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。     

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     

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。     

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 Development and Quantitative Cytochemistry of Exine and Intine Enzymes in Sunflower, Helianthus annuus L

High resolution cytochemical methods have been used to characterizepollen development and pollen-wall structure in Helianthus annuus.Aniline-blue fluorescent material, presumably callose, was detectedin the nexine layer throughout its development. It was associatedwith acid phosphatase activity, while the outer sexine possessedintense esterase activity during the young spore period. Acidphosphatase and esterase were present in both intine and exinewall sites in contrast to their specific location in other pollentypes. Quantitative cytochemical estimates of enzyme activityduring development reveal esterase patterns typical of gametophyticsynthesis, while acid phosphatase patterns are characteristicof sporophytic origin suggesting tapetal transfer during thevacuolate period. Helianthus annuus L, sunflower, pollen development, exine enzymes, intine enzymes, quantitative cytochemistry     

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.     

POLLEN WALL AND TAPETAL ORBICULAR WALL DEVELOPMENT IN SORGHUM BICOLOR (GRAMINEAE)

Pollen wall development in Sorghum bicolor is morphologically and temporally paralleled by the formation of a prominent orbicular wall on the inner tangential surface of the tapetum. In the late tetrad stage, a thin, nearly uniform primexine forms around each microspore (except at the pore site) beneath the intact callose; concurrently, small spherical bodies (pro-orbicules) appear between the undulate tapetal plasmalemma and the disappearing tapetal primary wall. Within the primexine, differentially staining loci appear, which only develop into young bacula as the callose disappears. Thus, microspore walls are devoid of a visible exine pattern when released from tetrads. Afterwards, sporopollenin accumulates simultaneously on the primexine and bacula, forming the exine, and on the pro-orbicules, forming orbicules. Channels develop in the tectum and nexine, and both layers thicken to complete the microspore exine. Channeled sporopollenin also accumulates on the orbicules. A prominent sporopollenin reticulum interconnects the individual orbicules to produce an orbicular wall; this wall persists even after the tapetal protoplasts degenerate and after anthesis. While the pollen grains become engorged with reserves, a thick intine, containing conspicuous cytoplasmic channels, forms beneath the exine. Fibrous material collects beneath the orbicular wall. The parallel development and morphological similarities between the tapetal and pollen walls are discussed.     

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.     

THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.     

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).     

Microsporogenesis inPinus sylvestris L. VIII. Tapetal and late pollen grain development

This last portion of our developmental study ofPinus sylvestris L. pollen grains extends from just prior to the first microspore mitosis to the microsporangial dehiscence preparatory to pollen shedding. In nine years of collecting each day the duration of the above period was 7 to 11 days. Tapetal cells extended into the loculus and embraced microspores during the initial part of the above period. Thereafter tapetal cells receded, became parallel to parietal cells and so imbricated that there appeared to be two or three layers of tapetal cells. Tapetal cells were present up to the day before pollen shedding, but only rER and some mitochondria appeared to be in good condition at that time. A callosic layer (outer intine) was initiated under the endexine before microspore mitosis. After the first mitosis the first prothallial cell migrated to the proximal wall and was covered on the side next to the pollen cytoplasm by a thin wall joining the thick outer intine. There are plasmodesmata between pollen cytoplasm and the prothallial cell. After the second mitosis the second prothallial cell became enveloped by the outer intine. The inner intine appears after formation of the two prothallial cells but before the third mitosis. During this two-prothallial cell period before the third mitosis, plastids had large and complex fibrillar assemblies shown to be modified starch grains. After the third mitosis plastids of the pollen cytoplasm contained starch and the generative cell (antheridial initial), the product of that mitosis, is enveloped by the inner intine. On the day of pollen shedding cells are removed from the microsporangial wall by what appears to be focal autolysis. The tapetal and endothecial cells for 10–15 µm on each side of the dehiscence slit are completely removed. One or more epidermal cells are lysed, but both a thin cuticle and the very thin sporopollenin-containing peritapetal membrane remain attached to the undamaged epidermal cells bordering the dehiscence slit. Our study terminates on the day of pollen shedding with mature pollen still within the open microsporangium. At that time there is no longer a clear morphological distinction between the outer and inner intine but, judging by stain reactions, there is a chemical difference. The exine of shed pollen grains was found to be covered by small spinules on the inner surface of alveoli. These had the same spacing as the Sporopollenin Acceptor Particles (SAPs) associated with exine initiation and growth.     

水稻花药发育过程中腺苷三磷酸酶的分布

水稻花粉母细胞中的ATP酶反应颗粒很少,主要分布在细胞核中。组成花药药壁的4层细胞中只有绒毡层细胞核中有较多的ATP酶。减数分裂后,绒毡层细胞质中分化出许多内质网片层,但ATP酶反应颗粒仍很少,其它3层药壁细胞中质膜ATP酶明显增加。在花粉内、外壁中形成了大量的ATP酶反应颗粒,但花粉外壁在小孢子时期形成,ATP酶反应颗粒来自绒毡层细胞的鸟氏体。花粉内壁在二胞花粉时期形成,其中的ATP酶反应颗粒来自花粉营养细胞。二胞花粉的营养细胞比生殖细胞含有更多的ATP酶反应颗粒。     

SPORE DEVELOPMENT IN THE LIVERWORT RICCARDIA PINGUIS

The ontogeny of spores of the liverwort Riccardia pinguis was studied at the light and electron microscope levels. Three stages of development were arbitrarily defined: spore mother cell (SMC); early tetrad with nonpigmented and unsculptured walls; and mature tetrad with pigmented and sculptured spore walls. The SMC is quadrilobed with a two-layered SMC wall, containing a central nucleus, many chloroplasts, spherosomes, and other organelles. During and following meiosis cell plates form from coalescing Golgi vesicles. These plates by continued coalescence eventually form a septum, completing the tetrad. This septum comprises middle lamella and primexine; within the latter the exine forms. By continued addition of vesicle contents to the septum and dorsal surfaces of the tetrad, the exine (sexine and nexine) and intine layers of the spore wall are laid down. The contents of the vesicles change successively during wall formation, corresponding to the different wall layers being formed. It is concluded that wall formation is under the exclusive control of the spore protoplast, and that the pattern of the mature exine is determined by the primexine. Rearrangement of organelles and other cellular components during sporogenesis is described.     

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.     

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     

云南松花粉形态研究

在云南松(Pinus yunnanensis Fr.)小孢子发生发育过程中,花粉母细胞、四分孢子及花粉粒均见有粘连现象。花粉气囊的形态、大小变化复杂多样。除一般具两个正常气囊的花粉粒外,还观察到气囊不发育、具一个气囊、二个异形气囊、三个气囊和四个气囊的花粉粒。成熟花粉壁从外至内可分为外壁外层、外壁内层、内壁外层和内壁内层,它们的构成成分及形态均有明显差别。贮存后花粉的内壁结构发生了明显变化。     

Pollen morphology supports the transfer of Wendlandia (Rubiaceae) out of Rondeletieae

Pollen morphology of 27 species, eight subspecies and one variety of Wendlandia was studied using scanning electron microscopy (SEM). Wendlandia pollen are monads, radiosymmetric, small in size, tricolporate (rarely tetracolporate or bicolporate) and spheroidal (rarely subprolate or suboblate) in equatorial view. The compound aperture consists of ectocolpus, mesoporus and endocolpus. In addition, reticulate sexine and granular nexine were observed. The pollen wall ultrastructure of two Wendlandia spp. was examined by transmission electron microscopy (TEM). The exine consists of the tectum, columellae, foot layer and endexine. The endexine is thickened into a costa around the aperture. The intine forms a protruding oncus at the aperture. The palynological characters show a remarkable uniformity among the Wendlandia spp. Differences with Rondeletia, the main genus of tribe Rondeletieae, exist in the exine pattern, the endoaperture and the pollen wall structure. Our observations indicated that the endoaperture type and the structure of the pollen wall of Wendlandia were similar to those of the Gardenieae–Pavetteae–Coffeeae–Octotropideae clade, which provided palynological evidence for a closer relationship of Wendlandia to subfamily Ixoroideae and the transfer of Wendlandia out of Rondeletieae. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 128–141.     

The pollinium ofLoroglossum hircinum (Orchidaceae) between pollination and pollen tube emission

The structure of the massulae composing the pollinium ofLoroglossum hircinum was studied before pollination and 12 and 24 hours afterwards. The grains are grouped in tetrads closely packed in massulae. The exine is only present on the outside of the massulae. The intine consists of two layers: a compact layer surrounding the pollen grain and a looser layer surrounding the pollen grain and a looser layer surrounding the tetrad. Twelve hours after pollination, pollen volume and the space between the tetrads increase due to vacuolization. Twenty-four hours after pollination, pollen volume and tetrad spacing are higher due to vacuolization and some grains have emitted pollen tubes. Pollen growth due to vacuole formation, and the absence of common walls between adjacent tetrads lead to crumbling of the massulae. The mature pollen grain does not have apertures: the site of pollen tube emission is determined after pollination. The first grains to germinate are those in the centre of the massula. The vegetative cell nucleus is the first to enter the pollen tube; the generative cell elongates and undergoes the second haploid mitosis shortly after entering the pollen tube.     

The wall ofPinus sylvestris L. pollen tubes

Summary The wall ofPinus sylvestris pollen and pollen tubes was studied by electron microscopy after both rapid-freeze fixation and freeze-substitution (RF-FS) and chemical fixation. Fluorescent probes and antibodies (JIM7 and JIM5) were used to study the distribution of esterified pectin, acidic pectin and callose. The wall texture was studied on shadow-casted whole mounts of pollen tubes after extraction of the wall matrix. The results were compared to current data of angiosperms. TheP. sylvestris pollen wall consists of a sculptured and a nonsculptured exine. The intine consists of a striated outer layer, that stretches partly over the pollen tube wall at the germination side, and a striated inner layer, which is continuous with the pollen tube wall and is likely to be partly deposited after germination. Variable amounts of callose are present in the entire intine. No esterified pectin is detected in the intine and acidic pectin is present in the outer intine layer only. The wall of the antheridial cell contains callose, but no pectin is detectable. The wall between antheridial and tube cell contains numerous plasmodesmata and is bordered by coated pits, indicating intensive communication with the tube cell. Callose and esterified pectin are present in the tip and the younger parts of the pollen tubes, but both ultimately disappear from the tube. Sometimes traces in the form of bands remain present. No acidic pectin is detected in either tip or tube. The wall of the pollen tube tip has a homogenous appearance, but gradually attains a fibrillar character at aging, perhaps because of the disappearance of callose and pectin. No secondary wall formation or callose lining can be seen wilh the electron microscope. The densily of the cellulose microfibrils (CMF) is much lower in the tip than in the tube. Both show CMF in all but axial and nontransverse orientations. In conclusion,P. sylvestris and angiosperm pollen tubes share the presence of esterified pectin in the tip, the oblique orientations of the CMF, and the gradual differentiation of the pollen tube wall, indicating a possible relation to tip growth. The presence of acidic pectin and the deposition of a secondary-wall or callose layer in angiosperms but not inP. sylvestris indicales that these characteristics are not related to tip growth, but probably represent adaptations to the fast and intrastylar growth of angiosperms.Abbreviations CMF cellulose microfibrils - II inner intine - NE nonsculptured exine - OI outer intine - RF-FS rapid-freeze fixation freeze-substitution - SE sculptured exine - SER smooth endoplasmic reliculum - SV secretory vesicles     

Microsporogenesis and microgametogenesis of the Argentinian species of Podocarpus (Podocarpaceae)

The development of the microsporangium and male gametophyte of three species of Podocarpus was studied with light microscopy (LM) and the morphology of pollen with scanning and transmission electron microscopy (SEM and TEM). During early stages, the male cone is covered with coriaceous scales. The archesporid cells go through a dormant period. Later the pollen mother cells differentiate and undergo meiosis. Callose is detected around the tetrad and between each monad. The microspore nucleus divides several times to give rise to a multicellular gametophyte, which includes the tube cell, the stalk and body cells, and four prothallial cells. The exine of the pollen grain is rugulate in the corpus and quite smooth in the sacci. The ultrastructure of the pollen wall consists of the alveolate sexine, the laminate nexine I and the amorphous nexine II. The intine is very thin. Comparison of the mature grain of some fossils with living members of the Podocarpaceae reveals great similarity.