The morphology and ultrastructure of Jurassic in situ ginkgoalean pollen

A fragmentary pollen organ with four to six microsporangia is discovered from the Middle Jurassic of the Irkutsk coal basin, Siberia. The in situ pollen grains are boat-shaped, monosulcate, and with a nearly psilate surface. The non-aperture ectexine is composed of a thick solid tectum, a thin infratectum, and a thin foot layer. The infratectum includes one row of small rare alveolae. The supposedly poorly preserved endexine is thin and grainy. The ectexine reduces greatly in the aperture area, where only homogeneous ectexinal patches are present over the endexine. The pollen grains under study resemble in their exine ultrastructure pollen grains of the modern Ginkgo biloba and pollen grains from dispersed seeds of a presumably ginkgoalean affinity from the Middle Jurassic of Uzbekistan. This suggests that the ginkgoalean exine ultrastructure of the modern type existed as early as the Middle Jurassic. The exine ultrastructure under study is also similar, though to lesser degree, to that of dispersed pollen grains of a presumed ginkgoalean affinity from the Cretaceous of the Russian Far East. The diversity of such a long-living group as ginkgoaleans is apparently reflected in the diversity of their exine ultrastructure. To the present knowledge, ginkgoalean pollen grains can be differentiated from similar boat-shaped monosulcate pollens by the following co-occurring characters: a thick homogeneous tectum, a thin infratectum with one row of structural elements, a thin foot layer, and an ectexine that is reduced in the aperture region to patches.     

The ultrastructure of fossil dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia,Russia

The general morphology, surface sculpturing, and exine ultrastructure have been studied in dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia. The pollen grains dominate the palynological assemblage extracted from coal deposits of the Khilok Formation in the Buryat Republic, which also contain ginkgoalean leaves of Baierella averianovii as the only constituent of the assemblage of plant megafossils. The relationship between the pollen grains and ginkgoalean leaves from this autochthonous burial is hypothesised on the basis of taphonomical analysis and palaeobiogeographical data. It is shown that the ectexine of the pollen grains includes a thick solid tectum, a thin granular infratectum and a thin foot layer; the endexine is fine-grained, slightly more electron-dense than the ectexine, and is preserved only in places. The distal aperture is formed by a thinning of the exine. No analogous ultrastructure has been described so far in fossil pollen grains of this morphotype studied ultrastructurally from in situ material. For comparison, we also studied the exine ultrastructure of pollen grains Ginkgo biloba. The fossil pollen is not identical to pollen of extant G. biloba, but shows several significant similarities in the exine ultrastructure, which does not contradict the presumable ginkgoalean affinity of the fossil pollen.     

Pollen morphology and pollen-wall proteins (localization and enzymatic activity) inSesamothamnus lugardii (Pedaliaceae)

The pollen grains ofSesamothamnus lugardii Stapf (Pedaliaceae of subdesert regions of SE tropical Africa) are associated in acalymmate tetrads (cross wall cohesion), with a tectate and perforate exine and 8–12 colpi. The pollen wall consists of an ectexine with a complete, perforate and ample tectum, columellated infratectum and clearly interrupted and fragmented foot layer. The endexine is built of scanty lamellae and granules. The intine is bistratificate, with a homogeneous, fibrillate layer (endintine or intine-2) and a heterogeneous, more lax and channeled layer (exintine or intine-1). Test for glycoprotein is particularly positive in the homogeneous internal intine and channels of external intine. On the other hand acid phosphatase has been localized in the exine and channeled external intine layers. These observations confirm the general interpretation of the distribution of wall compounds.     

美乐多（Melodorum fruticosum Lour．）花粉形态观察

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察了美乐多（Melodorum fruticosum）的花粉形态特征。美乐多花粉为球形或扁圆形的单粒花粉,外壁纹饰为微褶皱状,有点状凹陷,无任何萌发孔或萌发沟。花粉外壁由外壁外层包括覆盖层（连续）、覆盖下层、基足层（1～3层薄片层结构,偶断裂或扭曲至6～10层）和外壁内层（连续）组成。其中,覆盖下层,其厚度为整个花粉外壁厚度的1／2,为混合型结构,即小柱状和颗粒状同时存在,但以颗粒状为主。花粉内壁分为内壁外层和内壁内层,其厚度逐渐变薄。美乐多的花粉特征（单粒、无萌发孔或沟、覆盖层连续、基足层为薄片层结构、花粉外壁内层薄等）与紫玉盘族其他类群一致。     

The fine morphology of pollen grains from the pollen chamber of a supposed ginkgoalean seed from the Middle Jurassic of Uzbekistan (Angren locality)

Pollen grains of Cycadopites-type were found in the pollen chamber of a supposed ginkgoalean seed Allicospermum sp. from the Middle Jurassic deposits of Uzbekistan (Angren locality). The pollen grains were studied with help of LM, CLSM, SEM, and TEM. All pollen grains show the identical morphology and exine ultrastructure allowing us to suppose the same botanical affinity. The pollen morphological data do not contradict the ginkgoalean interpretation of the seed; therefore, the pollen grains and the seed most probably did belong to the same parent plant. The pollen grains are monosulcate, the non-apertural surface is nearly psilate, with low short elements, which are occasionally scattered over the surface or more densely distributed. The aperture and adjacent areas appear to bear more distinct sculpturing. The ectexine is composed of a prominent solid tectum, a thin infratectum, and a thin foot layer. The infratectum is formed of one row of alveolae, which are more voluminous laterally, where the ultrastructure is more easily understandable. The endexine is multilamellate, although it is evident only in some regions of stained sections. Towards the aperture the ectexine becomes gradually thinner; over the aperture no sublayers can be discerned within the ectexine. The ectexine of the apertural region repeatedly varies in thickness, reflecting a sculpturing surface of this region. The obtained data contribute to the knowledge about the exine ultrastructure of ginkgoaleans; nonetheless, a TEM study of ginkgoalean pollen grains extracted from pollen organs is still highly desirable. We also considered pluses and minuses of CLSM: it failed to substitute SEM, since the surface pattern under study was too fine, but demonstrated the general morphology of the pollen grains under study better than conventional LM. The possibility of viewing virtual sections of any area of the pollen grain was profitable for later interpretation of TEM sections. CLSM would give better results in interpreting relatively large palynological objects with distinct sculptural elements, a complicated architecture, variously arranged appendages, or possessing cameras.     

Pollen morphology and ultrastructure of selected species of Magnoliaceae

The pollen morphology and ultrastructure of 20 species, representing eight genera of the Magnoliaceae are described based on observations with light, scanning and transmission electron microscopy. The family represents a homogeneous group from a pollen morphological point of view. The pollen grains are boat-shaped with a single elongate aperture on the distal face. The tectum is usually microperforate, rarely slightly or coarsely rugulose. Columellae are often irregular, but well-developed columellae do occur in some taxa. The endexine is distinct in 14 species, but difficult to discern in the genera Parakmeria, Kmeria and Tsoongiodendron. Within the aperture zone the exine elements are reduced to a thin foot layer. The intine has three layers with many vesicular-fibrillar components and tubular extensions in intine 1. The symmetry of the pollen grains, shape, type of aperture and ultrastructure of the intine show a remarkable uniformity in the family. Nevertheless there is variety in pollen size, ornamentation and the ultrastructure of the exine. The pollen of Magnoliaceae is an example of an early trend of specialization, and supports the view that Magnoliaceae are not one of the earliest lines in the phylogeny of flowering plants.     

Comparative exine development from the post-tetrad stage in the early-divergent lineages of Ranunculales: the genera <Emphasis Type="Italic">Euptelea</Emphasis> and <Emphasis Type="Italic">Pteridophyllum</Emphasis>

Studies of pollen wall development produce a great deal of morphological data that supplies useful information regarding taxonomy and systematics. We present the exine development of Euptelea and Pteridophyllum, two taxa whose pollen wall development has never previously been studied using transmission electron microscopy. Both genera are representatives of the two earliest-diverging families of the order Ranunculales and their pollen data are important for the diagnosis of the ancestral pollen features in eudicots. Our observations show these genera are defined by having microechinate microreticulate exine ornamentation, perforate tectum, columellate morphology of the infratectum and the existence of a foot layer and endexine. The presence of lamellations is detected during the early stages of development in the nexine of both genera, especially in the apertures. Euptelea presents remains of the primexine layer during the whole maturation process, a very thin foot layer, and a laminate exinous oncus in the apertural region formed by ectexine and endexine elements. Pteridophyllum has a thicker tectum than Euptelea, a continuous foot layer and a thicker endexine. In the apertures, the exinous oncus is formed by islets and granules of endexine, in contrast to the Euptelea apertures. The secretory tapetum produces orbicules in both genera, but they have different morphology and electron-density. Comparisons with pollen data from related orders and families confirm the ancestral states for the pollen of eudicots proposed in previous studies: reticulate and echinate surfaces, columellate infractectum and a thin foot layer relative to the thickness of the ectexine. According to our observations, we propose considering the possibility of a polymorphic state for the aperture number in the ancestor of Ranunculales, and suggest the development of orbicules as the ancestral state in this order.     

Pollen morphology and ultrastructure of selected species from Annonaceae

The morphology and ultrastructure of fresh pollen from nine species, one including two varieties representing seven genera of Annonaceae are described based on observations with scanning and transmission electron microscopy. The pollen grains are elliptic with a single furrow, or disulculate. Some are globose with no visible aperture or any indication of a pole. Ornamentation is smooth, rugulate, echinate or verrucate. The tectum is usually continuous and of the same thickness over the whole grain except for the aperture zone, where the exine elements are very often imperceptible. The infratectum may be granular, or columellae and granules are mixed together. The foot layer consists of continuous or irregularly contorted foliations. The endexine is distinct and thin, and varies slightly in thickness in some species, but is vaguely distinguishable in others. The intine is two-layered and consists of an entexine with many vesicular-fibrillar components with tubular extensions, and a more homogeneous endintine. The controversy around the presence of an endexine in Annonaceae is discussed, but whether its presence is ancestral cannot be determined. Data on fresh pollen are compared with those from similar studies on dried pollen.     

Pollen wall ultrastructure and ontogeny in Heliotropium europaeum L. (Boraginaceae)

The pollen grains of Heliotropium europaeum are heterocolpate, with alternation of 3 colpori and 3 pseudocolpi. The exine is characterized by a scabrate and thick tectum, massive columellae with a granular appearance and a thick nexine. The thickening of the intine at the apertural level makes the interpretation of this zone difficult. The ontogenetic study helped to understand the ultrastructure of the exine and the apertures. The different steps are as follows. The primexine matrix is formed during the beginning of the tetrad stage; it consists of an outer thick and electron dense zone and an inner one, less dense to electrons. The tectum and the infratectum begin to form in the outer zone of the matrix, towards the middle of the tetrad stage. The infratectum consists of a network of columellae variable in thickness and oriented in different directions. The foot layer is lacking. The endexine is formed on a lamella system during the callose loss and microspore separation. The endexine becomes compact very early on its inner part. The apertures are initiated during the tetrad stage; a granulo-fibrillar oncus develops. At the free microspore stage, the oncus gets fibrillar and is bordered by endexine lamellae on its outer side and by endexine granulations on its inner one and laterally. The intine is set at the end of this stage. At the vacuolated microspore stage, the intine shows three layers: two thin, clear and homogeneous layers, one outside and the other inside, and a thick middle layer that forms the zwischenkörper, crossed by trabecula, in the apertural areas.     

Exploding pollen in Montrichardia arborescens (Araceae)

Pollen grains of Montrichardia are inaperturate with psilate ornamentation. The pollen wall is formed by a thin ectexine and an extraordinarily thick intine. In living as well as in dead pollen grains contact with water leads to a rapid swelling of the intine followed by an explosive opening of the exine. Within a few seconds a thick tube is formed, which is not the pollen tube. The pollen protoplast is situated at the tip of the tube. These intine tubes are interpreted as pollen connecting tools to keep pollen grains together and adhere them to the cuticle of the hairless pollinators.     

The Structure of Pollen Wall and Its Relation to Po41en Aggregation in Cymbidium goeringii (Rchb. F.) Rchb. F.

The pollen wall of tetrads located in different positions of a mature pollinium of Cymbidium goeringii was examined with the electron microscope, and the compositions of wall materials were also tested with different histochemical methods. In all tetrads of a pollinium, the pollen wall can be distingished into an exine and an intine, but the exine may be varied greatly according to the tetrad position in a pollenium. The part of the pollen wall (the outer wall) of the external tetrads, lying close, to the tapetum, is composed of two layers, i.e. the exine, and the intine. Theexine consists of tectum, granulate ectexine and endexine, without foot layer. The intine is cellulose in nature. In the outer wall between different groups of: tetrads and in the inner wall within an individual tetrad, the structure of ectexine becomes simple and the deposition of sporopollenin is roduced The degree of reduction of ectexine nicreases from the outer to inner tetrads in several external layers of a pollinium, and even the internal tetrads have a reduced ectexine or lack of it. The present study also demonstrates that the mechanism of pollen aggregation into a pollinium is built on a combined effect of the following features: (1) connected bridges formed' by intine between two pollens within a tetrad, (2) formation of cytoplasmic channels between two pollens within a tetrad, (3) incomplete cell wall formation within a tetrad, (4) little size of tetrads and compact arrangement of mature tetrads and (5) a sticky viscin material surrounded on the outside of a pollinium.     

Beschorneria yuccoides and Asimina triloba (L.) Dun: Examples for proximal polar germinating pollen in angiosperms

Beschorneria yuccoides (Agavaceae) microspores are arranged mostly in planar tetrads. Later on, the pollen grains of the tetrad usually fall apart, but sometimes remain loosely connected by ektexine elements. The ektexine consists of a tectum, of short columellae, and of a thin, discontinuous foot layer. An endexine is absent. The bilayered intine is without any additional thickening that would usually indicate an aperture region. From this point of view the pollen grain might be considered as omniaperturate. The pollen ornamentation is reticulate with wide lumina and robust, smooth muri.

The pollen grains show an indistinct sulcus characterised by a loose reticulate ornamentation. The sulcus is not exactly at the distal pole, but shifted towards the equator. No pollen tubes are formed regularly at the sulcus. Instead, pollen tubes are normally formed at the proximal pollen face. The proximal area, indicating a large germination field, is morphologically and functionally clearly an aperture (a germination zone); however, it does not represent a sulcus. The proximal face of all pollen grains appears as ornamented, with some exine lumps.

Asimina triloba (Annonaceae) pollen is shed in permanent planar or decussate tetrads. The distal sides are microreticulate to foveolate, and do not show an aperture; the psilate proximal sides are the germination areas of A. triloba.

The presence of apertures placed at the proximal pole was reported for distinct taxa of several angiosperm families. For Drosera, Dionaea (Droseraceae) and most probably for the diaperturate Cuphea species (Lythraceae) the existence of polar germination areas can be excluded. However, in some Annonaceae taxa with permanent tetrads (Annona cherimola, Asimina triloba) a situation similar to Beschorneria might be present, and indeed a proximal polar pollen tube is formed. Beschorneria yuccoides, Annona cherimola and Asimina triloba are unequivocal examples of angiosperm pollen with an exactly proximal aperture (germination area).     

Structure of the apertural sporoderm of pollen grains inEuphorbia andChamaesyce (Euphorbiaceae)

The tricolporate pollen grains of 38 Mediterranean and Macaronesian species ofEuphorbia L. andChamaesyce S. F. Gray have a special apertural sporoderm not found in the other taxa of theEuphorbiaceae. At the apertural margo the ectexine is thinner because of shorter columellae and the thin, fragmented or even absent foot-layer. Ectexinous granules, mixed with endexinous material, are present near the ora. The endexine is homogeneous and thickened under the colpi (at the end and at the proximity of the end of colpus). Around the ora, the endexine is granulate and lamellar with irregular cavities. The apertural intine presents a characteristic structure with thickenings running along both sides of the colpi. The arrangement and structure of these intinous thickenings depend on the distance from the ora. This special morphology of the intine is present in all taxa studied here. The genusEuphorbia is considered to be the most evolved taxon of this family. The characteristic apertural sporoderm may be an adaptative modification to different physiological conditions, so it may present an apertural mechanism which is more adapted to harmomegathic changes and thus facilitate the germination and the formation of the pollen tube.     

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF SIMMONDSIA CHINENSIS TO THE ORDER EUPHORBIALES

Pollen from Simmondsia chinensis (Simmondsiaceae) was examined in LM, SEM, and TEM. The pollen is shed as monads, triangular in shape in polar view, with a 3-porate aperture type in which the pores are large and poorly defined. The tectum is irregularly scabrate, sometimes forming minute “islands” topped with spinules. In thin section, the endexine is thickened and lamellate in the aperture regions, and narrow in the mesoporus; the foot layer is well-defined but noticeably thicker in the mesoporus; and thin columellae support an essentially complete tectum. The pollen of four genera, Buxus, Pachysandra, Sarcococca, and Styloceras, from the Buxaceae to which Simmondsia has been assigned by some authors, was also examined and illustrated. The pollen morphology of two families frequently aligned with Simmondsiaceae, Euphorbiaceae and Pandaceae, is briefly discussed. For the most part pollen morphology supports the treatment of Simmondsia as a monotypic family, Simmondsiaceae.     

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.     

Pollen structure, tetrad cohesion and pollen-connecting threads in Pseuduvaria (Annonaceae)

The structure of the pollen of 42 species of Pseuduvaria (Annonaceae) is described. The pollen is consistently inaperturate, isopolar and radially symmetrical. Four basic patterns of exine sculpturing are identified: rugulate, verrucate, scabrate and psilate. The exine stratification of one representative species, P. macrocarpa , is shown to be entirely ectexinal. The ectexine consists of a discontinuous outer tectal layer, a columellar infratectal layer, and an inner lamellar foliated foot layer; the intine is very thin and fibrillar. The pollen is invariably released as acalymmate tetrads, in which the tectum is absent from the proximal walls. The individual pollen grains within the tetrads are connected by crosswall cohesion, involving both exine and intine; this form of cohesion has not hitherto been reported in the Annonaceae. In addition, pollen grains of neighbouring tetrads are connected in two different ways, viz. short exine connections and non-sporopollenin pollen-connecting threads. Neither of these cohesion mechanisms has previously been reported for the genus. The function of the various forms of cohesion between pollen grains and tetrads in Pseuduvaria is discussed as a mechanism to enhance the efficiency of pollination by enabling the fertilization of multiple ovules following a single pollinator visit.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 69−78.     

盖裂木属两种植物花粉形态观察

利用光学显微镜、扫描电镜和透射电镜观察了盖裂木属两种Talauma gloriensis和T.mexicana的花粉形态。花粉粒具远极单萌发沟,椭圆球形,外壁较光滑或略粗糙且具小穴状雕纹。在透射电镜下,花粉外壁可分为覆盖层、柱状层和基层,外壁-2明显,且厚度不均匀。在远极面萌发沟区域,外壁逐渐减薄,最后覆盖层和柱状层消失,仅残留基层。T.gloriensis的柱状层内部空间较小,多由颗粒组成,而T.mexicana柱状层中有发育较好的小柱,与覆盖层和基层连接。     

迷果芹(\%Sphallerocarpus gracilis)和红三叶

对迷果芹(Sphallerocarpusgracilis(Bess.)K-Pol.)和红三叶(TrifoliumpratenseL.)进行了染色体计数及核型分析.迷果芹的染色体数目为2n=20,核型公式为K(2n)=2x=20=14m+4sm+2st(SAT);核型类型为2A,为较对称核型,该种植物的染色体数目及核型均为首次报道.红三叶的染色体数目有2n=14、16、28、32等类型,本研究首次报道了2n=14的核型公式为K(2n)=2x=14=2M+12m,核型类型为1B,为较原始的对称核型.     

长梗苦草花粉粒的电镜观察

通过扫描电镜和透射电镜首次对沉水植物梗苦草（Vallisneria longipedunculata)的花粉粒进行了观察,其花粉粒的细胞壁非常薄,无萌发孔,但有2－3个具有较质丝的凹穴。花粉粒细胞壁的覆盖层十分不明显。具散生的颗粒;外壁内层较为厚实,但柱状结构分化不明显,整体呈海绵状;花粉内壁较厚。在花粉粒内部,有大量的单粒和复粒的淀粉粒,但未见到半复粒。