemophilous and entomophilous syndromes of B. schreberi and C. caroliniana, respectively. Moreover, several other parameters of exine ultrastructure from each species exhibit positive correlations with the respective pollination mechanisms, including: tectum thickness, columellae diameter, tectum-nexine ratios, and the consistency, distribution, and total amount of pollenkitt present. Overall exine ultrastructure is also discussed from a historical perspective as well as with respect to its phylogenetic significance.     

Dimorphic exine sculpturing in two distylous species ofDyerophytum (Plumbaginaceae)

Light and SEM observations on the pollen ofDyerophytum africanum andD. indicum have revealed marked differences in exine features. These distylous species also have dimorphic pollen. In the short-styled individuals of both species, the sexine and nexine are of equal thickness, and the clava-like sexinous processes are short without marked projections. In the long-styled individuals, the sexine is thicker than the nexine, the clavae are higher than broad with an apical spinule. Pollen size and apertures are identical in both morphs. — Palynological evidence is presented for relationships betweenDyerophytum andCeratostigma, Plumbago andAegialitis. Moreover, the genusDyerophytum exhibits pollen morphological similarities with some species ofLinum (Linaceae).     

西瓜花粉壁超微结构与花粉ATP酶细胞化学定位

研究了西瓜花粉壁超微结构以及单核花粉液泡化时期ATP酶活性超微细胞化学定位。花粉壁的外壁分为外层和内层 ,外层包括覆盖层、基粒棒和基足层等三层 ,内层只包含一层。外层电子密度相对较小 ,内层电子密度相对较大 ;外层与内层之间有缝隙。ATP酶活性反应产物主要分布在细胞质基质、质体、内质网和花粉内壁中     

Immunocytochemical localization of the allergenic proteins in the pollen of Cryptomeria japonica

Applying an immunocytochemical method, a localization of the protein Cry j I in the Cryptomeria japonica pollen, which is the major allergen responsible for Japanese cedar pollinosis, is investigated with the monoclonal and polyclonal antibodies produced from the protein. The protein that reacts to the polyclonal antibody localizes on the sexine, nexine, between nexine and intine layers, orbicles, cell wall of a generative cell, Golgi body and Golgi vesicles. The allergenic protein contained in the exine and orbicles of Japanese cedar pollen can diffuse or dissolve easily from there into the mucus covering of the eye and nose, causing a response in less than 1 min after exposure. Since the orbicles have a diameter of about 430 nm, they can pass easily through the pores of most protective masks to reach the sensitive tissues of the patient. The proteins react to the monoclonal antibodies (J1BO1 and J1BO7) and localize on the Golgi body, sexine, nexine and orbicles (but not between the nexine and intine layers), and on the generative cell wall. In the young pollen grain, numerous allergenic protein particles contained in the orbicles and sexine layer, but there is only a small amount of the protein between the nexine and intine layers, since the intine layer is not yet complete at this stage. More will be accumulated there during developmental maturation. The allergenic protein is also found on the tapetal materials remaining in the young anther. Since the materials forming the exine layer and orbicles come from tapetal tissue, it is assumed that some of the allergenic protein is produced in the tapetum and localized in the orbicles and pollen wall during maturation, and that the rest of the allergenic protein is produced in the Golgi body in the mature pollen grain.     

西瓜花粉壁超微结构与花粉ATP酶细胞化学定位

研究了西瓜花粉壁超微结构以及单核花粉液泡化时期ATP酶活性超微细胞化学定位。花粉壁的外壁分为外层和内层,外层包括覆盖层、基粒棒和基足层等三层,内层只包含一层。外层电子密度相对较小,内层电子密度相对较大;外层与内层之间有缝隙。ATP酶活性反应产物主要分布在细胞质基质、质体、内质网和花粉内壁中。     

A comparative study of the gradual degradation of exines,resulting from the effects of temperature

The gradual degradation of three types of pollen exines from different plant groups (gymnosperms and angiosperms) with rising temperature has been observed and comparisons made. Pollen grains are heated to different temperatures (100°C–350°C) in a sealed copper tube, placed in a nichrome wire resistance furnace. In each case the pollen grains are heated for 100 hours.The colour change and the size reduction with rising temperature are common to all pollen types. The sexine or ornamented part of the pollen exine is affected first by rising temperature. In angiosperm pollen, the sexibe pattern is not recognisable at 300°C, but pine pollen retains its pattern up to 350°C. The nexine seems to be more stable at high temperatures than the sexinous elements and either remains unaltered with remnants of the sexinous pattern, or becomes altered and amorphous.The lamellar part of the nexine appears to be important and the evolutionary significance of the exine is discussed. The present work shows that the gymnosperm pollen has more stable exines, and may be better adapted for survival than angiosperm exines.     

COMPARATIVE POLLEN MORPHOLOGY AND TAXONOMIC AFFINITIES IN CYCADALES

Scanning and transmission electron microscopy of pollen grains of 29 species, representing the ten extant genera of Cycadales, has provided valuable insight into their relationships. Pollen grains of these taxa are boat-shaped, monosulcate, and bilaterally symmetrical. They range from narrowly to widely elliptical or subcircular when viewed distally, and have an exine surface of psilate, foveolate, or fossulate. Pollen wall ultrastructure of Cycadales is typically tectate with alveolate∗∗∗spongy exine. The nexine is laminated in all genera. Nexine 1 (footlayer) is present in most species as a thin and often discontinuous layer. There is consistent variation in thickness of the sporoderm layers among the genera but relative uniformity within them. Pollen characteristics are well correlated with macro- and micromorphological features, chromosome numbers, geographical distribution, and postulated pollination mode. A close affinity between Encephalartos, Lepidozamia, and Macrozamia is recognized. Pollen characteristics of the genus Bowenia show some similarity with those of the latter group. Except for two species of Macrozamia which are narrowly elliptic, all of the genera have widely elliptic pollen and share a psilate exine surface and the thinnest sexine with nearly identical arrangement of alveoli. Pollen grains of the species in the genus Dioon exhibit a unique morphology but are more similar to Stangeria than they are to those of taxa in Zamiaceae. The circular outline of the grains and the foveolate exine surface are characters shared by these two genera, but several morphological features distinguish Dioon from Stangeria. Ceratozamia and Zamia share a widely elliptic shape, foveolate exine surface and nearly identical sexine, as well as morphological features and chromosome numbers. They differ from Microcycas in sexine thickness, gross morphology and chromosome numbers. The pollen grains of Cycas circinalis and C. revoluta differ in size and structure of the sexine from all other genera and from each other, substantiating their distinct subgeneric delimitations.     

A NEW LYGINOPTERID POLLEN ORGAN WITH ALVEOLATE POLLEN EXINES

A new lyginopterid pollen organ is described based upon specimens occurring in a single coal ball from the Providence, Kentucky locality. Seven to nine beaked sporangia are fused together at their proximal ends forming a common synangial chamber; synangia are joined together in clusters of two or three. In situ prepollen is similar to Cyclogranisporites and Verrucosisporites sporae dispersae. The thick exine has a lamellate nexine and a prominent alveolate sexine.     

含笑花药发育的超微结构研究

对含笑花药发育中的超微结构变化进行观察,结果显示:(1)花粉发育中有三次液泡变化过程——第一次是小孢子母细胞在形成时内部出现了液泡,这可能与胼胝质壁的形成有关;第二次是在小孢子母细胞减数分裂之前,细胞内壁纤维素降解区域形成液泡,它的功能可能是消化原有的纤维素细胞壁;第三次是在小孢子液泡化时期,形成的大液泡将细胞核挤到边缘,产生极性。(2)含笑花粉在小孢子早期形成花粉外壁外层,花粉外壁内层在小孢子晚期形成,而花粉内壁是在二胞花粉早期形成;花粉成熟时,表面上沉积了绒毡层细胞的降解物而形成了花粉覆盖物。研究认为,含笑花粉原外壁的形成可能与母细胞胼胝质壁有关,而由绒毡层细胞提供的孢粉素物质按一定结构建成了花粉覆盖物。     

ULTRASTRUCTURE AND DEVELOPMENT OF MESOZOIC POLLEN: CLASSOPOLLIS

Because of its complexity one of the most unusual fossil pollen types is the genus Classopollis. Grains of this broadly defined Mesozoic taxon range from the late Triassic into the Cretaceous (Turonian), and include forms that are spherical with a subequatorial rimula. On the proximal pole is a trilete mark, and on the distal surface a thin area in the sporoderm termed the cryptopore. Ultrastructural studies of Classopollis have been completed on grains extracted from the pollen cone Classostrobus comptonensis collected from the Lower Cretaceous Wealden beds on the Isle of Wight, England. The sporoderm consists of clearly defined nexine and sexine components, with the mature nexine composed of approximately 20 electron dense lamellae, each about 10 nm thick. The sexine consists of four (S_1–4) easily recognizable layers, with the most prominent zone formed of coarse, inwardly-tapering elements. The S₂ layer is uniformly thickened, except in specialized areas (e.g., trilete, rimula, cryptopore) where it becomes thin. The remaining wall layers include spinules that ornament the surface and a uniform series of small lacunae associated with the spinule bases. The presence of orbicules and a complex system of membranes associated with the grains extracted from less mature cones provides an opportunity to trace some developmental stages in Classopollis sporoderm ontogeny, and to compare these stages with those of selected extant pollen types. The functional significance of the infrastructure in Classopollis pollen is discussed.     

鹅掌楸属植物花粉萌发前后壁的超微结构

观察描述了在电镜下中国鹅掌楸（Ｌｉｒｉｏｄｅｎｄｒｏｎｃｈｉｎｅｎｓｅ）和北美鹅掌楸（Ｌ．ｔｕｌｉｐｉｆｅｒａ）２种植物花粉壁的超微结构及其水合后的变化。（１）成熟花粉壁由６层组成,即外壁３层──外层,中层１和中层２,内壁３层──内壁１,内壁２和内壁３。（２）花粉水合时,在内壁３与质膜之间由Ｐ一粒子（多糖－粒子）和被膜小泡参与形成新层。（３）花粉萌发时,由内壁３的一部分和新层突出萌发孔共同形成花粉管壁。（４）新层于花粉管形成早期分成２层──外染色深的果胶层和内电子透明的胼胝质层。     

Pollen morphology of Microstachys (Euphorbiaceae) with emphasis on neotropical species

Abstract

In Euphorbiaceae tribe Hippomaneae is the pantropical genus Microstachys, comprised by 24 species, mostly from Brazil. Palynological studies with several representatives of the genus are scarce. The purpose of this study was to describe the pollen morphology of Microstachys and find possible differentiating characteristics between its species. Ten species of the genus were analysed, represented by 21 herbarium collections. Their pollen grains were acetolysed, measured and photographed under light microscopy (LM) and scanning electron microscopy (SEM). The analysed species possess pollen in monads, of small to medium size, isopolars, amb distincticly trilobed, oblate-spheroidal, prolate-spheroidal or subprolate, tricolporate with narrow and very long colpi, almost fused at the poles sometimes forming an invagination with tapering ends and margo of the colporus wide to very wide and psilate; endoapertures lalongate to very lalongate with tapering ends, presence of a narrow costae distinct in the endoaperture; exine microreticulate homobrochate, walls with simple columella; at the mesocolpus the sexine separates from the nexine forming cavea; and sexine always thicker than the nexine. Microstachys is a stenopalynous genus, despite its species varying in pollen size, shape and width of the cavea, margo of the colporus, and length of the endoapertures, demonstrating taxonomic value, and indicating a contribution towards future systematic analyses.     

Melissiotheca: a new pteridosperm pollen organ from the Lower Carboniferous of Scotland

Melissiotheca is based on fusainized pollen organs of pteridospermous affinities which occur abundantly in an Upper Visean limestone at Kingswood, near Pettycur (Scotland). The new species is a pedicellate synangium composed of 50–150 sporangia each of which is embedded at its base in a parenchymatous cushion divided into lobes. The sporangia are fused along their proximal half but are free distally. Dehiscence is longitudinal. Each sporangium is supplied at its base by a single vascular strand. Prepollen is small, spherical and trilete with a rugulate exine. In ultrastructure, the nexine appears homogeneous; the sexine shows internal sculpture of granae and rod elements. Melissiotheca has not been assigned to any family, but it shows many affinities with pollen organs attributed to the Lyginopteridaceae.     

La sculpture et l'infrastructure du sporoderme de Ginkgo biloba comparées à celles des enveloppes polliniques des cyccadales

The Ginkgo biloba sporoderm, when examined with transmission and scanning electron microscopes, shows a sculpture and a texture which are very different from those observed in cycads.The ornamental units are “rugules” which are evenly disperesed over the pollen grain surface except on the germinal zones which is decorated with “verrucoïde” components mixed with a few ridges. (2) The exine is composed of a tripartite sexine, the middle zone of which is full of irregular pits, and of a thick and strongly lamellated nexine.     

Pollen ultrastructure in <Emphasis Type="Italic">Aristolochia manshuriensis</Emphasis> and <Emphasis Type="Italic">A. contorta</Emphasis> (Aristolochiaceae)

Pollen ultrastructure has been studied in two relict and rare species of the genus Aristolochia, A. contorta Bunge and A. manshuriensis Kom. (Aristolochiaceae). Both species have inaperturate, spheroidal, sometimes distally monocolpate or distally bicolpate pollen grains. The equatorial and polar axes of pollen grain in A. manshuriensis are 48.5 and 44.0 μm, respectively. The percentage of defective pollen grains in A. manshuriensis is 3.4%. The fossulate, perforated exine is up to 2.3 μm in thickness; the sexine and the nexine are almost equal in thickness. In A. contorta, the equatorial axis of pollen grain is 36.6 μm: the defectiveness percentage, 24.5%. The exine is verrucate, up to 0.3 μm in thickness, while the sexine is two to three times thicker than the nexine. The pollen germination experiments have shown that pollen of A. manshuriensis, in contrast to A. contorta, can germinate in 10–20% sucrose at 22°С. These data and the high percentage of pollen defectiveness in A. contorta indicate that the androecium function in this species is reduced. The reduction of the androecium function is evidenced by a small amount of pollen grains in anthers or empty anthers and a high percentage of defective pollen grains.     

A new elater-bearing Late Albian pollen species from offshore eastern Saudi Arabia

A new elater-bearing pollen referable to Elaterocolpites is described from Late Albian sediments of the Arabian Gulf, offshore eastern Saudi Arabia. This pollen has a main body consisting of five elater-like projections in the equatorial area and five colpi, one colpus at the base of each projection. The exine has three layers. The foot-layer forms the nexine whereas the other two layers, the baculate-layer and the tectum, form the sexine. The exine structure has an angiosperm affinity. The pollen occurs within the Middle Cretaceous phytogeoprovince characterized by its elater-bearing palynomorph occurrences.     

Sporoderm in Populus and Salix

Four phenomena were observed in a study of Populus tremula and P. tremula f. gigas microspores from before microspore mitosis through mature pollen which may have general significance in the ontogeny of pollen grains: 1) The exine and orbicules (Ubisch bodies) were covered by membranes. 2) The exine and the tapetal surfaces where orbicules form were covered by a polysaccharide (PAS positive) coat until after microspore mitosis; subsequently the tapetum became plasmodial. 3) Material having the staining characteristics of the nexine 2 (endexine in the sense of Fægri) accumulated on membranes in microspores in the space between the exine and the plasma membrane. That material was almost completely gone from the wall in mature pollen. The membranes on which material had accumulated migrated through the exine. Following passage through the exine these membranes were seen as empty fusiform vesicles in micrographs of anthers prepared by commonly used methods. 4) At about microspore mitosis when the cellulosic intine begins to form, microtubules about 240 A in diameter occurred near the plasma membrane and generally parallel with it. Positive acid phosphatase reactions in tapetal cells together with the morphology of orbicules and other tapetal organelles suggest that the wall of orbicules, which is like the pollen exine, may form as a residual product of a lysosome system.

Sections of mature Salix humilis pollen were compared with Populus.