bluuebunny/crossref_metadata_2025_split huggingface dataset:
CONCEPTS IN FUNGAL NUTRITION AND THE ORIGIN OF BIOTROPHY
Authors: LEWIS D. H. 
Published: January 2008

Summary1. Since use of the terms, symbiosis and obligate parasitism, is ambiguous, an attempt is made to re‐impose precision by a re‐evaluation of basic concepts.2. For symbiosis, there should be a return to a concept closer to that of de Bary's original, embracing those parasitic and mutualistic associations which involve permanent, intimate contact.3. Culturability should be abandoned as a criterion for classifying fungal behaviour.4. Instead of culturability, emphasis should be placed on the ecological and nutritional behaviour of fungi, permitting the recognition of five groups: obligate saprotrophs, facultative necrotrophs, obligate necrotrophs, facultative biotrophs and obligate biotrophs.5. Since environmental conditions can determine whether the nutrition of a fungus is biotrophic or necrotrophic, a scheme, speculative but amenable to experimental test, for the origin of biotrophy is proposed. This involves the interplay of alterations to patterns of translocation produced by fungally‐induced changes in hormonal balance in infected plants and catabolite repression of degradative enzymes of the fungus.6. The dependence of mutualistic symbiosis on the maintenance of biotrophy is stressed.7. Based on the nutrition of the diverse kinds of fungi involved in mycorrhizas, a re‐alignment of groupings of mycorrhizal associations is proposed. This directs research towards seeking generalizations within, and differences between, four clearly defined groups (sheathing, vesicular‐arbuscular, orchidaceous and ericaceous) instead of, as at present, within and between two (variously termed ectotrophic and endotrophic or ectomycorrhiza and endomycorrhiza), the second of which is highly artificial.Earlier drafts of the paper were read by Professors J. L. Harley, L. B. Thrower and S. D. Garrett, and Drs M. J. Carlile, B. C. Clifford, G. Hadley, P. M. Holligan, D. M. Losel and D. C. Smith. I am most grateful for their advice on specific points. Many, but not all, of their comments have been incorporated and I must stress that some views expressed, particularly with regard to the classification of mycorrhizas, are at variance with those of some of these colleagues.
THE HETEROSTRACAN FISHES
Authors: HALSTEAD L. BEVERLY 
Published: January 2008

Summary1. The heterostracan fishes were jawless, microphagous, devoid of paired fins and encased in a bony armour. The classification is based on the arrangement of the plates of the carapace — the primitive forms possessed a tessellated armour made up of numerous small polygonal plates. Several genera had a tessellated carapace ventrally but large discrete plates dorsally. All further groups are characterized by distinct patterns of plates which remain constant within each order. The proportions in some species suggest sexual dimorphism.2. A study of the superficial ornamentation reveals patterns of growth. From the primitive tessellated condition different evolutionary lines can be followed leading to the fusion of these small elements into large discrete plates. Among the latest group of heterostracans there was a secondary redevelopment of tesserae.3. Impressions on the inner surface of the plates of the carapace enable certain aspects of the internal anatomy to be reconstructed. The nasal sacs were double, the acousticolateralis system was primitive. The brain was little more than the nerve cord swollen in three places, there was no cranial flexure. Impressions of two pre‐otic somites were present, indicating that they had not migrated to form the extrinsic eye muscles. The branchial arches appear to have been of gnathostome type and in some genera spiracles were formed as an adaptation to a benthonic mode of life.4. Microscopic sections of the armour demonstrate the existence of four tissues: aspidin, dentine, enameloid and calcified cartilage. Aspidin was originally acellular but later became cellular; the organic matrix was first organized like dentine, but subsequently like bone. Furthermore aspidin was capable of remodelling. Dentine appears to have acted as a skin‐like tissue and was capable of regeneration. The significance of enameloid and calcified cartilage in the dermal armour is not well understood.5. Until the end of the Silurian the heterostracans inhabited marine waters but from the beginning of the Devonian they colonized the fresh‐water lakes and rivers of the Old Red Continent. One major group flourished in a large embayment on the edge of the Tungussian land mass. When the stratigraphical range and geographical distribution of the heterostracans is listed, evolutionary centres can be recognized and also migration routes: during the Upper Silurian the cyathaspids in the Canadian Arctic, the Lower Devonian pteraspids in Eastern Europe, the later Lower Devonian amphiaspids in north‐west Siberia (Tungussian Realm), and the Middle and Upper Devonian psammosteids in the Baltic province. Periods of migration from the Baltic to Scotland, the Timan, Ellesmereland, the Urals and Donbas have been documented.For the illustrations the author is indebted to Miss Jennifer Middleton and Mr John Smith.
THE CHITIN SYSTEM
Authors: RUDALL K. M. , KENCHINGTON W. 
Published: January 2008

SUMMARY

The view is supported that chitin is not found in Deuterostomia because of the absence of chitin synthetase, and is not found in higher plants because of the absence of glucosamine. In Fungi, control mechanisms are present affecting the synthesis of glucosamine; chitin is often present, but when it is absent this probably results from a failure to synthesize glucosamine.
A review of conformation maps for cellulose and chitin indicates the possibility of a slightly right‐handed twist in small groups of chitin chains.
The occurrence of α, β and γ‐forms of chitin in the peritrophic membranes of various insects is described. Gamma chitin seems to be the commonest form.
In several beetles, optical and electron‐microscope studies trace the formation of chitinous cocoon fibres from larval peritrophic membrane and define the discrete ribbon‐like nature of the, β chitin produced in the mid‐gut.
By studying apodemes it is found that orthopteroid insects are most varied, different molecular structures being present in levator, depressor and pretarsal tendons. By contrast, Hymenoptera and Coleoptera show very similar structures in all three apodemes as well as in other parts of the cuticle. Apodemes are regarded as sampling the cuticle at their varying points of origin; they provide especially favour able material for diffraction studies.
In arthropod cuticles there is evidence for the widespread occurrence of α chitin micelles which are three chains thick in the direction of the c axis. This is compared with the structure of γ chitin where the chains repeat in groups of three along the c axis.
Changes in the diffraction pattern are related to the series of proteins defined by Hackman. The chitin‐protein complex is not affected by water or neutral salt extrac tion, but is disrupted by treatment in urea.
Electron microscopy defines the unit of structure as a composite microfibril: a core of chitin surrounded by adsorbed proteins. This consists of ‘primary’ protein (often repeating as regular units along the fibrils) and a quantity of ‘satellite’ protein which obscures the imaging of the regularly arranged ‘primary’ protein. There are apparent ‘bridges' between the microfibrils.
New diffraction data give information about the size and arrangement of micro‐fibrils. These fibrils may be arranged in layers of ‘rods’, or as an hexagonal arrange ment of ‘rods’.
NEMERTINES AS POSSIBLE ANCESTORS OF THE VERTEBRATES
Authors: WILLMER E. N. 
Published: January 2008

Summary1. Primitive vertebrates have many characters which do not appear to be immediately represented in any obvious precursor.2. The hypothesis is put forward that creeping, or bottom‐living worms, classifiable as nemertines, attempted to recolonize the water by acquiring buoyancy, by swimming or both.3. Some of those that succeeded were able to do so by adopting a method of filter‐feeding made adequate by the development of gill slits, and then converting the proboscis rudiment into a semi‐rigid structure (the notochord) essential for oscillatory swimming movements. These were the precursors of the protochordates and the vertebrates.4. The acquisition of the ability to swim efficiently depended on the simultaneous development of distance receptors and the co‐ordination of the information that they provided with that provided by proprioceptors on the one hand and with the changing motor systems on the other. This entailed the development of a far more extensive nervous system, probably by incorporating into it much more of the dorsal ectoderm, and superimposing a primarily sensori‐motor system on to the more vegetative system already present in nemertines. This was achieved by elaboration of the placodal folding of the ectoderm which is characteristic of many nemertine embryos of the present day. In this manner a new central nervous system was combined and integrated with the existing more primitive ‘autonomic’ system and the cephalic ganglia of the nemertines became incorporated in the hypothalamus.5. The hypothesis suggests likely precursor tissues from which the following vertebrate structures could plausibly have developed: olfactory organ, lateral line system, anterior and posterior pituitary, thyroid, pineal organ, chloride‐secreting cells, oxyntic cells, notochord, urinogenital system, liver, and several others.6. The possible origins of the vertebrate eye, the somitic muscles, and some other fundamental features of the vertebrates are discussed. The evidence is still equivocal.7. The acquisition of filter‐feeding and swimming by nemertine worms would be expected to bring into operation a whole new system for the selection of appropriate genes and thus inaugurate a period of very rapid and probably divergent evolution, made even more rapid by the enormous advantages gained by animals acquiring efficient form‐vision together with rapid and well co‐ordinated movements. It is thought likely that the rapid evolution of this group of animals, which possessed few features conducive to clear fossil remains, accounts for the apparent break in the continuity of the story of animal evolution which has until now made the origin of the vertebrates such an enigma.8. It is suggested that studies of the proteins and secretions of the various organs of the nemertines and their comparison with those of the organs of the more primitive vertebrates might lead to the establishment of some important homologies.
DIFFERENTIATION OF NEUROBLASTOMA CELLS IN CULTURE
Authors: PRASAD KEDAR N. 
Published: January 2008

Summary1. An elevation of the intracellular level of cyclic AMP in neuroblastoma cells by prostaglandin E1 by an inhibitor of cyclic AMP phosphodiesterase, or by analogues of cyclic AMP irreversibly induces many differentiated functions which are characteristic of mature neurones. These include formation of long neurites, increase in size of soma and nucleus associated with a rise in total RNA and protein contents, increase in activities of specific neural enzymes, loss of malignancy, increase in sensitivity of adenylate cyclase to catecholamines and blockade of cells in G1‐stage of the cell cycle.2. Other agents, including serum‐free medium, X‐irradiation, 6‐thioguanine, cytosine arabinoside, methotrexate, 5‐bromodeoxyuridine, nerve growth factor, glial extract and hypertonic medium can induce some of the differentiated functions which are induced by high intracellular cyclic AMP.3. Morphological differentiation and differentiated biochemical functions can each be expressed in the absence of the other.4. Many of the responses of normal embryonic nerve cells to cyclic AMP are similar to those of neuroblastoma cells.5. A working hypothesis for the malignancy of nerve cells has been proposed. This states that an abnormal regulation of cyclic AMP phosphodiesterase activity which allows the expression of high amounts of this enzyme in neuroblastoma cells, may be one of the early lesions during a malignant transformation of nerve cells.6. A new experimental therapeutic model for the treatment of neuroblastoma is proposed. This involves the administration of sodium butyrate followed by the injection of l‐dihydroxyphenylalanine (l‐dopa) and prostaglandin E1 in the presence of cyclic AMP phosphodiesterase inhibitor.7. Recent studies have elucidated the control mechanisms of some differentiated functions in neuroblastoma cells. Cyclic AMP may become an important biological tool to probe the regulation and expression of many other differentiated functions in these cells. In addition to neuroblastoma cells, other neuronal culture systems are now available for investigating the problems of differentiation and maturation in nerve cells.
OOSORPTION IN INSECTS
Authors: BELL WILLIAM J. , BOHM MARGUERITE K. 
Published: January 2008

Summary1. The process of oosorption in insects is discussed with regard to the chronology of events which occur during resorption of oocytes and the role of their auxiliary cells.2. A theory of neuroendocrine control of oosorption is put forward, suggesting that cessation of juvenile hormone secretion is the most important factor leading to this degradative process in spite of the fact that oosorption and vitellogenesis can occur simultaneously.3. The diversity of behavioural, ecological and physiological factors which promote oosorption is discussed with an emphasis on differences and similarities among representatives of major insect groups, and the manner in which oosorption provides an ovipositional strategy.
THE MUSCULAR CONTROL OF VERTEBRATE SWIMMING MOVEMENTS
Authors: BLIGHT ANDREW R. 
Published: January 2008

SUMMARY

The succession of hypotheses on the role of myotomal muscle in the generation of swimming movements is described and the conventional concept of ‘waves of contraction’ is shown to be based on a number of misinterpretations.
The form of undulatory movements in vertebrate swimmers is characterized by the properties of the sinusoidal oscillation of parts of the body about the axis of progression. An important variable is the relative amplitude of the lateral oscillation of the head end, which can be large in some animals though usually small in most adult aquatic vertebrates.
Cinematographic records of swimming animals are examined to determine the forces involved in the generation of waves of bending. A simplified analysis suggests that undulation can be produced by alternation of tension development from side to side without ‘waves of contraction’ passing down the body.
Model systems which are able to flex from side to side are considered and two types distinguished ‐ the ‘resistance‐dominated’ which propagates waves of bending from centre to extremities, and the ‘stiffness‐dominated’ which does not. The type to which a model belongs is determined by the interrelationship of its stiffness and resistance, and the power with which it flexes.
A model homogeneous in its properties along its length cannot generate longitudinal movement by flexing from side to side. Some degree of unevenness from one end to the other is required for propulsion.
Observations of the movements of an ‘ostraciiform model’ are shown to discount previous theories of the hydromechanics of swimming by the oscillation of a stiff tail about a single pivot. A new interpretation is provided.
The majority of vertebrate swimmers behave like ‘hybrid oscillators’ which flex from side to side, ‘resistance‐dominated’ posteriorly and ‘stiffness‐dominated’ anteriorly.
The origin of the ‘waves of contraction’ suggested by electromyograms of swimming animals is traced to the requirement for a tail of variable stiffness for variable frequency of oscillation and to the need to reduce lateral oscillation of the head. Delayed contraction posteriorly and early contraction anteriorly contribute to these functions.
The ability of amphioxus to swim backwards and the inability of most vertebrates to do so is related to their structural organization in the form of ‘hybrid oscillators’.
Electromyograms are examined in the light of these mechanical models. A developmental sequence is described for the newt which illustrates the organization of the muscular control of swimming movements and may throw light upon the development of the neural mechanism.
REGULARLY ARRANGED PROTEIN ON THE SURFACES OF GRAM‐NEGATIVE BACTERIA
Authors: THORNE KAREEN J. I. 
Published: January 2008

SUMMARY

Many species of Gram‐negative bacteria carry a layer of regularly arranged sub‐units on the outer surface of their outer membrane. The subunits are arranged tetra‐gonally or hexagonally and have centre‐to‐centre spacings ranging from 4 to 35 nm, depending on the bacterial species.
The regularly arranged layer has been detected by electron microscopy in whole cells, cell walls, outer membranes and assemblies of isolated subunits. The regular arrays can be seen in intact cells by shadowing or freeze‐etching and, occasionally, in thin sections or after negative‐staining. Freeze‐etching and negative‐staining have been used to show the regular arrays in isolated cell walls and outer membranes. Negative‐staining is used in the examination of assembled isolated subunits.
Optical diffraction of electron micrographs provides more detailed information of the fine structure of the subunits in the regular array.
The regularly arranged surface layer can be removed by protein perturbants, by chelation of divalent cations with EDTA and EGTA, by cation substitution or by acidification.
The two surface subunits which have so far been purified have been found to be acidic proteins with molecular weights of 67000 (Acimtobacter 199A) and 140000 (Spirillum serpens).
In Acinetobacter 199A the surface protein is attached to the protein of the outer membrane through a salt bridge involving Ca2+ or Mg2+. Evidence exists that there may be a similar mode of attachment in other species.
Isolated surface proteins from Acinetobacter 199A and from Spirillum spp. have the ability to reassemble into the same pattern as that seen on the bacterial surface, either in isolation or in the presence of cell‐wall fragments to act as nucleating agents. Self‐assembly of Acinetobacter 199A a‐protein requires chloride ions.
Acinetobacter 199A a‐protein can only be incorporated onto the bacterial surface if an intact lipopolysaccharide membrane is formed first to receive the intrinsic membrane proteins to which the a‐protein attaches. Impairment of lipopolysaccharide synthesis by bacitracin prevents incorporation of a‐protein and other membrane proteins into the outer membrane.
Continuing incorporation of pre‐formed radioactive a‐protein into the outer membrane in Acimtobacter 199A can be detected for 10 min after transference from radioactive to non‐radioactive growth medium.
Spirillum metamorphum, Flexibacter sp. and Acinetobacter 199A synthesize more surface protein than is required to cover the cell surface. The excess is secreted into the growth medium.
The regularly arranged surface protein of Acinetobacter 199A provides partial protection against isolated lysosomal proteinases from polymorphonuclear leucocytes. Spirillum spp. is protected from Bdellovibrio invasion by the surface protein.
Secreted a‐protein from Acimtobacter 199A has phospholipase A, activity. No phospholipase activity can be detected when the a‐protein is bound to the bacterial surface.
INTRASPECIFIC NEST PARASITISM IN BIRDS
Authors: YOM‐TOV YORAM 
Published: January 2008

Summary(1) The incidence of intraspecific nest parasitism in birds is reviewed. This phenomenon can be identified by various methods, ranging from biochemical examination of protein and enzyme polymorphisms to observations on the sequence of appearance of eggs in the nest as well as on the shape and colour of the eggs. The phenomenon has been reported for at least 53 species (Table I), mostly among precocial birds.(2) The evidence suggests that the parasites are (a) young, unmated birds, (b) females which have lost their nests and (c) mated females which also lay in the nests of other females. High proportions of such females, and scarcity of suitable nest sites increase the rate of parasitism.(3) Breeding success in parasitized nests is reduced by factors such as egg loss, desertion, inefficient incubation, reduced clutch size and late layings. The upper limit of the rate of intraspecific parasitism is discussed. It is argued that its incidence will be higher in the tropics than in extreme zones, for example, high latitudes and deserts, because there is higher synchronization of breeding in the latter, and increased predation in the former zones. Also, it will be more common in species which lay large clutches, such as precocial species.
CELL BEHAVIOUR AND MOLECULAR MECHANISMS OF CELL‐CELL ADHESION
Authors: GARROD D. R. , NICOL A. 
Published: January 2008

Summary1. At the behavioural level, cell adhesion is generally non‐specific. The search for molecular mechanisms of adhesion should be conducted on this basis.2. Cells in general, be they from slime moulds or vertebrate epithelia, possess multiple molecular adhesive mechanisms. In epithelial cells this is shown by the number of their different ultrastructurally recognizable intercellular junctions. Elucidation of the structure and composition of such intercellular junctions will make a valuable contribution to the understanding of cell adhesion.3. The measurement of cell adhesion is fraught with difficulties. Commonly used assays by aggregation cannot give a true representation of the normal adhesive interactions of cells in tissues, and the results they yield must be interpreted with caution. This is because it takes dissociated tissue cells up to 24 h to develop their full adhesiveness after making initial contact.4. Cell‐cell adhesion probably depends largely upon the interaction of complementary molecules on adjacent cell surfaces. Glycoproteins seem the most likely candidates but, as yet, there is no compelling evidence in any individual case and mechanisms of cell adhesion still remain obscure.