Multiple aminoacyl-tRNA synthetases (translases) in temperature acclimation of eurythermal fish

The temperature dependency of activity of the entire set of aminoacyl-tRNA synthetases (protein synthetic translases) has been studied in the laboratory rat and in toadfish (Opsanus tau) acclimated to 20 δC or to 10 δC. The complex temperature responses of these enzyme systems reveal the presence of multiple forms for the translases of most amino acids and show adaptive behavior of these systems with respect to body temperature of the animal. The phenylalanine translase system has been studied in detail, and adaptation of this system at low temperatures correlates with adaptation in the elongation factor system. All known protein synthetic components appear to be coordinated in adaptive responses with the exception of ribosomes. Our data indicate no rôle for ribosomes in adaptation of the protein synthetic system and apparently no rôle for ribosomes in protein synthesis at all in rat and fish. This finding may solve some long-standing paradoxes in the protein synthesis field concerning the mechanism by which ribosomes participate in protein synthesis.     

Composés bromés de Rytiphlea tinctoria (Rhodophyceae)

Four aromatic bromo compounds have been isolated from the ethanolic extract of Rytiphlea tinctoria after treatment with diazomethane: 2,4-dibromo-1,3,5-trimethoxy-benzene,5,6,3′,5′-tetrabromo-3,4,2′,4′,6′-pentamethoxydiphenylmethane, 5,6-dibromo-3,4-dimethoxy-benzyl alcohol and its ethyl ether. In addition to sterols, amino acids, this extract also contains quinonoid bromo-pigments which could play a rôle in photosensitisation of chlorophylls, a rôle normally taken by the phycobilins, in other Rhodophyceae.     

The Dynamics of Turing Patterns for Morphogen-Regulated Growing Domains with Cellular Response Delays

Since its conception in 1952, the Turing paradigm for pattern formation has been the subject of numerous theoretical investigations. Experimentally, this mechanism was first demonstrated in chemical reactions over 20 years ago and, more recently, several examples of biological self-organisation have also been implicated as Turing systems. One criticism of the Turing model is its lack of robustness, not only with respect to fluctuations in the initial conditions, but also with respect to the inclusion of delays in critical feedback processes such as gene expression. In this work we investigate the possibilities for Turing patterns on growing domains where the morphogens additionally regulate domain growth, incorporating delays in the feedback between signalling and domain growth, as well as gene expression. We present results for the proto-typical Schnakenberg and Gierer–Meinhardt systems: exploring the dynamics of these systems suggests a reconsideration of the basic Turing mechanism for pattern formation on morphogen-regulated growing domains as well as highlighting when feedback delays on domain growth are important for pattern formation.     

Effects of electrocoagulation of cerebral neurosecretory cells and implantation of corpora allata on oöcyte development in Locusta migratoria

The implantation of active corpora allata into intact Locusta females during growth accelerates pre-vitellogenic oöcyte growth and vitellogenesis. Localised stimulation of yolk deposition follows the implantation of active corpora allata between the ovarioles demonstrating a gonadotrophic rôle for the corpus allatum hormone. Electrocoagulation of the median neurosecretory cells of the brain prevents vitellogenesis whilst pre-vitellogenic oöcyte growth occurs normally. Implantation of active corpora allata into females with ablated cerebral neurosecretory cells promotes vitellogenesis in a proportion of test animals although mature oöcytes are never produced.It is suggested that the rôle of the median neurosecretory cells during egg development in Locusta is primarily concerned with the activation and maintenance of activity of the corpora allata. The corpus allatum hormone acts both metabolically and gonadotrophically.     

Implications of the Precautionary Principle: Is it a Threat to Science?

Scientific research is of proven value to protecting public health and the environment from current and future problems. We explore the extent to which the Precautionary Principle is a threat to this rôle for science and technology. Not surprisingly for a relatively simple yet still incompletely defined concept, supporters of the Precautionary Principle come from different viewpoints, including a viewpoint that is at least uneasy with the rôle of science, and particularly its use in risk assessment. There are also aspects of the Precautionary Principle that inherently restrict obtaining and using science. The Hazardous Air Pollutant (HAP) provisions in the US Clean Air Act Amendments are an example of the Precautionary Principle, which both shifted the burden of proof so that the onus is now on showing a listed compound is harmless, and required maximum available control technology (MACT) instead of a primarily risk-based approach to pollution control. Since its passage in 1990 there has been a decrease in research funding for studies of HAPs. Other potential problems include that once MACT regulations are established, it may be difficult to develop new technological approaches that will further improve air pollution control; that by treating all regulated HAPs similarly, no distinction is made between those that provide a higher or lower risk; and that there is a perverse incentive to use less well studied agents that are not on the existing list. As acting on the Precautionary Principle inherently imposes significant costs for what is a potentially erroneous action, additional scientific study should be required to determine if the precautionary action was successful. If we are to maximize the value of the Precautionary Principle to public health and the environment, it is crucial that its impact not adversely affect the potent preventive rôle of science and technology.     

Palynology,Biological Variation,and Pollen Analysis

Some examples from the current literature have been used for a discussion concerning the reliability of identification keys intended for general use. The rôle of the biological variation is stressed.     

Rôle of the midgut,crop, and maxillae of Bombyx mori in the production of cocoon-digesting enzyme

The rôle of the midgut, crop, and maxillae in the production and utilization of the cocoon-digesting enzyme was investigated in the silkworm, Bombyx mori.About a sixtyfold purified preparation of midgut protease was obtained by ammonium sulphate precipitation and column chromatography.Immunological studies by the agar diffusion method of Ouchterlony revealed that the crop and midgut proteases of the pharate adult are antigenically identical whereas that of the maxillary protease is different.From the results of extirpation experiments and previous studies it was shown that the midgut, crop, and maxillae play important rôles in the escape of moths from their cocoons.     

The direction of incident light and its perception in the control of pupal melanization in Pieris brassicae

The rôle of the direction of incident light in pupal melanization of the cabbage white butterfly, Pieris brassicae, was examined by exposing larvae during their sensitive period to various combinations of a light and dark background and of melanization inhibiting and promoting light. The results show that melanization is strongly controlled by the direction of the incident light.By blinding different eyes with black varnish, their rôle in the perception of the brightness contrast was studied. Nearly the same degrees of melanization are achieved as by corresponding arrangements of brightness contrast in the environment. Blinding the most ventrally located ocellus (No. 1) results in maximal melanization; blinding additional ocelli has no additional effect. On the other hand, no influence is observed if only the most dorsal ocellus (No. 6) is blinded.By coating the eyes with colours, their rôle in perception of melanization inhibiting and promoting light was investigated. Melanization is markedly influenced by light perceived via the ventral situated ocelli. In this case, the effect also depends on the number of ocelli involved. All effects may be explained by a mechanism which differentiates and transforms signals received through two or more ocelli, light perceived via the most ventral ocellus (No. 1) being the most important signal.An additional extraocular light receptor appears to be located dorsally in the head. This extraocular receptor can discriminate between different spectral ranges and perceive a brightness contrast (if the ocelli are blinded and the trunk is exposed to white illumination).     

Mise en evidence d'un RNA ribosomal de faible poids moleculaire dans les jeunes germinations de Raphanus sativus et de Phaseolus vulgaris

Un RNA ribosomal de faible poids moleculaire, distinct du RNA de transfert et analogue à celui qui a été identifie dans les cellules bactériennes et dans certaines cellules animates, a été mis en evidence chez les végétaux. Ce RNA ribosomal de faible poids moléculaire a été séparé du RNA de transfert. Les résultats sont discutés en relation avec des hypothèses récemment émises sur le rôle de ce nouvel RNA.     

Ultrastructure de l'ectoderme des tentacules labiaux et marginaux de Pachycerianthus fimbriatus McMurrich

In Pachycerianthus fimbriatus McMurrich, collar cells have been found in the ectoderm layer of marginal and labial tentacles. Villi, nematocytes, spirocysts, two types of mucous gland cells, and trypsinogen gland cells have been described. We have failed to discover special apical structures linked with the uptake of ferritin in solution. The rôle of apical villi and collar cells is discussed.     

Polysaccharides and food processing

The rôle of polysaccharides during processing and for the quality of foods is discussed. Starch is the most important energy source for man. Most other polysaccharides are not metabolized for energy, but play an important rôle as dietary fibres. Pectins, alginates, carrageenans, and galactomannans are discussed as functional food additives in relation to their structure and their rheological behaviour, stability and interactions. Endogenous polysaccharides of fruits and vegetables and in products derived from them are responsible for such phenomena as texture (changes), press yields, ease of filtration and clarification, cloud stability, and mouth feel. To achieve desirable properties, the action of endogenous enzymes on polysaccharides must be inactivated and/or exogenous enzymes added as processing aids. This is also true for overcoming haze phenomena in clear juices or to break down undesirable microbial polysaccharides. Dough properties for bread baking can be improved by enzymic breakdown of a restrictive pentoglycan network. Network formation may come about by oxidative coupling of phenol rings of ferulic acid bound to hemicelluloses by ester links. Gels may be made by inducing oxidative coupling in natural or synthetic systems. Stagnation in development of new polysaccharide food additives is ascribed to difficulties in obtaining government approval for food use.     

Neuromuscular junctions and L-glutamate-sensitive sites in the fleshfly, Sarcophaga bullata.

Sites have been located on retractor unguis and trochantal depressor muscle fibres of Sarcophaga which respond to iontophoretic application of l-glutamate. No such sites could be found on flight muscle fibres. Ultrastructural examination of the three muscles reveals differences between the muscles in the positions of the neuromuscular junctions. A correlation can be made between the sites of the neuromuscular junctions and the iontophoretically sensitive sites. The possibility of l-glutamate fulfilling a transmitter rôle in these muscles is discussed.     

Interactions Hyménoptères parasitoïdes – systèmes immunitaires hôtes: Les mécanismes «actifs» et «passifs» redéfinis

Résumé

Les Hyménoptères parasitoïdes ont développé de nombreuses stratégies de virulence pour permettre la survie de leur descendance aux dépens d’une gamme d’insectes-hôtes généralement restreinte. Cette diversité est telle qu’elle suggère l’existence d’autant de stratégies de virulence originales que de systèmes hôtes-parasitoïdes. Dans le domaine des interactions entre les parasitoïdes et le développement de leurs hôtes, il est admis que les stratégies parasitaires peuvent être scindées en deux grandes tendances, selon que le parasite régule ou se conforme à la croissance de l’insecte parasité. Nous proposons de redéfinir de manière similaire (stratégies de «régulation» ou de «conformité»), les stratégies parasitaires vis-à-vis du système immunitaire des hôtes, jusqu’à présent qualifiées d’ «actives» ou de «passives». En effet, de récentes études menées sur certains modes d’évitement de la réaction d’encapsulement (ectoparasitisme, «mimétisme» moléculaire) nuancent la nature «passive» de ces mécanismes de virulence et laissent présager d’une ère nouvelle pour la compréhension de leurs bases moléculaires. La présente revue s’attache donc: 1) à souligner la diversité des moyens employés par les Hyménoptères parasitoïdes pour se conformer à la réponse immunitaire de leurs hôtes ou pour la réguler; 2) à examiner les principaux facteurs parasitaires mis en ?uvre dans le cadre de ces stratégies ainsi que leurs cibles physiologiques; et 3) à évaluer l’intérêt fondamental et appliqué des recherches menées dans ce champs d’investigation.     

Chemical morphogenesis: Turing patterns in an experimental chemical system

Patterns resulting from the sole interplay between reaction and diffusion are probably involved in certain stages of morphogenesis in biological systems, as initially proposed by Alan Turing. Self-organization phenomena of this type can only develop in nonlinear systems (i.e. involving positive and negative feedback loops) maintained far from equilibrium. We present Turing patterns experimentally observed in a chemical system. An oscillating chemical reaction, the CIMA reaction, is operated in an open spatial reactor designed in order to obtain a pure reaction-diffusion system. The two types of Turing patterns observed, hexagonal arrays of spots and parallel stripes, are characterized by an intrinsic wavelength. We identify the origin of the necessary difference of diffusivity between activator and inhibitor. We also describe a pattern growth mechanism by spot splitting that recalls cell division.     

Contrôle de la sécrétion stéréomique dans les stolons d'un Crinoïde nouveau du Dévonien inferieur d'Algérie

The discovery of numerous distal stem fragments of Eurax marhoumensis n. sp. brings new data on the formation of the stolons and the control of stereomic secretion. The presence of primary fixations in the dististele demonstrates the composite nature of stolonifcrous scgmcnts. The creeping zone is formed by gradual incorporation of the lower columnals of the mesistele into the stolon. Stereom growth rings observed on weathered facets or transverse sections are markers of the morphofunctional evolution of the columnals during different growth stages. The fixation organs are true stereomic outgrowths without axial canal or Segmentation; they grow from a single columnal and remain in connexion with it. The morphology of stolons results partly from the topography of the substrate and partly from control by stereomic secretion which influences the columnal thickness. The introduction of wedge-shaped columnals in curves of the stem and on the development of fixation devices. Epizoan attachment (bryozoans, corals, crinoids) induces different stereomic reaction depending on the growth stage of the crinoid column. The stereom of the host may proliferate as a sheet, abortive ossicles or shapeless stercomic masses which tend to limit the growth of the epizoans and incorporate them in the column stercom. □Crinoid, column, morphology, stereomic secretion, Devonian, Algeria. Le découverte de nombreux fragments pédonculaires distaux d'Eurax marhoumensis n. sp. apporte des données nouvelles sur le processus de la formation des stolons et sur le contrôle de la sécrétion stéréomique. L'existence de fixations primaires dans la dististéle démontre la nature composite des segments stoloniaux. Les zones rampantes se forment par incorporation progressive des columnales de la partie inférieure du pédoncule dans les stolons. Les cernes de croissance du stéréome observées sur les facettes altérées ou sur les sections constituent des témoins de leur évolution morphofonctionnelle au cours des différents stades de la croissance. Les organes de fixation correspondent à de véritables expansions stéréomiques dépourvues de canal axial et de segmentation; ils bourgeonnent àpartir d'une seule columnale avec laquelle ils rcstent en conncxion. La morphologie des stolons résultc en partie de la topographie du substratum et du contrôle de la sécrétion stéréomique qui se traduit par I'ajustement de l'epaisseur des columnales, l'introduction d'articles cunéiformes dans les courbures et le développement des organes de fixation. L'implantation d'épizoaires (Bryozoaires, Coraux, Crinoïdes) provoque des réactions stéréomiques différentes suivant le stade de croissance du pédoncule du Crinoïde. Le stéréome de I'hôte peut proliférer sous formc d'une lame, d'articles abortifs ou d'amas difformes qui tendent a limiter le développement de I'épizoaire et à l'incorporer dans le pédoncule. □Crinoïde, pédoncule, morphologie. Sécrétion stéréomique, Dévonien, Algérie.     

A Turing test for collective motion

A widespread problem in biological research is assessing whether a model adequately describes some real-world data. But even if a model captures the large-scale statistical properties of the data, should we be satisfied with it? We developed a method, inspired by Alan Turing, to assess the effectiveness of model fitting. We first built a self-propelled particle model whose properties (order and cohesion) statistically matched those of real fish schools. We then asked members of the public to play an online game (a modified Turing test) in which they attempted to distinguish between the movements of real fish schools or those generated by the model. Even though the statistical properties of the real data and the model were consistent with each other, the public could still distinguish between the two, highlighting the need for model refinement. Our results demonstrate that we can use ‘citizen science’ to cross-validate and improve model fitting not only in the field of collective behaviour, but also across a broad range of biological systems.     

The acceleration of apolysis by the brain hormone in the silkworm, Bombyx mori

The rôle of the brain hormone as an activation hormone of the prothoracic glands in silkworm larvae was examined using decapitated larva of the fourth instar. The gland was activated by the brain hormone injected and induced early larval or larval-pupal apolysis.     

How well does Turing's theory of morphogenesis work?

In 1952 Turing published a paper which showed how under restricted conditions a class of chemical reactions could give biological patterns in diffusion-coupled cells. Although this theory has been much discussed, little has been learnt about the range and type of pattern it can generate. In order to do this and to see how stable the patterns are, we have examined the system in detail and written a computer program to simulate Turing's kinetics for two morphogens over various assemblies of cells. We find that on one-dimensional lines of cells, patterns can indeed be produced and that the chemical wavelengths follow all of Turing's predictions. The results show that stable repeating peaks of chemical concentration of periodicity 2–20 cells can be obtained in embryos in periods of time of less than an hour. We do find however that these patterns are not reliable: small variations in initial conditions give small but significant changes in the number and positions of observed peaks. Similar results are observed in two-dimensional assemblies of cells. On rectangles, random blotches are observed whose position cannot be reliably predicted. On cylinders whose circumference is less than the chemical wavelength, annular stripes are produced. For larger cylinders, blotches that lie very approximately on helices are generated; again sharp prediction of the detailed pattern is impossible.The significance of these results for the developing embryo is discussed. We conclude that Turing kinetics, at least in the simple cases that we have studied, are too unreliable to serve as the generating mechanism for features such as digits which are characterized by a consistent number of units. The theory is however more than adequate by these criteria to specify less well-defined developing patterns such as those of hair follicles or leaf organization. It is emphasized however that the Turing theory is quite unable to generate regulative systems, only mosaicpatterns can be produced.     

Studies on the nutrition and feeding preferences of Aplysia: Development of an artificial diet

An artificial diet made up principally of chemicals set in agar with a small amount of water extract of the green alga Ulva fasciata Delile has given good growth and spawn production in the sea hare Aplysia dactylomela Rang. The potential use of such a diet in the study of nutrition of sea hares and of other marine invertebrate herbivores is discussed and its possible rôle in identifying the characteristics of seaweeds which govern natural food choices in these animals is considered.     

The control of chitin deposition by ecdysterone in larvae of Bombyx mori

The effect of ecdysterone on the deposition of chitin in Bombyx larvae was examined. The chitin content in the abdomen decreased following hormone treatment to a value half that of the controls. Studies with ¹⁴C-glucose revealed that whereas controls exhibited a gradual decrease in the rate of ¹⁴C-glucose incorporation into chitin, the administration of ecdysterone resulted in a rapid fall in the rate of incorporation followed by a rise until ecdysis occurred. Chitin catabolism was estimated at 0·11 mg chitin/hr, based on the chitin content and incorporation rates. A dual rôle is indicated for ecdysterone in chitin metabolism, namely the activation of both synthetic and lytic systems.