On the nature of bristles in Scenedesmus

Summary The existence of bristles, the hair-like appendages in several species of the genus Scenedesmus has been confirmed.The ultrastructure of bristles in Scenedesmus helveticus Arlet, Sc. acutus Meyen and Sc. acuminatus/Lagerh./Chodat has been studied by negative staining. While bristles of Sc. helveticus are composed of several microstrands with a regular pattern of cross-striation, the bristles of spineless species Sc. aculus and Sc. acuminatus seem to be composed only of individual microstrands.These investigations of bristles suggest their protein composition.     

La paroi cellulaire de Coelastrum (Chlorophycées)

The cell wall of Coelastrum is usually composed of three layers. The outermost layer was studied most extensively. It consists of erect tubules which often bear long bristles whose function may be to stabilize the algae in its environment. The cell wall can modify its morphology according to the environment.     

Obervations on the occurrence of scales and bristles of mallomonas spp. (Chrysophyceae) in the micro-laminated sediments of a small lake in finnish North Karelia

Scales and bristles ofMallomonas crassisquama (Asmund) Fott andM. elongata Reverdin are reported from the laminated sediments of Laukunlampi, a small kettlehole lake in N. Karelia, Finland. The white summer laminae in the deeper sediment are composed almost entirely ofM. crassisquama scales and bristles. The taxonomy, ecology and distribution ofM. crassisquama andM. elongata are briefly discussed and factors influencing the preservation of scales and bristles in sediments are considered. It is suggested that analysis of sedimentary associations of scales, bristles and cysts could be used to improve cyst taxonomy inMallomonas.     

Entwicklungsgeschichtliche Untersuchungen an zentrischen Diatomeen

The marine diatomChaetoceros didymum Ehrenberg has been studied with respect to cell morphology, fine structure of the frustule, and life history. Additional observations were made on otherChaetoceros species grown in culture. Co-existence of linear colonies with both intercellular spaces (foramina) and long stiff bristles is mediated by two morphogenetic peculiarities. After cell division the bristles grow out from the apices of the new valves and pass through preformed “bristle openings”, two of which occur in each girdle. They cross each other and fuse inseparably, thus bridging the foramina bilaterally. The irreversibility of cell junctions established in this manner results in two types of special “colony-separation-divisions”: (1) An equal, but heterovalvate division forming a pair of early dehiscing colony-end-valves; (2) a rare acytokinetic and unequal division. In resting spore formation a heterovalvate division gives rise to a pair of specialized spore-mother-cell hypothecae. Two consecutive acytokineses inside either mother cell follow, the first of which produces the spore epivalvae, the second the spore hypovalvae. In spore germination usually two consecutive acytokineses exchange the specialized valves of the spore by colony-end-valves, thus giving rise to a one-celled colony.C. didymum is monoecious, though most of the sexualized colonies are either completely male or contain vegetative and female cells. The protoplast of the spermatogonangium is usually divided into 8 naked spermatogonia by 3 steps of diploid mitoses, the first of which may or may not be followed by deposition of a pair of rudimentary valves. The spermatocytes undergo a swelling phase, which forces the parental frustule open; thereafter, 2 steps of meiotic nuclear and cell divisions follow; these form 4 uniflagellate and, normally, monoplastidic male gametes (spermia). InC. eibenii with non-dehiscent parental frustules, the spermia are released via bristle openings. The oogonia contain one functioning and two pycnotic nuclei as a result of meiosis. The spermia, however, may have entered the oogonium via bristle openings, possibly already at zygotene, though nuclear fusion is delayed until the egg has become mature. Thereafter, the zygote leaves the oogonial frustule through one of the bristle openings to which it still remains attached. In its isometric phase the zygote is surrounded by the fertilisation membrane. Its later anisometric growth is supported and probably directed by a system of silica rings, the preperizonium, which, in contrast to the otherwise comparable perizonium of pennate diatoms, forms a common layer with the surrounding scale-bearing fertilisation membrane. Finally, two consecutive acytokinetic (metagamic) mitoses induce the deposition of the two valves of the “Erstlingszelle” inside the auxospore envelope, which is ruptured during these last events and thus liberates the new enlarged cell.     

Ultrastructure of the male nephridium and its role in spermatophore formation in spionid polychaetes (Annelida)

Summary The mature male nephridia ofPolydora ligni andP. websteri (Polychaeta: Spionidae) are segmental organs composed of a ciliated nephrostome connected to a nephridial canal that crosses the intersegmental septum, expands into a large modified part extending dorsally through the coelom and subsequently narrows into a canal terminating in a dorsal nephridiopore. The nephridial canal is ciliated throughout and is composed of several cell types. Cells in the expanded region of the nephridia of both species contain large urn-shaped depressions filled with long microvilli. InP. ligni, one section of a nephridium contains cells packed with electron-dense granules that are not observed inP. websteri.The spermatophores ofPolydora ligni are composed of a central sperm mass surrounded by a layer of randomly oriented tubules that form a capsule around the sperm and taper into a long thin tail. These tubules are identical in dimensions to the microvilli present in parts of a nephridium and apparently are derived from these microvilli. The spermatophore capsule ofP. websteri is composed of similar tubules also presumed to originate from nephridial microvilli.The microvilli in nephridia of both species are surrounded with a glycocalyx that may function as an adhesive to hold the spermatophore capsule together. This glycocalyx may also function as a species specific message when encountered by a receptive female.Contribution Number 179 from Harbor Branch Foundation, Inc.     

Utilization of organic substrates during mixotrophic and heterotrophic cultivation of algae

Pure cultures ofChlorella pyrenoidosa (82) andScenedesmus obliquus (125) were grown in the nutrient medium according to Benson in the presence of 0·05m sugars or 0·025m sodium salts of organic acids. The density of culture was measured throughout the course of growth. Satisfactory heterotrophic sources of nutrition forChlorella pyrenoidosa appear to be galactose, glucose and acetate, whereasScenedesmus utilizes glucose, cellobiose and acetate. The growth ofChlorella in the light is enhanced by galactose, glucose, fructose, cellobiose and maltose, that ofScenedesmus by glucose, fructose, cellobiose, galactose, maltose, acetate and pyruvate. Soluble starch suppresses growth of both cultures. The role of the substrates is discussed. It follows from the results that the growth-promoting sugars and organic acids can act not only as a source of carbon during general carbon shortage but also as ergastic material. The mechanism of utilization of some organic substrates will be taken up in a subsequent paper.     

A STUDY OF WALL ORNAMENTATION IN CULTURES OF SCENEDESMUS

In a comparative study, six strains of Scenedesmus isolated from one small pond were examined in culture. Three of the isolates, S. denticulatus, S. dispar, and S. abundans, proved to be morphologically quite stable when studied in the laboratory. In an axenic culture of any one of the three pleomorphic strains one could find coenobia which resemble S. longispina or S. armatus. High percentages of four-celled coenobia with several ridges but with only two spines (the S. semipulcher type) were found typically in older cultures of two of the pleomorphic cultures. Long, delicate appendages (bristles) were easily detected on most coenobia in desiccated preparations of all but the S. dispar culture. The use of cultures in identifying Scenedesmus coenobia is discussed.     

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

Microalgal lipids are promising alternative feedstocks for biodiesel production. Scenedesmus sp. NJ-1, an oil-rich freshwater microalga isolated from Antarctica, was identified to be a suitable candidate to produce biodiesel in this study. This strain could grow at temperatures ranging from 4 to 35?°C. With regular decrease in nitrate concentration in the medium, large quantities of triacylglycerols accumulated under batch culture conditions detected by thin layer chromatography and BODIPY 505/515 fluorescent staining. Scenedesmus sp. NJ-1 achieved the average biomass productivity of 0.105?g?l^?1?d^?1 (dry weight) and nearly the highest lipid content (35?% of dry cell weight) was reached at day 28 in the batch culture. Neutral lipids accounted for 78?% of total lipids, and C18:1 (n-9), C16:0 were the major fatty acids in total lipids, composing 37 and 20?% of total fatty acids of Scenedesmus sp. NJ-1 grown for 36?days, respectively. These results suggested that Scenedesmus sp. NJ-1 was a good source of microalgal oils for biodiesel production.     

STRUCTURE AND FUNCTION OF THE BRISTLES OF PEDIASTRUM BORYANUM (CHLOROPHYTA)1

Tufts of long delicate bristles were detected on mature colonies of Pediastrum boryanum (Turp.) Meneghini. The bristles are not uniform in length and can exceed 100 μm. Bristle number per tuft can exceed eighty. Ultrastructure studies revealed that tufts are an aggregate of hexagonal tubules arranged in staggered rows. Each hexagonal tubule has an inner diameter of 6 nm and is made up of six interconnected subunits 4 nm in diameter that are shared by adjoining tubules. The bristles can be easily removed from mature colonies with a vortex stirrer. Removal of bristles from mature colonies in culture results in the loss of buoyancy and subsequent settling to the bottom of the flask.     

Strukturveränderungen am PlasmalemmaAphelidium-infizierter Scenedesmus-Zellen

Zusammenfassung Es werden Strukturveränderungen am Plasmalemma vonScenedesmus acutus-Zellen beschrieben, die vonAphelidium spec. infiziert waren. Der Parasit entwickelt imScenedesmus-Cytoplasma ein Plasmodium, dessen Plasmalemma von dem durch den Parasiten eingestülpten Teil desScenedesmus-Plasmalemmas umgeben ist. Beide Membranen verlaufen mit geringem Abstand parallel und bilden manchmal eine compound membrane. Der verlagerte Teil desScenedesmus-Plasmalemmas hat eine mehr oder weniger deutlich asymmetrische Struktur, während der nicht verlagerte Teil (an der Zellwand) symmetrisch ist. Das Bild dieser Membranen ist von der Fixierung abhängig. Reste des nichtverlagerten Teils desScenedesmus-Plasmalemmas kommen sogar dann noch vor, wenn das Cytoplasma völlig aufgelöst ist; sie treten in Form Lamellen-ähnlicher, trilaminarer, symmetrischer Strukturen auf. Gelegentlich fusionieren die Plasmalemmen des Wirtes und des Parasiten artifiziell miteinander und bilden Vesikel. Unterschiede zwischen dieser parasitischen Assoziation und der vonSc. armatus mit einem anderen Typ vonAphelidium (Schnepf et al. 1971) werden erwähnt.

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Structural modifications in the plasmalemma ofAphelidium-infectedScenedesmus cells

Summary Modifications in the structure of the plasmalemma of cells ofScenedesmus acutus on infection by a strain ofAphelidium are described. The parasite develops a plasmodium inside theScenedesmus cytoplasm, its plasmalemma is surrounded by a dislocated portion of theScenedesmus plasmalemma. Both membranes run parallel, a short distance apart, and occasionally form a compound membrane. The dislocated portion of theScenedesmus plasmalemma has a more or less asymmetrical structure whereas the undislocated portion (at the cell wall) is nearly symmetrical. The appearance of these modifications is dependent on the fixation method. Remnants of the undislocated part of theScenedesmus plasmalemma are found even when the host cytoplasm has lysed completely; they occur in the form of lamella-like, trilaminar symmetrical structures. Occasionally the plasmalemma of the host and of the parasite fuse artificially to form vesicles. Differences between this parasitic association and that ofSc. armatus with another strain ofAphelidium (Schnepf et al. 1971) are described.

     

The capability of the algaeChlorella vulgaris andScenedesmus obliquus of utilizing amino acids as the sole nitrogen source

The capability of utilizing 20 amino acids and 2 amides as the sole nitrogen source for growth was studied in two green algae (Chlorophyceae). A comparison was made of the growth rate of algae in a mineral nutrient solution containing nitrate as the nitrogen source, with that in the same solution in which nitrogen in the form of nitrate was substituted by an equivalent nitrogen amount in the form of various amino acids. In addition to this, another series of experiments was carried out in whioh both culture media were supplied with glucose. The results show that both algae utilize a series of amino acids in dependence of their structure (mostly 3-carbon amino acids). The growth rate ofChlorella in the presence of these sources is the same as in nitrate, that ofScenedesmus even much higher. In the cultures containing glucose both algal species exhibit a higher growth rate in the media with the nitrate nitrogen source than in those with amino acids (with the exception of glycine inScenedesmus).     

Bristle patterns,clones and cell competition along the anterior margin ofNotch wings ofDrosophila hydei

Summary The bristle pattern along the anterior margin ofNotch (N1-22.3) wings ofDrosophila hydei and the occurrence ofyellow (y 1–38.8) marked clones induced by X-ray irradiation during various larval stages are described. UnirradiatedN/N ⁺ wings show gaps (notches) in the longitudinal bristle rows along the 1st longitudinal vein, with tufts of bristles particularly near gaps. X-ray irradiation increases the number and total length of the gaps. The patterning of bristles along the margin depends on theN ⁽⁺⁾ genotype of the induced clones. RecombinantN ⁺/N ⁺ clones from irradiated wings show excessive growth with an autonomous wildtype bristle pattern. Characteristically, these clones do not respect the dorso-ventral compartment boundary along the wing margin, do not follow an exponential (2ⁿ) growth pattern, tend to fill the gaps with bristles and theiryellow medial row bristles are less often interspersed withy ⁺ bristles than described forN ⁺/N ⁺ wings. HomozygousN appears to be a cell lethal condition inD. hydei as it is inD. melanogaster. When y clones were kept phenotypicallyNotch (viz.,N/N/N ⁺) as the background cells, we found a lower number ofy bristles, a lower percentage of mosaic wings but also a reltive deficiency ofy ⁺ interspersions. The latter is discussed in relation to a possible clonal originof the notches.     

Influence of <Emphasis Type="Italic">Daphnia</Emphasis> infochemicals on functional traits of <Emphasis Type="Italic">Microcystis</Emphasis> strains (Cyanobacteria)

We conducted a laboratory experiment to investigate the influence of Daphnia infochemicals on growth rate, microcystin production, colony formation and cell size of eight Microcystis strains isolated from two lakes. The strains were characterized genetically by their 16S-23S rDNA ITS sequence. The experiment was composed of four treatments: (1) a control using filtered WC medium, (2) addition of Scenedesmus obliquus culture medium filtrate, (3) addition of Daphnia magna culture medium filtrate and (4) addition of sodium octyl sulphate, a commercially available Daphnia infochemical. Our results showed that sympatric strains differed strongly for the measured functional traits, while no correlations between traits were found. Between-strain differences in growth rate, microcystin production, colony formation and cell size were generally larger than the differences in phenotypes observed between treatments. Despite this, several strains reacted to the infochemicals by changing functional trait values. Daphnia culture medium filtrate and, to a lesser extent, sodium octyl sulphate had a negative influence on the growth rate of half of the strains and stimulated microcystin production in one strain, but the latter effect was not Daphnia-specific as Scenedesmus culture medium filtrate had the same effect. Daphnia culture medium filtrate also induced colony formation in one strain. Our data suggest that Daphnia infochemicals generally have a weak influence on growth rate, microcystin production and colony formation of Microcystis strains as compared to the inter-strain variability, while existing inducible effects are highly strain-specific.     

微藻光密度与细胞密度及生物质的关系

以四种常见微藻,小球藻(Chlorella sp.XQ-20044)、栅藻(Scenedesmus sp.SS-200716)、绿球藻(Chlorococcum sp.)和螺旋藻(Spirulina sp.CH-164)为实验材料,用梯度稀释法测定对数生长期不同浓度藻液的光密度(OD)、细胞密度和生物质干重(DW),在光自养分批培养模式下对4种微藻进行OD-波长(350—800 nm)扫描,同时测定细胞密度和生物质干重,分析藻液OD与细胞密度、生物质干重的关系。结果表明:在任何波长下,对数生长期的4种微藻细胞密度与OD值、生物质干重与OD值的变化都不成比例,波长不同其拟合曲线偏离直线的程度不同。但是,在435 nm处这种关系最接近直线,可以用直线方程近似描述(R20.98),其它波长处细胞密度-OD、干重-OD的关系都可以用二项式方程很好地描述(R20.99)。因此,光密度法适用于连续和半连续培养,可以用435 nm处测得的OD值计算细胞密度与干重。但是在分批培养模式下,4种微藻DW/OD比值随着培养时间均逐渐上升。小球藻DW/OD540为0.19—0.44 g/L,栅藻DW/OD540为0.36—0.53 g/L,绿球藻DW/OD540为0.48—0.75 g/L,螺旋藻DW/OD560为0.46—0.74 g/L,因此分批培养模式下采用测定藻液OD值反映细胞密度和生物质的方法不适用,只有直接测定细胞密度和生物质才是准确的。研究结果为正确使用分光光度法监测微藻生长提供依据。     

Morphology of antennal sensilla of the brown spruce longhorn beetle,Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae)

The antennal sensilla of the brown spruce longhorn beetle, Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae) were examined with particular focus on the sensilla present on the apical flagellomere. T. fuscum antennae are composed of 11 segments, namely the scape, pedicel, and nine flagellomeres. Nine types of sensilla were observed: three types of sensilla chaetica, sensilla trichodea, two types of sensilla basiconica, grooved peg sensilla, thick-walled sensilla, and Böhm bristles. Seven of these types were present on the apical flagellomere, the exceptions were sensilla chaetica type 3 and Böhm bristles. There were no significant differences in the distribution or density of sensilla present on the ninth flagellomere of males and females, except that males had significantly more sensilla chaetica type 1, which are put forward as the putative contact chemoreceptors for T. fuscum.     

MICROTUBULE ARMS AND CYTOPLASMIC STREAMING AND MICROTUBULE BENDING AND STRETCHING OF INTERTUBULE LINKS IN THE FEEDING TENTACLE OF THE SUCTORIAN CILIATE TOKOPHRYA

Microtubules attached to the pellicle at the tips of tentacles pivot through about 140° on these attachments, splay apart, and bend along their longitudinal axes when feeding occurs. The tubules could be bending in response to pellicular contractions; active bending, sliding, or contraction of the tubules may not be involved. Intertubule links apparently prevent tubules from splaying apart at certain levels. These links are probably under tension during feeding. They stretch; they sometimes become half as thick and eight times as long as they are before feeding. Often, tubules joined together by these links also change in shape; they become slightly flattened and elliptical in cross section. Cytoplasm from the ciliate Tetrahymena is drawn down a feeding tentacle inside an invagination of the Tokophrya cell membrane from the tentacle tip. The positions of arm-bearing microtubules around such invaginations indicate that arms are involved in moving invaginations along. The edges of the perforated Tetrahymena cell membrane are "sealed" to the cell membrane of Tokophrya around each feeding tentacle tip.     

Drosophila microRNAs 263a/b Confer Robustness during Development by Protecting Nascent Sense Organs from Apoptosis

miR-263a/b are members of a conserved family of microRNAs that are expressed in peripheral sense organs across the animal kingdom. Here we present evidence that miR-263a and miR-263b play a role in protecting Drosophila mechanosensory bristles from apoptosis by down-regulating the pro-apoptotic gene head involution defective. Both microRNAs are expressed in the bristle progenitors, and despite a difference in their seed sequence, they share this key common target. In miR-263a and miR-263b deletion mutants, loss of bristles appears to be sporadic, suggesting that the role of the microRNAs may be to ensure robustness of the patterning process by promoting survival of these functionally specified cells. In the context of the retina, this mechanism ensures that the interommatidial bristles are protected during the developmentally programmed wave of cell death that prunes excess cells in order to refine the pattern of the pupal retina.     

Restoration of wing margins in Lyra mutants of Drosophila melanogaster

Lyra is a dominant, homozygous lethal mutation of Drosophila melanogaster; in heterozygotes the wings lack portions of the anterior and posterior margins including the characteristic bristles. We have found that, in addition to the loss of bristle forming cells, there is a decrease in the number of wing surface cells that varies between 10 and 20%. However, we observed no histological evidence of excessive cell death in either the larval discs or the pupal wing precursors in Lyra flies. Restoration of all or part of the normal wing margins occurs in some, but not all, cases of morphogenetic mosaics, in which there were patches of wild-type cells in Lyra wing margins due to irradiation-induced mitotic recombination. Analysis of these restorations, using margin bristles as indicators, shows that the Lyra wild-type gene is not involved in bristle formation per se and further that its expression is not cell autonomous. Instead the effect of the Lyra mutation appears to be associated with development of a margin forming subpopulation of cells and to influence the characteristic pattern of cells and bristles in the wing margin via an inductive interaction. The dorsal-ventral boundary can be demonstrated in the de facto wing margins of Lyra mutants suggesting that its origin is independent of any function Lyra might have in normal wing margin morphogenesis. In wing margin restorations the dorsal-ventral boundary is clearly delimited by trichomes and somewhat less rigorously shown by the margin bristles. Further, in these restorations ventral clones induce dorsal bristles, as well as ventral ones, and vice versa, indicating that the influence of Lyra is not restricted by the dorsal-ventral boundary.     

SECRETION AND DEPLOYMENT OF BRISTLES IN MALLOMONAS SPLENDENS (SYNUROPHYCEAE)1

Mallomonas splendens (G. S. West) Playfair has a cell covering of siliceous scales and bristles. Interphase cells bear four anterior and four posterior bristles that each articulate, at their flexed basal ends via a complex of labile fibers (the fibrillar complex), on a specialized body scale (a base-plate scale). Body scales, base-plate scales and bristles are formed independently of each other and at different times in silica deposition vesicles (SDVs) that are associated with one of the two chloroplasts. The fine structure of scale and bristle morphogenesis in M. splendens agrees with that previously described for Synura and Mallomonas. Four new posterior bristles are formed at late interphase with their basal ends towards the cell posterior. The fibrillar complex is formed in situ on the bristle in the SDV. Mature bristles are secreted one by one onto the surface of the protoplast, beneath the layer of body scales, where the basal ends of the bristles adhere to the plasma membrane via the fibrillar complex. The extrusion of posterior bristles and their deployment onto the cell surface was monitored with video. A fine cellular protuberance accompanies the bristles as they are extruded from beneath the scale layer with their basal ends leading. When distant from the cell, the basal ends of the bristles appear attached to the protuberance, possibly by way of their fibrillar complexes. Once bristles are fully extruded, and their tips free in the surrounding environment, the bristle bases are drawn back to the posterior apex of the cell, apparently by the now shortening protuberance. Thus a 180° reorientation of the posterior bristles has been effected outside the cell. Thin-sections of cells that are extruding bristles show a threadlike, cytoplasmic extension of the cell posterior which may be analogous to the protuberance seen in live cells. Four new posterior base-plate scales are secreted after the bristles have reoriented. Scanning electron microscopy indicates that the fibrillar complex is involved in positioning the bristles onto their respective base-plate scales. Anterior bristles are formed in new daughter cells in the same orientation as the posterior bristles; thus they are extruded tip first and no reorientation is required.     

Elektronenmikroskopische Untersuchung alternder Zellen von Pseudomonas rhodos

During a 10 day-incubation on agar surfaces at 30°C, cells of the gram-negative soil bacterium Pseudomonas rhodos pass through three phases distinguishable by physiological and morphological criteria. When viewed by electron microscopy, typically “rolled” mesosomes could frequently be observed in young cells. In aged cells instead, loosely rolled or stretched-out, flattened tubules could be discerned, presumed to be degenerate mesosomes. Tubular flattened structures have been isolated from these cells by lysozyme treatment or sonication and were concentrated by differential centrifugation. Electron micrographs of these preparations showed long, straight tubules which sometimes appeared sealed at one end. Their width was 34±5 nm. They contained a lining of material, which could be digested by trypsin leaving behind an electron-transparent matrix. In rare cases, isolated tubules showed a periodic fine structure composed of ellipsoidal subunits. Optical diffraction analysis yielded a lattice consisting of subunits arranged in helices of pitch-angle 27°; the unit cell dimensions were shown to be 112×56 Å. Owing to their sensitivity to trypsin, components of the regular lattice are supposed to consist of protein. It is postulated that these protein components are layered onto a tubular membrane. These tubules are clearly distinguishable by their shape and fine structure from the periodic structure of a P. rhodos cell wall layer, which exhibits a tetragonal pattern, and also from polyheads and polysheaths of defective bacteriophages. Their possible origin from intact mesosomes is discussed.