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1.
The early development up to the end of gastrulation of the marineprosobranch Nassarius (Hinia) reticula-tus (Linnaeus) has beenexamined by scanning and transmission electron microscopy. Thesynchrony of the cleavage divisions ends with the formationof the second quartet. The somatoblast 2d and the mesen-toblast4d appear earlier than the other micromeres of their quartets.From the 16- to the 32-cell stage the turret cells have an outgrowth.At the end of cleavage, Nassarius shows a typical sterroblastula.During gastrulation, the epibolic encirclement of the yolk macromeresby the micromeres is produced by an active flattening of themicromere cap and at the end of gastrulation the blastoporeis completely closed. The nuclei of the four yolk macromeresmigrate from the animal cell regions towards the vegetativepole. The development of Nassarius reticulatus is very similarto that of the related species llyanassa obsoleta (Say). (Received 19 December 1990; accepted 18 August 1991)  相似文献   

2.
Protonephridia in marine streptoneuran gastropods are describedfor the first time. The organization of these paired organsof the intracapsular veliger larva of Nassarius reticulatusis described. The ciliary flame is formed by a single terminalcell. The duct is formed by one tubular cell and the aperturalcell, which forms the lips of the excretory pore. In addition,the surface of the apertural cell is covered to a great extentby the post-velar bud cell (usually termed ‘larval kidney’).Protonephridia like these are considered to be widely distributedamong streptoneuran gastropods. The homology of these organswith those of opis-thobranchs and pulmonates is suggested. Thepost-velar buds (= ‘larval kidneys’) are suggestedas a synapomorphous character of Caenogastropoda. The functionof the postvelar buds is discussed taking into considerationthe existence of a protonephridium and a possible functionalconnection between these two structures. (Received 14 June 1990; accepted 1 September 1990)  相似文献   

3.
The oesophagus of Patella vulgata Linnaeus is divisible intotwo histologically and functionally distinct regions, a centralfood channel and a series of lateral pouches forming the oesophagealglands: both are lined by a glandular ciliated columnar epithelium.Subepithelial mucous cells are restricted to the epitheliumlining the food channel and posterior section of oesophagus,whilst amylase-secreting cells occur only in the oesophagealglands. The activity of the ciliated cells lining the food channelmixes ingested food with saliva and mucus to form a food stringthat is carried towards the stomach. Amylase-secreting cellsproduce an extracellular amylase in the form of proteinaceoussecretory granules, which are released by apocrine secretionwithin cytoplasmic blebs. Release is correlated with periodsof immersion when feeding is possible. The free blebs are carriedout of the pouches and into the food channel where the amylaseinitiates carbohydrate digestion. The oesophageal epitheliumabsorbs tritiated D-glucose by a Na+-dependent mechanism inhibitedby 2,4-DNP and phloridzin and the amylase-secreting cells pinocytoseferritin. It is suggested that the oesophagus absorbs smallsolute molecules derived from ruptured algal cells and theirpartially digested polysaccharide storage products. There alsoappears to be pinocytosis of dissolved organic matter. *Current address: The R L. Weston Institute for NeurologicalStudiet, University College & Middlesex Medcal School, MortimerSt., London Wl. (Received 8 March 1988; accepted 29 April 1988)  相似文献   

4.
The composition and ultrastructure of the synergids of cotton were studied. The cells were found to be surrounded by a partial wall composed of cellulose, hemicellulose, and pectins. The structure of the wall was observed to consist of an unusual fibrillar arrangement. The filiform apparatus was demonstrated to be an extension of the wall at the micropylar end of the cell. Large amounts of ER surround the filiform apparatus. Also associated with the latter are large numbers of plastids and mitochondria. The nucleus is large and contains a single, large nucleolus and, frequently, 1 or more micronucleoli. The nuclear membrane contains membrane-bound vesicles but has few extensions into the cytoplasm. The ER is oriented parallel to the long axis of the cell and decreases in concentration from the micropylar to the chalazal end of the cell. Dictyosomes are common throughout the cell but are more numerous in the midportion where they are closely associated with the ER. The chalazal end of the cell is occupied by vacuoles rich in an inorganic compound which leaves a considerable residue of ash. Spherosome-like bodies are common throughout the cell. Both the plastids and mitochondria show evidence of division. Ribosomes are numerous and are both free and associated with the ER, nucleus, plastids, and mitochondria. The function of the synergids is proposed to be the absorption, storage, and transport of compounds from the nucellus. On the basis of this function, it is suggested that the synergids act by providing material to the egg and the developing embryo and endosperm and that they are involved in the growth of the pollen tube into the embryo sac.  相似文献   

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Rice embryo development was examined, histochemically and ultrastructurally, from the time of fertilization to embryo maturity. At the time of fertilization, the megagametophyte consists of an antipodal mass of 10–15 cells, parietally positioned along the placental side of the central cell, and, at the micropylar end, two partly fused polar nuclei and the egg apparatus. Hydrolysis of adjacent nucellar tissue suggests the secretion of hydrolytic enzymes by the antipodal mass. The antipodal cells stain intensely for RNA and protein, indicating that they are metabolically active. The egg, supported by two overarching synergids, occupies a small, wall ingrowth-lined pocket of the central cell that quickly fills with cellular endosperm after fertilization. The endosperm cells, initially supplied with nutrients from wall ingrowth-derived vesicles, are digested and utilized by the embryo as a nutritive source. The developing embryo is also supplied with assimilates via the nucellus at the base of the embryo until about 8 days after fertilization. After 8 days, the embryo is no longer connected to the nucellus, and the nucellar cells at the base of the embryo are crushed. The zygote is not structurally polarized and contains a central nucleus, amyloplasts, lipid bodies, dictyosomes and extensive dilated ER. The first division of the zygote is transverse and unequal and occurs about 4 hours after fertilization. Embryo development is rapid, and within 24 hr, the embryo consists of 5–8 cells. Organ development begins with scutellum emergence in the 3-day-old embryo. The shoot apex organizes and the coleoptile develops from scutellum tissue at 4 days postfertilization, the epiblast emerges at 5 days, and the vascular bundle and root apex differentiate by 6 days after fertilization. Starch begins to accumulate in the basal cells of the 3-day-old embryo and deposition proceeds acropetally over the next 9–10 days. Lipid accumulation begins in the basal scutellum in the 6-day-old embryo and also proceeds acropetally. Storage protein synthesis is first detected in 6-day-old embryos and accumulation again proceeds acropetally, reaching the apex of the scutellum of the 25-day-old embryo. The ultrastructure of the 24-hr-old embryo is distinctive. The cells are characterized by numerous vesicles, heterochromatin and extensive nuclear evaginations.  相似文献   

7.
The development of jack pine (Pinus banksiana Lamb.) microsporangia from October to April was investigated with a microdensitometer and a transmission electron microscope. DNA, RNA, and protein content of sporogenous cells was measured at monthly intervals. DNA was unreplicated (2C) until March when DNA synthesis was first noted, coinciding with a loss of heterochromatin. Protein content doubled in April. RNA staining increased in December and then decreased. Numerous whorls and stacks of rough endoplasmic reticulum and ribonucleoprotein-like granules appeared in December and may be related to the RNA increase. A fibrillar, light-staining region was found in the cytoplasm of the sporogenous cells from November to March. It was hydrolyzed in the presence of protease and may be a winter morphology of microfilament bundles or dictyosomes. Lipid bodies and vacuoles were abundant in the tapetum and sporangial wall cells during the winter. Observations substantiate reports that winter is not a time for cessation of development.  相似文献   

8.
The crypt cells lining the Aplysia punctata digestive tubulescomprise of three types ofcell; calcium, excretory, and thincells. The calcium cells play a role in osmoregulation, mineralstorage,exocrine secretion, iron detoxification, and excretion processes.They possess well-developed microvilli and a basal labyrinth,suggesting a role in absorption. The Golgi apparatusis involvedin the production of two main components of calcium spherules;the fibrillar materialand mineralized granules. Golgi complex,rough endoplasmic reticulum (RER), ribosomes, andaltered mitochondriaare involved in the formation of calcium spherules. Secretoryactivity isindicated by the formation of dense granules containingiron and calcium salts. Lipofuscinpigment has been found inlarge concretions which may arise from cytoplasmic areas surroundedbyendoplasmic reticulum, RER and Golgi tubules. There are threestages of excretory cells,called early, mature, and post-excretorycells. This study traces the development ofgranulofibrillarvacuoles up to the formation of the lipofuscin concretions andshows thatexcretory cells are in fact degenerating calciumcells. The fine structure of thin cells suggests thatthey areyoung calcium cells. (Received 29 December 1997; accepted 15 November 1998)  相似文献   

9.
薏苡种子的糊粉层及亚糊粉层细胞的组织化学和超微结构   总被引:1,自引:0,他引:1  
薏苡(Coixlacryma-jobi)种子的糊粉层为1层细胞,径向细胞壁内含有胞间连丝,有细胞核,冰箱内浸泡的材料,未见细胞器,室温浸泡的,则观察到很多核糖体及一些嵴不明显的线粒体。细胞内充 了大量糊粉粒及脂体,糊粉粒含蛋白质,不溶性多糖,可被TBOpH4.4染成绿色,基质内通常有1个球状体,球状体含有脂肪,但不被ABB和PAS及TBOpH4.4染色。脂体大小悬殊,随机分布。亚糊粉层细胞含有许多复合淀粉粒及小形蛋白质体。蛋白质体呈弱的PAS正反应,亦可被TBOpH4.4染成绿色,并具有同心圆坏结构,中央具核心或不具,边缘具裂隙或否。内部胚乳具很多大的简单淀粉粒,蛋白质体同心圆环结构不甚明显。对薏苡与其他禾本科植物的糊粉层细胞,糊粉粒及胚乳蛋白质体的结构进行了比较。  相似文献   

10.
The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask-shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.  相似文献   

11.
目的研究己酮可可碱(PTX)对非酒精性脂肪性肝炎(NASH)大鼠肝脏超微结构和酶组织化学的影响。方法高脂饮食建立大鼠非酒精性脂肪性肝炎模型。取SD大鼠40只,分为对照组、12w模型组、16w模型组和治疗组,每组10只。腹主动脉采血,测ALT、AST、血糖等水平。取肝组织做电镜和SDH、CCO、ATPase、LDH的酶组织化学染色。结果两个模型组均比对照组ALT、AST、血糖升高,LDL降低(P<0.05)。治疗组血糖、AST比16w模型组降低(P<0.05)。电镜显示16w模型组线粒体肿大,嵴排列紊乱,基质密度降低。治疗组结构改善。酶组织化学显示四种酶的活性16w模型组均较对照组降低(P<0.05),治疗组活性均较16w模型组升高(P<0.05)。结论NASH时存在肝细胞能量代谢障碍,经PTX治疗后能量代谢障碍得到改善。  相似文献   

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利用扫描电子显微镜和光学体视显微镜,首次对仅分布于中国新疆及毗邻中亚细亚地区的、稀见荒漠拟态昆虫--荒漠竹节虫Sceptrophasma bituberculatum(Redtenbacher)卵的外部形态和超微结构进行了观察和描述,探讨其对干旱荒漠环境的适应性结构特征.  相似文献   

15.
Two buccal mass retractor muscles of Philine are innervatedby at least 4 excitatory motoneurons, whose cell bodies liein the buccal and the cerebral ganglia. The muscle fibres respondto action potentials generated in the motoneurons or their axonswith excitatory junction potentials (ejps), each of which isfollowed by a small twitch-like contraction. Both the electricaland mechanical responses facilitate and summate with repetitivestimulation. A large ventrally located cerebral neuron (VGC) inhibits tensiondevelopment in the muscle by reducing the amplitude of the excitatoryjunction potentials from and identified buccal motoneuron. Acetylcholinereversibly depolarises and causes tonic contraction of the muscles.This action is partially antagonised by hexamethonium, whichalso blocks the ejps from two axons in the buccal and one inthe pedal nerve 9. 5-Hydroxytryptamine potentiates the ejp fromthe identified buccal motoneuron and enhances the rate of relaxation.Histamine reduces the amplitude of the presumed cholinergicbuccal nerve ejps, but does not affect the hexamethonium sensitiveejp in the pedal nerve 9. In this respect its action resemblesthat of the ventral giant cell.  相似文献   

16.
The inter-and intratubular morphological variability in thedigestive diverticula of Littorina littorea and Mytilus edulishas been investigated by planimetric procedures. Five parametershave been measured: mean epithelial thickness (MET), mean diverticularradius [MDR], mean luminal radius (MLR), MLR/MET ratio and MET/MDRratio. The results indicate that irrespective of the patternof tubule organization within the digestive diverticula (whethertubule types are clustered or not), variability between individualsis greater than that between zones of the digestive gland. Thishas implications for the design of sampling strategies in investigationsof the morphology of digestive diverticula in physiologicaland pathological studies. The variability in the epithelialthickness within diverticular sections is of minor relevancein assessing the overall condition of the digestive gland inthese studies, because variability in epithelial thickness betweentubules is significantly greater than within tubules in bothspecies. (Received 10 March 1989; accepted 16 October 1989)  相似文献   

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19.
THE ACTION OF METALDEHYDE ON THE SLUG AGRIOLIMAX RETICULATUS (MÜLLER)   总被引:1,自引:0,他引:1  
Metaldehyde both as powder and in solution can act on slugs either by contact or as a 'stomach poison'. The characteristic effects of metaldehyde poisoning were immobilization broken by outbursts of unco-ordinated muscular activity and sliming which usually resulted in severe water loss. 24 hr. after treatment with moderate doses slugs were still abnormal and rarely fed within 30 hr. of treatment. It was not possible to determine the M.L.D. with the methods used, but 0·06 nig. solid metaldehyde taken orally could be lethal to slugs of 400–800 mg. body weight. Lethal effects were produced by contact of 1 hr. with concentrations equivalent to 0·0063 mg./cm.2. Toxicity increased with rise in temperature and recovery from moderate doses was dependent on slugs being in a saturated or almost saturated atmosphere. No obvious gut lesions were found in slugs which had been dosed with or had eaten metaldehyde. Its action was not by depolymerization in the gut or body cavity. In the light of laboratory and small scale field trials it is suggested that broadcasting and spraying are the best methods of applying the material.  相似文献   

20.
The flagellar apparatus of the zoospores of Tetraedron bitridens Beck-Mannagetta and Chlorotetraedron polymorphum MacEntee, Bold et Archibald includes directly opposed basal bodies, a distal fiber that is elaborated into a ribbed structure to which the continuous striated microtubule-associated component (SMAC) is connected, and partial caps over the proximal end of each basal body. The angle between basal bodies ranges from approximately 25° to 150°. Basal bodies at wider angles are interconnected via their cores. A septum is present in the B-tubule of one basal body triplet in C. polymorphum. Both organisms have four microtubular rootlets arranged in a cruciate pattern. The two X-membered rootlets in a single cell have dissimilar numbers of microtubules. In C. polymorphum there are 5 and 6 microtubules in a 4/1 and 5/1 arrangement. 3/1 and 4/1 rootlets are present in T. bitridens. Zoospores of T. bitridens have a fuzzy coat whereas those of C. polymorphum are naked. Pyrenoids in both species are covered by a continuous starch sheath. Vegetative, interphase cells of C. polymorphum have two centrioles connected by a fiber that are located in depressions in the nuclear envelope. We propose that these two genera may be closely related to Neochloris, and that the coenobial genera Hydrodictyon, Pediastrum and Sorastrum are derived from a Tetraedron-like alga.  相似文献   

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