Structure of the Cells, Cell Division and Colony Formation in the Diatoms Isthmia enervis Ehr. and I. nervosa Ktz

The two common species of Isthmia have been studied mainly byscanning electron microscopy. The occurrence of differing cellshape in the same species is an extremely unusual feature amongstdiatoms. This is coupled with heteropolar valves. The formationof colonies and the peculiar attachment of cells to one anotheris recorded. A particularly intricate attachment of the firstgirdle band (valvocopula) to the valve is recorded. Isthmia, diatom, cell division, colony formation     

马尾松林直翅目昆虫群落的时空格局及其多样性和稳定性

在安徽省长江南岸自西向东相同地理纬度的金寺山、戴公山、九连山和麻姑山林场各选面积相等(22 m×22 m) 、林分和立地条件相似的样地2块,1998年8月～1999年7月每月下旬对乔木层、下木层(灌木草本层)、地表和落叶层、土壤层中直翅目昆虫的调查和分析表明：① 红褐斑腿蝗Catantops pinguis( Stal)是各场优势种,东亚飞蝗Locusta migratoria anilensis (Meyen)、短额负蝗Atractomorpha sinensis I. Bolivar、日本绿螽斯Holochlora japonica Brunner Wattenwyl和油葫芦Gryllus testaceus Walker为常见种;② 1周年内戴公山、金寺山、麻姑山和九连山林场的物种数、个体数和多样性指数分别是：27、159、1.28 ;26、70、1.32;35、171、1.42和 20、90、1.33;③ 下木层中含有全部调查到的种类和80 %以上的个体;④ 麻姑山林场下木层中植被复杂、盖度大,草本植物比其它林场丰富,生境也较湿润;多年来大面积施药对天敌群落损害较大,可能由于这些因素导致该场蝗虫等直翅目昆虫种类数和个体数较多、群落多样性和恢复力稳定性较强。     

The inhibition of cell division in Saccharomyces cerevisiae (Meyen) by carbon dioxide

A specific inhibiting effect of CO² on cell division in Saccharomycescerevisiae (Meyen) was shown. Two strains of S. cerevisiae weregrown in chemically-defined media in specially-designed pressurechambers equipped with sensitive pressure-measuring devices.The chambers were pressurized with 40 psi of N₂ or CO₂. Inhibitionof cell division and of production of new buds was not causedby N₂ but was caused by CO₂ when either endogenously producedor added. In contrast, metabolic production of CO₂ was unaffectedby endogenously-produced pressures which totally inhibited celldivision. Bud formation and new-cell formation (cell division) were almosttotally inhibited by 40 psi of added CO₂ when compared withaerated cultures. The DNA content per cell, however, was nearlytwice as great in the CO₂-treated cultures as in the controls.Thus inhibition of cell division in S. cerevisiae must occurby some mechanism other than by inhibition of DNA replication. (Received January 5, 1971; )     

The Development of the Fruit Walls in Carya

Both the pistillate flowers and the developing fruits of CaryaovataandC. cordiformis are covered with secretory and protectivehairs. There are two kinds of the secretory hairs. In the morefrequent one the volatile oils are accumulated under the cuticlecovering the cells of the head. In the other the secretory substancesare accumulated inside the cells. The flowers and the developingfruits of the two investigated species have quite large emergenceson which the stomata most often occur. During the developmentof the fruit lenticels are formed in the green hull. Tanninsare accumulated not only in the green hull, but also in thecarpellary layer and in the packing tissue. There are some differences between C. ovata and C. cordiformisin the course of sclerification of the green hull. In C. cordiformisthe hull is less sclerified than in C. ovata, and the sclerificationof the carpellary layer occurs later. At a certain period ratherlarge gaps are present in the lignifying shell (in the regionsof the sutures) where the cells have thin cellulose walls. Thesegaps are partly filled with sclereids. The gaps become reducedto narrow chinks, in which the cell walls remain unlignified.The hard shell is not formed in all its width at the same time.During the process of formation of the hard fruit shell theremay arise single sclereids surrounded by thin-walled cells.Within a short time these undergo a similar modification andthe tissue becomes uniform as sclerenchyma. The sclereids ofthe hard shell have, in general, strongly folded cell walls.Owing to this they overlap each other.     

东亚飞蝗中肠几丁质酶基因的克隆、序列分析及组织定位

通过RACE方法,克隆了东亚飞蝗Locusta migratoria manilensis (Meyen)几丁质酶基因 (LmChi)cDNA全序列 (GenBank 登录号：EF092841)。获得的cDNA全长1 604 bp,其中可读框1 452 bp, 编码483个氨基酸。推测其氨基酸序列与18家族昆虫几丁质酶有较高的相似性。与其他几丁质酶一样,东亚飞蝗几丁质酶序列也包含一个信号肽、一个几丁质酶活性位点、一个碳端丝氨酸富集区和一个几丁质结合域。半定量RT-PCR研究表明,LmChi基因只在东亚飞蝗不同发育阶段的中肠组织中表达,而在东亚飞蝗体壁、前肠和后肠均没有发现LmChi基因的转录。     

Mitosis, Cytokinesis and Colony Formation in Pediastrum boryanum

Uninucleate cells of Pediastrum become multinucleate by a seriesof synchronous mitoses. Mitotic nuclei are enclosed by a perinuclearenvelope of endoplasmic reticulum. Cytoplasmic cleavage of themultinucleate cells leads to the production of uninucleate,biflagellate zoospores (zooids) which are subsequently releasedinto a lenticular vesicle through a rupture in the outer layerof the parental cell wall. Within the vesicle, presumably derivedfrom part of the inner layer of parental wall, the zooids swarmactively before aggregating in a planar array. Bands of microtubulesunderlie the plasmalemma of the zooids which, when the zooidsaggregate, are usually coplanar with the newly formed colony.The role of microtubules in patterned colony formation and inthe development of the characteristic horns on peripheral cellsof colonies of Pediastrum is discussed.     

Control of palmelloid formation in the green alga Pediastrum

Pediastrum tetras, normally a non-motile colony of eight cells,aggregates into large masses of up to 1500 µ in diameterwhen grown in certain nutrient media. These masses ("palmelloids")can be prevented from forming or can be dissociated into separatecolonies by either high pH or ferric ions. The average particlesize is inversely proportional to the concentration of Fe⁺⁺⁺between zero and about 300 µM. Iron chelators such asEDDHA have no effect. These data are discussed in comparisonwith the control of palmelloid formation in other genera. (Received February 12, 1972; )     

Salt Glands in Pappophorum (Poaceae)

Salt glands were observed in two species of Pappophorum, belongingto the tribe Pappophoreae (Chloridoideae, Poaceae). Glands resemblethose described in other genera of the Gramineae; they comprisetwo cells, a large basal one and smaller upper one. Gland densityper unit surface was much higher in P. philippianum, a facultativehalophyte, than in P. pappiferum, a glycophyte. The relevanceof the recretion process for the elimination of accumulatedNa in these two species is considered. The evolutionary significanceof the presence of glands in Pappophoreae and other membersof the Chloridoideae is discussed. Salt glands, Pappophorum philippianum, P. pappiferum, Poaceae     

Genetic evidence for kin-based female social structure in common eiders (Somateria mollissima)

Kin-based social groups are commonly studied among cooperativelybreeding species but have been less studied in "nontraditional"group breeding systems. We investigated the presence of kin-basedsociality among females in the common eider (Somateria mollisima),a colonial nesting sea duck that exhibits high levels of natalphilopatry in females. Previous studies of female socialityin common eiders have been restricted to observations duringbrood rearing. However, aggregations of female common eidersare also observed during other periods of the life cycle suchas colony arrival and nesting. Here we apply a novel, empiricalframework using molecular markers and field sampling to geneticallycharacterize female social groups at several stages of the commoneider life cycle. When compared with mean estimates of interindividualrelatedness for the entire colony, significantly higher levelsof relatedness were found between females within groups arrivingto the colony in flight, between females and nearest neighborsat the time of nest site selection, and between groups of femalesdeparting the colony with ducklings. Both full-sibling and half-siblingequivalent relationships were also found within these groups.Therefore, throughout each of several stages including in-flightcolony arrival, nesting, and brood rearing, we provide the firstgenetically confirmed evidence of female kin-based social groupsin common eiders and anseriformes in general.     

Daily irradiance governs growth rate and colony formation of Phaeocystis (Prymnesiophyceae)

Phaeocystis was cultured at a range of ecologically significantdaily irradiances under nutrient-replete conditions. Below athreshold of 100 W h m^–1 day^–1, the cells were smalland flagellated, and remained solitary. Above this threshold,the cells were larger and able to form colonies. Growth rateand colony formation were maximum at sea surface irradiances(>700 W h m^–2 day^–2). Presumably, colonial growthis a strategy to maintain optimum growth rates in the watercolumn. Sinking, nutrient-stressed colonies reach low irradiancesand colonial cells can transform into small solitary flagellatedcells. These observations are important in understanding theecology and life cycle of Phaeocystis.     

Maitotoxin and P2Z/P2X7 purinergic receptor stimulation activate a common cytolytic pore

The effects ofmaitotoxin (MTX) on plasmalemma permeability are similar to thosecaused by stimulation of P2Z/P2X₇ionotropic receptors, suggesting that1) MTX directly activatesP2Z/P2X₇ receptors or2) MTX andP2Z/P2X₇ receptor stimulationactivate a common cytolytic pore. To distinguish between these twopossibilities, the effect of MTX was examined in1) THP-1 monocytic cells before andafter treatment with lipopolysaccharide and interferon-, a maneuverknown to upregulate P2Z/P2X₇receptor, 2) wild-type HEK cells andHEK cells stably expressing theP2Z/P2X₇ receptor, and3) BW5147.3 lymphoma cells, a cellline that expresses functional P2Z/P2X₇ channels that are poorlylinked to pore formation. In control THP-1 monocytes, addition of MTXproduced a biphasic increase in the cytosolic freeCa²⁺ concentration([Ca²⁺]_i);the initial increase reflects MTX-inducedCa²⁺ influx, whereas the secondphase correlates in time with the appearance of large pores and theuptake of ethidium. MTX produced comparable increases in[Ca²⁺]_iand ethidium uptake in THP-1 monocytes overexpressing theP2Z/P2X₇ receptor. In bothwild-type HEK and HEK cells stably expressing theP2Z/P2X₇ receptor, MTX-inducedincreases in[Ca²⁺]_iand ethidium uptake were virtually identical. The response of BW5147.3cells to concentrations of MTX that produced large increases in[Ca²⁺]_ihad no effect on ethidium uptake. In both THP-1 and HEK cells, MTX- andBz-ATP-induced pores activate with similar kinetics and exhibit similarsize exclusion. Last, MTX-induced pore formation, but not channelactivation, is greatly attenuated by reducing the temperature to22°C, a characteristic shared by theP2Z/P2X₇-induced pore. Together,the results demonstrate that, although MTX activates channels that aredistinct from those activated byP2Z/P2X₇ receptor stimulation, thecytolytic/oncotic pores activated by MTX- and Bz-ATP are indistinguishable.

     

Phosphorus utilization by Asterionella formosa Hass

Observations have been made on the relationship in Lake Windermerebetween the growth of Asterionella formosa and the concentrationof dissolved phosphate. Asterionellaformosa has also been grownin culture and the amount of phosphorus required by this organismhas been determined. These experiments have shown that: (1) Asterionella can take up and store in reserve phosphorusfrom concentrations below those found in phosphorus-poor lakes(i.e. below 1 µg.P/l.). (2) Growth can continue in phosphorus-deficient media by makinguse of such reserves, cell phosphorus being steadily reduced. (3) The limiting requirement per cell of phosphorus is veryminute—about 0—06µg P/10⁶ cells/1, so thatinitial concentrations as low as rog.P/l. can theoreticallyproduce a population of some i6 x io6 cells/l. before limitationby phosphorus deficiency. This has been realized in culture.The behaviour of Asterionella formosa growing in nature hasbeen found to conform with that found in culture. It is concludedfrom such observations that phosphorus deficiency is unlikelyto provide a limit to growth of Asterionella in Windermere,despite the very low initial concentration of dissolved phosphate.Further experiments have shown that Asterionella cells low inphosphorus can rapidly take up added phosphate from lake waterbut not from distilled water. Some factors which affect therate of phosphate uptake of depleted cells are investigated,and attempts have ben made to throw some light on the natureof the apparent difference between lake water on the one handand distilled water and a number of artificial lake waters onthe other. No conclusion is reached on the reason why Asterionellacells behave differently in lake water and in artificial media.     

Phosphorylation of myo-inositol in ripening grains of rice and wheat. Incorporationof phosphate-32P and myo-inositol-3H into myo-inositol phosphates

To elucidate the mechanism of the phosphorylation of myo-inositolin the process of phytate formation, feeding experiments oforthophosphate-³²P and myo-inositol-³H in the ripening grainsof rice and wheat were performed. It was found that ³²P and³H were incorporated into myo-inositol mono- and hexa-phosphates.The same results were obtained when a mixture of "cold" myo-inositolpolyphosphates was administered to the grains before feedingphosphate-³²P. Based on these results it is concluded that phosphorylationof free myo-myo-inositol in the formation of phytate does nottake place in a stepwise fashion but may proceed through anunknown myo-inositol derivative. (Received August 2, 1967; )     

Environmental factors controlling colony formation in blooms of the cyanobacteria Microcystis spp. in Lake Taihu,China

Nitrogen (N) and phosphorus (P) over-enrichment has accelerated eutrophication and promoted cyanobacterial blooms worldwide. The colonial bloom-forming cyanobacterial genus Microcystis is covered by sheaths which can protect cells from zooplankton grazing, viral or bacterial attack and other potential negative environmental factors. This provides a competitive advantage over other phytoplankton species. However, the mechanism of Microcystis colony formation is not clear. Here we report the influence of N, P and pH on Microcystis growth and colony formation in field simulation experiments in Lake Taihu (China). N addition to lake water maintained Microcystis colony size, promoted growth of total phytoplankton, and increased Microcystis proportion as part of total phytoplankton biomass. Increases in P did not promote growth but led to smaller colonies, and had no significant impact on the proportion of Microcystis in the community. N and P addition together promoted phytoplankton growth much more than only adding N. TN and TP concentrations lower than about TN 7.75–13.95 mg L⁻¹ and TP 0.41–0.74 mg L⁻¹ mainly promoted the growth of large Microcystis colonies, but higher concentrations than this promoted the formation of single cells. There was a strong inverse relationship between pH and colony size in the N&P treatments suggesting CO₂ limitation may have induced colonies to become smaller. It appears that Microcystis colony formation is an adaptation to provide the organisms adverse conditions such as nutrient deficiencies or CO₂ limitation induced by increased pH level associated with rapidly proliferating blooms.     

Phytoplankton aggregate formation: observations of patterns and mechanisms of cell sticking and the significance of exopolymeric material

Flocculation of ‘sticky’ phytoplankton cells intorapidly sinking aggregates has been invoked as a mechanism explainingmass sedimentation of phytoplankton blooms in the ocean. Phytoplanktonstickiness, defined as the probability of adhesion upon collision,is one key factor determining the potential for aggregate formation.In the laboratory, we examined variation in stickiness in fivespecies of diatoms and two species of flagellates grown in batchcultures. We also investigated the production of paniculatemucus by phytoplankton cells and its role in aggregate formation,and we studied the effects of solute exudates on cell stickiness.Four of the five diatoms investigated were significantly sticky,while one diatom and both of the flagellates were not sticky.Stickiness varied considerably within species. In the diatomSkeletonema costatum, the typical but not entirely consistentpattern was that stickiness decreased with age of the batchcultures. We were otherwise unable to establish consistent relationshipsbetween cell stickiness and the growth stage of the algae, environmentalconcentrations of inorganic nutrients, and abundances of suspendedand epiphytic bacteria. We showed that the diatom S.costatumat times excretes a solute substance that depresses flocculation.This may reduce cell losses from the euphotic zone during thegrowth phase due to flocculation and sedimentation. We demonstratedtwo different mechanisms of phytoplankton aggregate formation.In the diatom S.costatum, the cells are sticky in themselves,and coagulation depends on cell-cell sticking and does not involvemucus. Aggregates are composed solely of cells. Cells of thediatom Chaetoceros affinis, on the other hand, are not in themselvessticky. Transparent exopolymeric particles (TEP), produced bythe diatom, cause the cells to aggregate and coagulation dependson TEP-cell rather than cell-cell sticking. Aggregates are formedof a mixture of mucus and cells. We found several species ofdiatoms and one flagellate species to produce copious amountsof TEP. TEP from some species (e.g. Coscinodiscus sp.) is stickyand may cause other, non-sticky particles to coagulate. Thisemphasizes the potential importance of diatom-derived paniculatemucus for particle flocculation in the ocean.     

Structure and Histochemistry of Stomata and Epidermal Cells in Five Species of Polypodiaceae

The epidermal structure of the five species of ferns, Arthromeriswallichiana (Spr.) Ching., Drymoglossum piloselloides (Prest.),Drynaria quercifolia (L.) J. Smith, Lepisorus nudus (Hook.)Ching. and Pyrrosia nuda (Gies.) Ching., has been investigated.Fifteen types of stomatal structures have been identified ofwhich copolo-desmocytic and coperi-desmocytic are new types.Four more possible stomatal structures: ccpolo-peri-, codesmo-polo-,codesmo-peri- and duplodesmocytic, are suggested. Localizationof starch, insoluble polysaccharides, protein and lipids hasbeen examined histochemically in the guard cells, subsidiarycells and epidermal cells. In Drynaria starch plastids and plastidscontaining both starch and protein are present in guard cells.Starch plastids are present in the subsidiary cells of all speciesexcept in Arthromeris, whereas, they are present in epidermalcells of only Drymoglossum and Lepisorus. Granular or amorphousinsoluble polysaccharides (other than starch) are present inguard cells of all the species, in the subsidiary cells of Arthromeris,Drynaria and Pyrrosia, and in the epidermal cells of Pyrrosia.Except in Pyrrosia lipids are present in the guard cells. Subsidiarycells of Drynaria and the epidermal cells of Arthromeris andDrynaria show lipid bodies. The presence of plasmodesmata andectodesmata is demonstrated in the epidermal cells of Drymoglossum.     

Phosphatic Shell Formation in Atremate Brachiopods

The atremate brachiopods are unique in that they possess shellsof calcium phosphate. In Lingula adamsi and Gloltidia pyramidata,the shell mineral is (CO₃ + F)-containing apatite and is crystallo-chemicallysimilar but not identical to the mineral francolite. The shellof Glottidia consists of a thin periostracum, a mineralizedthick primary layer, and alternating mineralized layers andless mineralized chitin layers. The basic unit of the crystalsis the spherulite. Proteinaceous and glycosaminoglycan (GAG)matrices are present in the primary and mineralized layers.The GAGS in the chitin layer are morphologically different fromthose of the other layers. The GAGS are intimately associatedwith the apatite crystals. Shell formation appears to be mediated by three different typesof cells in the outer epithelium. The cells primarily involvedin the mineral formation are characterized by many vacuoleswith electron-dense granular inclusions containing Ca, P, andS. The connective tissue at the anterior edge of the mantlealso contains fine granules with Ca, P, and S. Those granulesare considered to be a mineral reserve for shell formation.Some problems of the mechanisms of shell formation are discussed.