大乳头水螅基盘再生进程中过氧化物酶的表达

目的观察大乳头水螅(Hydra magnipapillata)基盘再生进程中基盘过氧化物酶的表达情况,探讨水螅基盘过氧化物酶的生理作用。方法通过ABTS细胞化学染色法显示水螅基盘过氧化物酶的表达。结果水螅基盘再生20h后其基盘过氧化物酶开始出现少量表达,其后过氧化物酶表达量逐渐增加;基盘再生52h后该酶表达量趋于稳定。过氧化物酶仅在基盘周边区域外胚层中表达,而在基盘中央区域(反口孔)外胚层中无表达。结论水螅基盘再生进程中过氧化物酶的表达量逐渐增加直接反映了基盘再生时细胞分化过程,基盘表达的过氧化物酶可能在维持基盘结构的稳定上起一定的作用。     

水螅营养积累对基盘组织更新进程的影响

目的观察大乳头水螅（Hydra magnipapillata ）基盘组织更新进程,探讨水螅营养积累对基盘组织更新进程的影响。方法设定水螅喂食频率梯度（代表不同的营养积累水平）,记录和观察喂食频率对水螅更新基盘组织进程的影响。通过ABTS细胞化学染色法检测水螅基盘分子标志物过氧化物酶的表达,观察水螅老基盘组织脱落后水螅体主体新生基盘组织的再生过程。结果喂食频率对水螅更新基盘组织进程有明显的影响。水螅基盘组织更新的标准过程如下;在一定的喂食频率下培养水螅,水螅体出芽区逐渐有芽体产生,随后在出芽区和基盘之间靠近芽体的位置出现缢痕,最后水螅体在缢痕处断裂为水螅体主体和老基盘组织两部分。缢痕断裂后对水螅体主体保持既定的喂食频率,其伤口能愈合但不能再生出新的基盘组织;对其降低喂食频率直至其伤口上方的芽体全部脱落后伤口处重新启动新生基盘组织的再生进程。另外,脱落的老基盘组织有两种不同的命运,即大部分老基盘组织不能发育成正常水螅体、最终解体;而小部分的老基盘组织能发育成正常的水螅体。结论水螅营养积累可能促进基盘组织更新进程,靠近断裂伤口处的芽体能抑制水螅体主体新生基盘的再生进程。     

红基盘瓢虫对橄榄星室木虱捕食作用及其模拟模型的研究

在实验室条件下研究了红基盘瓢虫对橄榄星室木虱的捕食作用。红基盘瓢虫对橄榄星室木虱的功能反应符合ＨｏｌｌｉｎｇⅡ型,而两种瓢虫（红基盘瓢虫和红星盘瓢虫）共同作用于橄榄星室木虱的功能反应符合ＨｏｌｌｉｎｇⅢ型（Ｓ型）。红基盘瓢虫对自身密度的功能反应可用Ｂｅｄｄｉｎｇｔｏｎ模型拟合;其搜索效率与个体间相互干扰的关系呈幂函数下降,可用Ｈａｓｓｅｌｌ＆Ｖａｒｌｅｙ模型模拟;搜索效率与猎物密度、自身密度间的关系为     

䗴类旋壁超微构造的研究——以麦䗴型旋壁为例*

光学显微镜下的观察表明蜓类的旋壁属于钙质微粒壳类型,对它们的电镜观察揭示的组成旋壁的晶粒的大小、形态和排列方式。对具有致密层和蜂巢层型两层式旋壁的Ｔｒｉｔｉｃｉｔｅｓ的电镜研究表明：其致密层由近等轴晶无定向排列而成;蜂巢层由短柱状晶向排列组成板状复合体,进而组合成管状孔,镶嵌在不定向排列的近等轴晶基质中构成。Ｐｓｅｕｄｏｆｕｓｕｌｉｎａ的致密层也由近等轴晶不定向排列构成,蜂巢层由粗柱晶定向排列组成     

人工饲养海葵

在腔肠动物门的教学中,过去是以水螅为实验材料。近年来由于农田环境污染,已不易采到标本,在饲养中,越冬越夏问题也常常遇到困难。我们试验用生态学原理饲养海葵,已收到了良好的效果。 1.采集海葵生活于浅海岩石上,附着在岩石上的一端称基盘,相对的一端有口,口周围有触手。采集时,用小铁锤、凿子连其所附着的小石取下放在装有备好海水玻瓶中。 2.养水取一个广口瓶(30×15厘米),放海水至24厘米处(海水中含有藻类和浮游动物),并放入海产贝类肉5克,到第15天,经发     

广西桂林底栖相D／C界线层牙形刺的新资料

桂林额头村剖面Ｄ／Ｃ界线层代表一种浅水碳酸盐台地沉积,以产底栖生物有孔虫、层孔虫、珊瑚、藻及少量腕足类和腹足类为特征。本文研究额头村剖面的微相并根据该剖面首次获得的牙形刺化石Ｐｏｌｙｇｎａｔｈｕｓｃｏｍｍｕｎｉｓｃｏｍｍｕｎｉｓ,Ｐｓｅｕｄｏｐｏｌｙｇｎａｔｈｕｓｃｏｎｔｒｏｖｅｒｓｕｓ,Ｐｓｅｕｄｏｐｏｌｙｇｎａｔｈｕｓｄｅｎ－ｔｉｌｉｎｅａｔｕｓ,Ｂｉｓｐａｔｈｏｄｕｓａｃｕｌｅａｔｕｓａｃｕｌｅａｔｕｓ,Ｂｉｓｐａｔｈｏｄｕｓｓｔａｂｉｌｉｓ,Ｓｐａｔｈｏｇｎａｔｈｕｓｓｔｒｉｇｏｓｕｓ和有孔虫、珊瑚化石的产出关系及与南边村剖面Ｄ／Ｃ界线层的对比,认为桂林浅水相Ｄ／Ｃ界线应置于８３层和８４－１层之间,Ｃｙｓｔｏｐｈｒｅｎｔｉｓ带属泥盆纪,ＣＰ间隔带属石炭系。     

哈曼马鸡卵壳的超微结构和元素成分

用扫描电子显微镜观察了中国特有鸟类哈曼马鸡（Ｃｒｏｓｓｏｐｔｉｌｏｎ ｈａｒｍａｎｉ）卵壳的超微结构,采用电感偶合等离子体光谱仪测定了卵壳中的化学元素的含量。首次报道哈曼马鸡卵壳结构与元素成分。哈曼马鸡卵壳表面晶体层、栅栏锥体层和卵壳膜层的厚度分别为９．３、３０７．１和６４．６μｍ,分别占卵壳总矿厚度的２．４％、８０．６％和１７％。在栅栏层有很多蜂窝小孔,测量了其直径。卵壳表面的蛋孔形状有圆形、椭     

白头鹞迁徒和越冬习性的初步观察

于１９９３－１９９５年每年的９月至翌年的４月,在贵州省水盘水市钟山区场坝一带进行猛禽迁徒和越冬习性的定位观察时,获得４只白头鹞Ｃｉｒｃｕｓａｅｒｕｇｉｎｏｓｕｓ标本,为贵州省冬候鸟新纪录。同时,还对白头鹞的迁徙作了初步观察。     

水蕨卵膜的形成及其超微结构的观察

蕨类植物成熟卵的周围有一层卵膜,但其细微结构和形成过程仍不清楚,本研究应用透射电镜技术对水蕨(Ceratopteris thailictroides)卵细胞发育过程中卵膜的形成及超微结构进行了观察.结果表明水蕨卵细胞在发育中期开始形成卵膜,卵上方的卵膜十分显著,是由多层嗜锇性内质网片层附着于质膜内表面形成的,成熟时卵上方的卵膜中心部分厚,向边缘逐渐变薄,在嗜锇性片层之间填充有嗜锇性物质.比较而言,卵下方及侧面的卵膜薄,由两层紧密连接的嗜锇性膜构成.首次阐明了蕨类植物卵膜形成的超微结构,并对卵膜的一些功能进行了探讨.     

黄瓜不同抗病品种与疫霉菌相互作用的超微结构研究

电镜观察发现,黄瓜（ＣｕｃｕｍｉｓｓａｔｉｖｕｓＬ．）的不同抗病品种在与疫霉菌（ＰｈｙｔｏｐｈｔｈｏｒａｍｅｌｏｎｉｓＫａｔｓｕｒａ）的相互作用过程中有不同的表现。感病性品种易被疫霉菌侵染,被侵染的叶肉组织及周围细胞中胶层解离、胞质凝聚、细胞器解体,叶片组织内有大量胞间及胞内生长菌丝。中抗病性品种也被疫霉菌侵染,但表现出胞间连丝断裂、内质网和高尔基体增多等抗病性反应,与菌丝相接触的细胞出现质膜内陷。抗病性品种出现过敏性坏死反应,叶肉细胞与入侵菌丝一同解体死亡,胞间菌丝向细胞内穿透处形成壁附加物。中抗病性品种和抗病性品种在与疫霉菌的相互作用过程中表现出不同的抗性机制。     

Histological and ultrastructural studies of the basal disk of Hydra

Summary The gastrodermis and mesoglea of the basal disk of Hydra were investigated to conclude a three-part series of papers. The gastrodermis is composed of digestive cells (most predominant cell type), mucous and nerve cells (both immature and fully differentiated). The principal function of the digestive cells appears to be storage of protein, lipid and glycogen reserves which are utilized by neighboring cells. Mucous cells apparently use some of the reserves to synthesize their secretions which lubricate cells and prevent cell damage during egestion of waste through the aboral pore. The function of the gastrodermal nerve cells is uncertain.The mesoglea of the basal disk, contains the same structural components as seen in other regions of the polyp. It is reasonable to assume that it maintains the same function of cell adhesion and migration. As the mesoglea converges on the aboral pore, it loses its structural integrity and cells are sloughed off the column.This investigation was supported by The National Science Foundation, Grant Number GB-27395.     

Expression of a novel receptor tyrosine kinase gene and a paired-like homeobox gene provides evidence of differences in patterning at the oral and aboral ends of hydra

Axial patterning of the aboral end of the hydra body column was examined using expression data from two genes. One, shin guard, is a novel receptor protein-tyrosine kinase gene expressed in the ectoderm of the peduncle, the end of the body column adjacent to the basal disk. The other gene, manacle, is a paired-like homeobox gene expressed in differentiating basal disk ectoderm. During regeneration of the aboral end, expression of manacle precedes that of shin guard. This result is consistent with a requirement for induction of peduncle tissue by basal disk tissue. Our data contrast with data on regeneration of the oral end. During oral end regeneration, markers for tissue of the tentacles, which lie below the extreme oral end (the hypostome), are detected first. Later, markers for the hypostome itself appear at the regenerating tip, with tentacle markers displaced to the region below. Additional evidence that tissue can form basal disk without passing through a stage as peduncle tissue comes from LiCl-induced formation of patches of ectopic basal disk tissue. While manacle is ectopically expressed during formation of basal disk patches, shin guard is not. The genes examined also provide new information on development of the aboral end in buds. Although adult hydra are radially symmetrical, expression of both genes in the bud's aboral end is initially asymmetrical, appearing first on the side of the bud closest to the parent's basal disk. The asymmetry can be explained by differences in positional information in the body column tissue that evaginates to form a bud. As predicted by this hypothesis, grafts reversing the orientation of evaginating body column tissue also reverse the orientation of asymmetrical gene expression.     

Histological and ultrastructural studies of the basal disk of Hydra

Summary The glandulomuscular cells of Hydra are located exclusively in the basal disk. They are derived from epithelio-muscular cells which have been forced proximally. Light and electron microscopical studies show that prior to their destruction and elimination, the transformed epithelio-muscular cells (i.e. the glandulomuscular cells) undergo certain striking morphological and physiological changes. Golgi complexes and elements of rough E. R. increase remarkably in activity, and individually or jointly produce at least six types of morphologically different droplets. One additional type of droplet is thought to originate from neighboring digestive cells. Although the chemical nature of the individual droplets is uncertain, it is known that some are Alcian blue and PAS positive and contain hyaluronic acid. These evidences suggest the presence of an acid mucopolysaccharide material, the adhesive agent which attaches the animal to a substrate. The myonemes contain thick (200 Å in diameter) and thin (60 Å in diameter) filaments as in epithelio-muscular cells. There are also filaments of intermediate sizes and large fibers (770 Å in diameter). The myonemes are oriented radially with respect to the aboral pore and therefore in addition to contributing to the contraction and relaxation of the body column, they apparently regulate the opening and closing of the aboral pore. Although there is no evidence to substantiate the mechanism for transformation of epithelio-muscular cells to glandulomuscular cells as well as cell death of the latter cell types, these problems are discussed briefly.This investigation was supported by The National Science Foundation, Grant Number GB-27395.With the technical assistance of Linda M. Bookman.     

Initial analysis of immunochemical cell surface properties, location and formation of the serotonergic apical ganglion in sea urchin embryos

In the present study it was found that serotonergic apical ganglion (SAG)-forming cells in plutei of the sea urchin, Hemicentrotus pulcherrimus, possessed a characteristic pear shape with broad apical sides and a pointed basal side in the acron epithelium. The basal side extended axons through the space between the epithelium and the basal lamina toward the midline of the embryo that aligned parallel to the embryonic anteroposterior axis. Serotonergic apical ganglion-forming cells had epithelial cell surface-specific proteins on their entire surface. The SAG in 4-arm plutei was composed of a 4-cell trunk region that aligned at right angles to the embryonic anteroposterior axis, and forked into two branches of one to two cells at both ends. Two branches extended toward the oral and the other two toward the aboral region, respectively. Double-stained immunohistochemistry using antiserotonin antibodies and oral ectoderm-specific anti-Ecto V monoclonal antibody or aboral ectoderm-specific anti-Ars antibodies indicated that SAG was in the aboral ectoderm region. Serotonergic apical ganglion cells were first detected in late gastrulae and increased in number rapidly between 36 and 48 h after fertilization, and then slowly afterwards. A 5-bromo-2-deoxyuridine incorporation study indicated that none of the increased SAG cells were in the S phase during the aforementioned period, suggesting that SAG cells do not proliferate by cell division, but acquire the property in particular cells by transdifferentiation using a mechanism that has yet to be elucidated.     

The aboral pore of hydra: evidence that the digestive tract of hydra is a tube not a sac

The digestive tract of Bilateria is a tube with a mouth at one end and an anus at the other end. Radiata, that include the phylum Cnidaria, have a blind-sac form of digestive tract with only one opening. It has therefore been commonly believed that the evolution of the body plan from Radiata to Bilateria included the change of the digestive tract from a blind sac to a tube. In this study, we report that there is a very narrow opening at the aboral end of hydra termed the aboral pore. This confirms a classical finding by Kanajew (Zool Anz, 76:37-44, 1928), but we confirmed it in both asexually reproduced and sexually reproduced polyps, demonstrating that the aboral pore represents innate morphology. We also find that the opening coincides with the site where synthesis of an extracellular matrix-degrading enzyme, hydra matrix metalloprotease, is elevated suggesting that the pore is maintained by extracellular matrix degradation. Finally, we find that there is material transfer through the opening in both inward and outward directions. From these observations, we conclude that the digestive tract and the body plan of hydra is not a blind sac as formerly believed but is a tube with a tapered end.     

A hydrophobic gate in an ion channel: the closed state of the nicotinic acetylcholine receptor

The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the 'Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic neurotransmission, and whose other members include receptors for glycine, gamma-aminobutyric acid and serotonin. Cryo-electron microscopy has yielded a three-dimensional structure of the nAChR in its closed state. However, the exact nature and location of the channel gate remains uncertain. Although the transmembrane pore is constricted close to its center, it is not completely occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A. Model calculations suggest that such a constriction may form a hydrophobic gate, preventing movement of ions through a channel. We present a detailed and quantitative simulation study of the hydrophobic gating model of the nicotinic receptor, in order to fully evaluate this hypothesis. We demonstrate that the hydrophobic constriction of the nAChR pore indeed forms a closed gate. Potential of mean force (PMF) calculations reveal that the constriction presents a barrier of height about 10 kT to the permeation of sodium ions, placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A radius hydrophobic pore can form a functional barrier to the permeation of a 1 A radius Na+ ion. Using a united-atom force field for the protein instead of an all-atom one retains the qualitative features but results in differing conductances, showing that the PMF is sensitive to the detailed molecular interactions.     

Status of the intracellular gate in the activated-not-open state of shaker K+ channels

Voltage-dependent K⁺ channels like Shaker use an intracellular gate to control ion flow through the pore. When the membrane voltage becomes more positive, these channels traverse a series of closed conformations before the final opening transition. Does the intracellular gate undergo conformational changes before channel opening? To answer this question we introduced cysteines into the intracellular end of the pore and studied their chemical modification in conditions favoring each of three distinct states, the open state, the resting closed state, and the activated-not-open state (the closed state adjacent to the open state). We used two independent ways to isolate the channels in the activated-not-open state. First, we used mutations in S4 (ILT; Smith-Maxwell, C.J., J.L. Ledwell, and R.W. Aldrich. 1998. J. Gen. Physiol. 111:421–439; Ledwell, J.L., and R.W. Aldrich. 1999. J. Gen. Physiol. 113:389–414) that separate the final opening step from earlier charge-movement steps. Second, we used the open channel blocker 4-aminopyridine (4-AP), which has been proposed to promote closure of the intracellular gate and thus specifically to stabilize the activated-not-open state of the channels. Supporting this proposed mechanism, we found that 4-AP enters channels only after opening, remaining trapped in closed channels, and that in the open state it competes with tetraethylammonium for binding. Using these tools, we found that in the activated-not-open state, a cysteine located at a position considered to form part of the gate (Shaker 478) showed higher reactivity than in either the open or the resting closed states. Additionally, we have found that in this activated state the intracellular gate continued to prevent access to the pore by molecules as small as Cd²⁺ ions. Our results suggest that the intracellular opening to the pore undergoes some rearrangements in the transition from the resting closed state to the activated-not-open state, but throughout this process the intracellular gate remains an effective barrier to the movement of potassium ions through the pore.     

The Structure of a Sessile,Stalkless Crinoid (Holopus rangii)

Specimens of Holopus rangii (order Cyrtocrinida) were collected by submersible at depths of several hundred meters in the Caribbean and fixed for light and electron microscopy. The presence of an anus is confirmed. However, the chambered organ and glandular axial organ peculiar to crinoids are lacking. The gut lumen sometimes includes partially digested prey items up to several hundred micrometers in diameter, and we propose that Holopus may feed raptorially by rapidly closing its arms over demersal zooplankton. Electron microscopy of the arm reveals a radial nerve and a radial haemal channel, which light microscopy previously failed to demonstrate. The cuticle includes bacteria that are probably symbiotic. The ten brachial nerves of the aboral nervous system unite pairwise to form five calyx nerves. The calyx nerves, one in each radial position, are connected by a pentagonal, interradial commissure and then continue to the attached end of the body where they end blindly without forming an aboral nerve center. The absence of the aboral nerve center and related internal organs strengthens the argument that no basal ossicles are included in the skeleton of the calyx and suggests that Holopus may have evolved from stalked cyrtocrinid ancestors by saltatory loss of major body parts.     

Non-junctional modulation of neurogenic twitches of the guinea-pig ileum by some peptides and other compounds in the triple bath

The effects of some neuropeptide transmitter candidates and of some other neurotoxins or drugs on conduction of neural excitation were studied in myenteric plexus-longitudinal muscle strips from the guinea-pig ileum. A preparation in a special triple bath was drawn through two rubber membranes dividing the strip into three segments. Neurogenic stimulation of the oral segment set up nerve action potentials propagating aborally across the middle segment so that the aboral segment might also be invaded. Drugs were added to the middle segment to affect neuronal propagation (non-junctional effects) which was monitored by twitch amplitude of the aboral segment. The application of bradykinin and cromakalim did not affect aboral twitches although strong contractile and relaxatory effects were observed when the drugs were applied directly to the aboral segment; no neurogenic effects thus manifested. Capsaicin and neurotensin, when applied both to the middle and aboral segments, elevated the tone of the preparations accompanied with a decrease in twitch amplitude; these effects may have been due to neurogenic stimulation and release of other motor neurotransmitters. The application of VIP, apamin and dendrotoxin to the middle as well as to the aboral segments augmented aboral twitches, which might be at least partly due to facilitation of nerve action potential propagation in nerve terminals of cholinergic motor fibres.