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     

Ontogeny of pollen in Poinciana (Leguminoseae). II. Microspore and pollen grain periods

Our interpretations for development of exine form in Poinciana gilliesii Hooker are correlated with information, published separately, on the initiation and sequence of development of the exine template. The exine develops exactly in accordance with the template in the following respects: attachment position of foot layer rods, size of the rod components of the foot layer, size of tectal components on the aperture, height of bacules both on aperture and interaperture, and craggy inner surface of the interapertural tectum. Thickness of the interapertural tectum increased after the tetrad period, and the entire endexine was formed only subsequently.The endexine, we find, consists of tubules. The central core of these tubules is low in contrast and has a diameter similar to the thickness of the “white line lamellation” common for these endexine components as seen in oblique and longitudinal views.The bacules over the entire exine, including the extensive synaperture and its prominent margin, are all about the same height. The synaperture is marvellously adapted to accommodate contraction and expansion. Each bacule is cross-connected at the top by tectal straps long enough for rather great separation of neighboring bacules and flexible enough to be folded for close packing of bacules. At their base bacules are attached to one or several rods of the endexine. These rods are either entirely separate or can become separated over apertures.     

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。     

Microspore and tapetal development in Echinodorus cordifolìus (Alismaceae)

In the microspore tetrad period the exine begins as rods that originate from the plasma membrane. These rods are exine units that on further development become columellae as well as part of the tectum, foot layer and “transitory endexine”. The primexine matrix is very thin in the future sites of the pores. At these sites the plasma membrane and its surface coating (glycocalyx) are without exine units and adjacent to the callose envelope. The exine around the aperture margin is characterized by units of reduced height. After the exine units and primexine matrix have become ca 0.2 μm in height a fibrillar zone forms under the aperture margin. It is the exine units around the aperture that are templates for exine processes on apertures of mature pollen. Oblique sections of the early exine show that the tectum consists of the distal portions of close-packed exine units. The exine enlarges in the free microspore period but initially its substructure (tectum, columellae, foot layer and transitory endexine) is not homogeneous and unit structures are visible until after the vacuolate microspore period. There are indications of a commissural line/plane (junction plane) which separates the foot layer from the endexine during early development. Our observations of development in Echinodorus pollen extend a growing number of reports of “transitory endexines” in monocot pollen. The exine unit-structures become 0.2 μm or more in diameter and many columellae are composed of only one exine unit. Spinules become exceptionally tall, many protruding ca 0.7 μm above the level of the tectum as units only ca 0.1 μm in diameter. The outer portion of the tectum fills in around spinules and by maturity they are microechinate with their bases spread out to ca 1 μm or more. Unit structures can be seen with SEM in mature pollen following oxidation by plasma ashing and in the tapetum these units are arranged both radially, as in spinules, and parallel with the tapetal surfaces. There are clear indications of such an arrangement of units in untreated fresh pollen. Units comprising the basal part of the exine are not completely fused by sporopollenin accumulated during development. This would seem to be a characteristic feature, based on published work, of the alismacean pollen. Our use of a tracer shows, however, that there is considerable space within or between exine structure of mature Echinodorus pollen. Based upon the ca 0.1 μm size of exine-units formed early in development and exine components seen after oxidative treatment it seems that the early (primary) accumulated sporopollenin has greater resistance to oxidation than sporopollenin added, secondarily, around and between units later in development. Both primarily and secondarily accumulated sporopollenin are resistant to acetolysis but published work indicates that acetolysis alters exine material. At the microspore tetrad time and until the vacuolate stages tapetal cells are arranged as in secretory tapetums. During early microspore stages there are orbicules at the inner surface of tapetal cells. At free microspore period tapetal cells greatly elongate into the loculus and surround the microspores. By the end of the microspore vacuolate period tapetal cells release their cellular contents and microspores are for a time enveloped by tapetal organelles and translocation material.     

A Comparative study on pollen exine ultrastructure of Nothofagus and the other genera of Fagaceae

The genus Nothofagus is mainly distributed in South America and New Zealand. The present paper describes its pollen exine ultrastructure and compares the exine ultrastructure with that of the other genera of Fagaceae. The pollen grains were examined using ultrathin sectioning technique under transmission electron microscope. The study shows that the pollen exine ultrastructure of Nothofagus differs from that of the other genera of Fagaceae by its exine structure and thickness, type of aperture, and ornamentation. The pollen exine of Nothofagus is thin and possesses granular bacules, regular foot layer and tectum, spinulate ornamentation, and the endexine is usually visible at poral area, and 5～8 colpate. The pollen exine of the other genera of Fagaceae possesses entire bacules, irregular foot layer and tectum, granulate and tuberculate ornamentation, thicker endexine, and is 3-colporate ( 3-colpate or 3-colporoidate). The pollen exine ultrastructure of Nothofagus may belong to primitive type. The pollen exine ultrastructure data support Kuprianova’s opinion that Nothofagus should be separated from Fagaceae and established as a monogenetic family, i.e. Nothofa-gaceae.     

Exine and tapetum development in Symphytum officinale (Boraginaceae). Exine substructure and its interpretation

After detailing the exine ontogeny, our purpose was to find out whether the sequence of sporoderm developmental events corresponds to self-assembling micellar mesophases, initiated by genomically determined physicochemical parameters and induced by surfactant glycoproteins at increasing concentrations. Indeed, a scaffolding of the future exine, i.e., the glycocalyx, initiates with scattered clots, which then appear as clusters of spherical and worm-like micelles, derived from surface-active glycoproteins. At the middle tetrad stage, a continuous layer of the glycocalyx emerges, consisting of parallel, tightly packed cylinder-like units, which we interpret as a layer of cylindrical micelles, the so-called middle mesophase. These units bear dark-contrasted particles, arranged in strings or columns. These sites of the glycocalyx units?Cmicelles accumulate initial sporopollenin, hence the term ??sporopollenin acceptor particles?? (SAPs). This process leads to the appearance of procolumellae at the late tetrad stage. The glycocalyx units are rooted into callose and into the microspore cytoplasm. After formation of the tectum and the foot layer, the endexine initiates as a thin layer, and the latter develops into a very thick layer in the post-tetrad period. When callose disintegrates, ??bouquets?? of SAPs become evident on the tectum, which were evidently hidden inside the callose layer; these structures self-assemble into supratectal gemmae. An unusual, ??hybrid?? type of tapetum was observed. What is observed in Symphytum exine development allows us to obtain more evidence for the hypothesis of the participation of micellar self-assembly in sporoderm development and to bring together the concepts of micelles and of SAPs.     

A Study on Pollen Morphology and Ultrastructure of Subfamily Castaneoideae (Fagaceae) in China

The present paper describes the pollen morphology of 45 species of the subfamily Castaneoifeae (including genera Castanea, Castanopsis and Lithocarpus) from China. The pollen grains were all examined with light microscope, scanning electron microscope and transmission electron microscope. Pollen grains of the subfamily are prolate, subprolate or perprolate, (14.7-23.1)× (8.4 -18.9) μm in size, 3-colporate, the exine in 2-layered, 0.9-1.9μm thick, indistinctly ornate, striate-rugulose or crass-striate, sexine and nexine almost equal in thickness, the sexine consists of tectum, bacules and endonexine under TEM. On the basis of very similar pollen shape, pollen size, type of aperture and exine structure and also other characteristics of plant morphology of the genera Castanea, Castanopsis and Lithocarpus, the present authors tend to support the opinion that they all fall into the samesubfamily, Castaneoideae.     

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.     

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。     

Pollen wall development in Eucommia ulmoides (Eucommiaceae)

In Eucommia the foot layer plays a prominent part in microspore wall development. Bacules (>100 nm) are rods originating within the foot layer. Small bacules (diameter ca. 10 nm) form at the same time as the foot layer. The tectum is considered to be made up of these microbacular rods. Spinules ar continuous with the bacules. An endexine is differentiated during a middle to late microspore stage. Except for the pore the furrow includes tectum and foot layer on the endexine. Since the furrow consists of a region of reduced foot layer and the reduction is gradual near the polar ends of furrows, assessment of furrow length depends to some extent upon variations in exine infolding. The pore is well defined, but, because it is crossed by lamellations of the endexine and foot layer and often overlaid by tongues and bridges of foot layer plus tectum (including spinules) it is obscured from view using either light microscopy or scanning electron microscopy.     

Microsporogenesis in Pinus sylvestris. VI. Exine and tapetal development during the tetrad period

Coverage is of microspore tetrad period from end of cytokinesis to introduction of endexine in Pinus sylvestris. The ectexine of aperture, cap zone and sacci and the endexine are initiated while microspores are in the tetrad condition and enveloped in callose. Ectexine patterning including considerable expansion of sacci develops prior to the initiation of the endexine. Alveoli, sacci and alveoli within sacci are initiated by cytoplasmic invaginations which are sites of uptake of cell surface coat (glycocalyx) along with nutrients bound to the glycocalyx. Applications of tracers show that glycocalyx elements bind to cations and transport them to the cytoplasm. From the beginning of exine formation these invaginations are largest in the regions of future sacci and very small in the aperture. As growth progresses cytoplasm surrounding invaginations partially retracts, but callose contact is retained. Thus, these invaginations become callose covered hemispheroids (alveoli) that are “open” to the cell surface proximally and covered by callose distally but only partially so at the sides of the “cup‐shaped” alveoli. Until introduction of the endexine part of the alveolar‐sides are made up of cytoplasmic protrusions which contact the callose protrusions, even across sacci expanded more than 3 μm. Glycocalyx elements become aligned on the inner surface of the callosic alveoli and are sites for sporopollenin accumulation. The template for endexine components consists of glycocalyx elements that become aligned near the plasma membrane. Our observations indicate that uptake from the loculus to the microspore cytoplasm changes after introduction of the endexine. Henceforth, uptake is assisted by the endexine, as shown by tracers. Tapetal cells undergo two periods of hyperactivity during the period covered. Hyperactivity took place at the beginning of uptake by microspores and during endexine formation. The extra tapetal lamellation and its tapetal markers begin to exhibit the intense staining, after endexine initiation.     

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.     

THE GLYCOCALYX AND INITIATION OF EXINE SPINULES ON MICROSPORES OF CANNA

Spinules of Carina generalis pollen are initiated within a tridimensional network during the microspore tetrad period. The network is stained selectively with the hydrazide-silver proteinate method of Thiéry following periodate oxidation and by phosphotungstic acid at low pH, demonstrating the presence of polyanions. Protein is indicated as a component of the network by positive staining with PTA in acetone. These results suggest the presence of polysaccharides and proteins, possibly as mucopolysaccharides or glycoproteins. The network may be considered as a part of the glycocalyx because of its composition and association with the plasma membrane. Sporopollenin accumulates on the tridimensional network or in meshes of the net. The beaded fine structure of spinules resists the acetolysis mixture of Erdtman. Our results imply that the plasma membrane and its glycocalyx are part of the system which mediates genetic expression of exine form. The implication is compatible with formation of specific exines on all pollen grains of a plant and on aborted microspores, diminutive spores with depauperate chromosome complements, and enucleate bodies of cytoplasm resulting from meiotic abnormalities.     

POLLEN GRAIN DEVELOPMENT AND TAPETAL CHANGES IN STRELITZIA REGINAE (STRELITZIACEAE)

The proexine that forms within the callosic envelope before the end of the microspore tetrad period is thick (about 1 μm) and exceptionally complex. It has components equatable with tectum, columellae, and a nexine that includes lamellar zones. All these components persist in the exine although late in development they become difficult to recognize because this exine is reduced in thickness, apparently by stretching, to a maximum of 0.2 μm. Strelitzia is an example of an exine template, with receptors for sporopollenin, that is not maintained during development. The Strelitzia microspore surface changes from an exine like that on an interaperture sector to the channeled intinelike system common for the apertures of pollen grains. The exine on sterile grains gives what may be a rare view of a stabilized immature exine. The mature exine on viable pollen grains resembles this early exine only in the most impressionistic way. Tapetal cells go through at least one cycle of hyperactivity, dedifferentiation, mitosis, and then again hyperactivity before they finally decline.     

Exine development in Nymphaea colorata (Nymphaeaceae)

We show a sequence of developmental events in microspores and tapetal cells in Nymphaea colorata based upon transmission and scanning electron microscopic observations. There are parallel cytoplasmic processes and surface coatings in microspores and tapetal cells. Uptake is indicated by the passage of lanthanum as a tracer from anther locule into the microspore cytoplasm and by the condition of the cytoplasmic surface of microspores. The callose envelope is not a barrier to transfer of lanthanum. During formation of the proexine glycocalyx tiny spiral elements, components of the exine substructural units, were oriented in different directions in the surface coating of microspores and tapetum. Lipoidal globules are associated with the spiral elements. After the uniform proexine stage, three regions of different exine structure and their gradations become differentiated in the sporoderm: 1) a proximal region with thick tectum and foot layer, thin columellae and a compact layer of lamellated endexine; 2) a distal pole region with separately disposed endexine lamellae; and 3) an equatorial encircling-sulcate aperture region which consists of infratectal layer, foot layer, and endexine lamellae. Based upon the presence of structurally comparable surface coats in microspores and tapetal cells, experimental uptake of lanthanum nitrate, and the co-ordinated processes in tapetum and microspores, we conclude that there is probably a reciprocal controlling influence between the microspores and the tapetum and other sporophytic tissues.     

Tapetal Cell Changes and Sporoderm Development in Rhigozum trichotomum (Burch.)

Rhigozum trichotomum is a perrenial woody shrub which is indigenousto the arid regions of southern Africa. Primexine developmentis initiated while the microspores are still enclosed by callose.This is followed by the appearance of probacula which give riseto the tectum, bacula and nexine. At the time of callose dissolution,the exine pattern is well established and intine developmenthas been initiated. During the tetrad stage, the protoplastsof the tapetal cells exhibit shrinkage while conspicuous stacksof rough endoplasmic reticulum become evident in their cytoplasm.These stacks produce numerous vesicles which are associatedwith lipid globules and which migrate to the tapetal/locularwall where, it is suggested, they give rise to the pro-orbicules.The pro-orbicules become coated with an osmiophilic substance,probably sporopollenin, and are released into the thecal fluidto become intimately bound to the exine, Here they are strippedof the osmiophilic layers which appear to be incorporated intothe sporoderm. Rhigozum trichotomum (Burch.), sporoderm, pollen wall, exine, orbicules, pro-orbicules, sporopollenin, tapetum     

EXINE DEVELOPMENT IN GERBERA JAMESONII (ASTERACEAE: MUTISIEAE)

The development of the pollen wall in Gerbera jamesonii was studied using light and electron microscopy and histochemical stains. The primexine is patterned while the microspores are encased in the special cell wall. Bacules form at projections of the plasma membrane. Numerous ribosomes and large, single-membrane bound vesicles containing fibrillar material are observed near the developing bacule bases. The tectum and nonhomogeneous layer form simultaneously with the bacules, but do not appear to be outgrowths of them. Following dissolution of the callose cell wall, the lamellate exine-2 is laid down beginning in the apertural region. Polysaccharides are associated with the developing exine-1 and the pore regions of the exine-2. After exine-2 deposition, the exine-1 thickens by the addition of sporopollenin. When the exine is completed, a vacuole forms which displaces the nucleus, compresses the exine-2 and expands the incurved exine-1. As the vacuole shrinks, the intine and storage polysaccharides form.     

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.     

EXINE PATTERN FORMATION BY PLASMA MEMBRANE IN BOUGAINVILLEA SPECTABILIS WILLD. (NYCTAGINACEAE)

Transmission and scanning electron microscopy of exine development in Bougainvillea spectabilis (Nyctaginaceae) confirmed that the exine pattern is initiated by invagination of the microspore plasma membrane at the early tetrad stage. Invaginated plasma membranes take the form of a reticulate pattern that corresponds to the mature exine tectum. Protectum is the first exine layer to be deposited on the reticulate-patterned plasma membrane. Subsequently, probacules elongate basally on protruding sites of the plasma membrane under the protectum and in the lumina. These sites retreat as the probacules elongate. After the dissolution of the callose wall, a foot layer forms through the accumulation of lamellated structures. Clearly, the plasma membrane serves a determinative role in the initial pattern formation of exine.     

Three-dimensional aspects of EXINE INITIATION AND DEVELOPMENT IN LILIUM LONGIFLORUM (Liliaceae)

Pollen development in Lilium longiflorum was reinvestigated with high resolution scanning electron microscopy, with special attention to three-dimensional conformation in the exine pattern formation. At the early tetrad stage, the invaginated plasma membrane takes the form of a reticulate pattern that corresponds to the mature exine tectum. Protectum is the first exine layer to be deposited on the reticulate-patterned plasma membrane. The initial protectum consists of aggregated fibrous threads and granules. Subsequently, probacules are formed under the protectum on the plasma membrane. At the free microspore stage the developing exine becomes further enlarged and the protectum develops into mature verrucate muri. The present three-dimensional investigation conflicts with the previous studies on exine development in Lilium.