bluuebunny/crossref_metadata_2025 huggingface dataset:
CAROTENOPROTEINS IN INVERTEBRATES
Authors: CHEESMAN D. F. , LEE W. L. , ZAGALSKY P. F.
Published: January 2008

True carotenoproteins are defined as complexes in which a carotenoid and a protein are in stoichiometric combination. Very few carotenoproteins have been purified, but their presence in extracts may often be presumed from spectroscopic evidence. Carotenoids have been found in stoichiometric association with simple proteins, lipoproteins and glycoproteins. Many lipoproteins also occur in which carotenoids form part of the lipid prosthetic group. Although the relationship between the carotenoid and the remainder of the complex may in these cases not appear to be stoichiometric, it often shows some evidence of selectivity.

Carotenoproteins are widely distributed among the invertebrate phyla. They are found mainly in exoskeleton or ectoderm and in eggs and ovaries. Their isolation by standard techniques of protein chemistry is facilitated by their characteristic spectral properties.

The ease with which carotenoid prosthetic groups are removed from apoproteins suggests that covalent linkages are not involved in the complex formation. The union of carotenoid with apoprotein has been shown, in at least two cases, to stabilize the carotenoid against photo‐oxidation and the protein against denaturative changes of tertiary structure. In crustacyanin, the carapace pigment of the lobster, there is clear evidence that the carotenoid is responsible for establishing the very complex quaternary structure.

Only astaxanthin, astaxanthin esters and canthaxanthin have been unequivocally identified as carotenoid prosthetic groups of true carotenoproteins. Experiments in the specificity of interaction of a series of carotenoids with the apoprotein of crustacyanin have indicated the requirement of one or both of the 4‐ and 4′‐keto groups of the carotenoid for interaction with the protein.

It is suggested that, at least in this case, the carotenoid‐protein interaction might occur between carotenoid keto groups and basic residues of the protein in such a way as to provide a lock on the tertiary configuration.

Carotenoproteins may participate in a variety of functions including protective coloration, photosensitivity, electron transport and enzymic activity. They appear, furthermore, to play some part in development.
BIOCHEMICAL STUDIES ON THE PRODUCTION OF MARINE ZOOPLANKTON
Authors: CORNER E. D. S. , COWEY C. B.
Published: January 2008

1. Phytoplanktonic algae vary in their value as food for zooplankton and no single algal food can meet the full nutritional needs of zooplanktonic animals. Perhaps this is because optimal amounts of essential micronutrients are not all present in any one alga. The dietary requirements of planktonic Crustacea, as far as they are known, bear some resemblance to those of vertebrates.

2. The proteins of phytoplankton are similar in amino acid composition to those of zooplankton. This circumstance should favour efficient synthesis of protein by the animal, for assuming amino acids are all released in the gut and absorbed at approximately the same rate, they will be presented to the tissues in roughly the right relative amounts for protein formation.

3. Zooplankton are able to alter the characteristics of the fatty acids present in their diet by elongating the carbon chain length and by increasing the degree of unsaturation.

4. Measurements of phosphorus and nitrogen excretion indicate that zooplankton are metabolically very active. Some of the very high rates of phosphorus excretion are questioned and it is suggested that some portion of the phosphorus compounds liberated by zooplankton have passed straight through the gut without being assimilated. It is unlikely that all forms of organically bound phosphorus are equally rapidly assimilated and turned over by zooplankton.

5. Estimates of the rate of ammonia excretion by zooplankton differ markedly. This may be a matter of size/surface area of the animals concerned—smaller animals excreting more rapidly than larger animals. It has been claimed that a‐amino nitrogen is released in considerable quantities by zooplankton but the evidence is not yet compelling.

6. There is considerable disagreement on the efficiency of food assimilation and conversion by zooplankton. One view is that irrespective of the quantity of phyto‐plankton ingested assimilation is uniformly high. The opposing view holds that when rapid ingestion of phytoplankton occurs the percentage assimilated falls. More information on the feeding behaviour of zooplankton and on the physiology of their digestive processes is required before this controversy can be satisfactorily resolved.
SELECTION and QUANTITATIVE CHARACTERS IN FIELD CROPS
Authors: WALKER J. T.
Published: January 2008

1. It is vital that there should be no decrease in the rate of improvement of crop plants. In drafting the background to the inheritance of quantitative characters it is suggested that greater understanding of genetic mechanisms is needed rather than further increase in biometrical complexity. Selection is a very powerful force; it could be used to conserve genetic variation whilst effecting useful change.

2. Various breeding techniques, examined in a framework of directional, stabilizing and disruptive selection, are found to be tied to certain crops. Breeders of self‐fertilizing plants handle quantitative variation differently from those working with outbreeders.

3. Physiological analysis and partitioning of characters have not in themselves made large contributions to solving problems caused by complex traits, but both have been informative in conjunction with biometrical studies. In some circumstances more use could profitably be made of selection indices.

4. Heterozygote advantage and genetic balance play major parts in stabilizing selection. Modal selection can sometimes lead to increased fitness, conforming with the concept of genetic homeostasis.

5. Disruptive selection has apparently operated during the evolution of crop plants. To be beneficial to breeders it should be multidirectional; intercrossing of peripheral lines might then form ‘springboard’ populations allowing further advance from selection plateaux.

6. As the boundaries of cultivation are extended so the need will increase for plant populations with inherent stability of performance. Few crops are yet amenable to the production of F1 hybrid seed, so polygenes should be manipulated to form balanced, heterozygous adaptive complexes. Systems of selection must be refined to deal effectively with the heterogeneous populations from which such complexes are likely to arise.

7. Studies on composite crosses and related projects tie in well with other work on selective forces in adaptation. New allopolyploids offer hope in some plant groups, but induced mutation is of restricted value.

8. Cryptic variation and selection can be important in many breeding methods, and should be considered when dealing with quantitative aspects.

9. Changes in locality can reveal startling amounts of unsuspected variability: such ‘environmental segregation’ could be harnessed, for example, by alternation of selection centres when breeding for general adaptability.

10. Persistence of variation, which may occur through selection favouring hetero‐zygotes despite strict inbreeding, is also considered in terms of heterozygous gene complexes. Tightness of linkage is the key to the durability and behaviour of super‐genes, and analysis of the simpler ones could lead to better understanding of the vastly complicated systems controlling fitness and productivity.
PASSIVE IMMUNITY AND ITS TWSFER WITH SPECIAL REFERENCE TO THE HORSE
Authors: JEFFCOTT L. B.
Published: January 2008

1. There are relatively few references in the literature on the transfer of passive immunity to the newly born foal. Transmission of immunity has been established as being post‐natal in origin. At birth the serum is apparently agammaglobulinaemic and only trace levels of antibody are detectable. Peak levels of immunity are reached a few hours after ingestion of colostrum.

2. Immune proteins derived from the dam's serum are selectively concentrated in the mammary gland before parturition. In the horse the predominant immuno‐globulins of colostrum are IgG and IgG(T).

3. The mechanism of absorption of colostral proteins by the newborn animal is complex and there are considerable species differences. In newly born ungulates the uptake is effected into specialized epithelial cells of the small intestine by pinocytosis. This is followed by transfer of the proteins across the cell, their extrusion into the lamina propria and into the lymphatics before they reach the systemic circulation.

4. The absorption of macromolecules occurs without degradation in neonatal ungulates, is non‐selective and can be enhanced by solvent factors in the colostrum. The duration of transfer is influenced by stress and the administration of adrenal corticoids.

5. The period of absorption in ungulates is short (< 48 hr.) compared to that in rats and mice (13–21 days). In the foal the small intestine is permeable to macro‐molecules for less than 24 hr. after birth.

6. After birth there is a gradual decline in the concentration of protective antibody to insignificant levels by 5–6 months. The foal shows evidence of active immunity from one to 3 months of age.

7. A transient proteinuria is detectable in newly born animals fed colostrum soon after birth. This proteinuria occurred in two phases, initially there were rising levels of urinary protein followed by sharply declining levels to 36 hr. of life. Feeding high protein colostrum during and after the time of intestinal closure did not prolong the period of proteinuria. The constituents of the proteinuria were almost exclusively low molecular weight proteins of milk of colostral origin, β‐lactoglobulin and α‐lact‐albumin.

8. The importance of neonatal infections in the foal has been well documented but there are few accounts of its relation to passive immunity.

9. A natural immunological incompatibility, haemolytic disease, occurs in the horse. The disease can be diagnosed in the mare in late pregnancy and prevented in the foal by completely withholding the dam's colostrum for 24 hr. of life.
OBLIGATE PARASITISM BY PHYTOPATHOGENIC FUNGI
Authors: SCOTT K. J.
Published: January 2008

1. This review is concerned with the obligate parasitism of the downy mildew, powdery mildew and rust fungi.

2. Mechanisms which determine resistance and susceptibility are incompletely understood. The three possibilities so far advanced, namely, hypersensitivity, phyto‐alexins and nutrition are all inadequate to explain specificity. It is postulated that compounds carrying specificity are released by the invading pathogens and the interaction of the compounds with specific sites in the host cell determines whether a successful relationship is established. This hypothesis is based on the observation that host and pathogen protoplasts do not come in direct contact with each other and cells removed from the invading pathogen are affected. It should be possible to investigate this question now that some rust fungi have been cultured axenically.

3. Invasion of host tissue by these pathogens leads to alteration in host metabolism. Respiration rates and the activity of the pentose phosphate pathway are enhanced. Possible mechanisms for the reoxidation of NADPH by molecular oxygen are discussed. In the later stages of infection, photosynthetic activity is decreased and this decrease is coupled to the enhanced activity of the pentose phosphate pathway through NADPH availability.

It is still not clear whether photosynthetic activity is increased or decreased during the early stages of infection. Nutrients from other parts of the plant accumulate at sites of infection, resulting in retarded growth of the host. Possible roles of hormones in nutrient mobilization and ‘green island’ formation are discussed.

Changes in intermediary metabolism can be correlated with changes in amounts of nucleic acids in infected host cells. Chloroplast polysomes and ribosomes decrease during the early stages of infection but cytoplasmic ribosomes increase during patho‐genesis. This increase more than compensates for the decrease in chloroplast ribosomes resulting in an overall increase in cellular RNA.

4. Some members of the Pucciniaceae and one member of the family Melamp‐soraceae have now been cultured axenically. Nutritional studies indicate that these fungi are relatively non‐specific with respect to their carbohydrate and amino‐acid nitrogen sources but do have a specific requirement for either cysteine, methionine or homocysteine. Essential metabolites such as cysteine and cysteine‐containing peptides move from hyphae into the medium and these may be important in amino‐acid transport.

Two stages in the development of axenic rust cultures are still imperfectly understood ‐ the transition from germ tube to saprophytic mycelium and the fate of the colonies once formed. Further knowledge of the factors which control these stages may well suggest approaches to the axenic culture of other groups of obligately parasitic fungi.
CONCEPTS IN FUNGAL NUTRITION AND THE ORIGIN OF BIOTROPHY
Authors: LEWIS D. H.
Published: January 2008

1. 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

1. 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

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

1. 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

1. 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

1. 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

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

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

(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

1. 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.
THE ORGANIZATION AND EVOLUTION OF MICROTUBULAR ORGANELLES IN CILIATED PROTOZOA
Authors: LYNN DENIS H.
Published: January 2008

(1) Ciliated protozoa are viewed as unicellular organisms structured in a hierarchy of organizational levels that include the macromolecular, suborganellar, unit organellar, organellar complex, and organellar system.

(2) The ciliate cortex is divided into two major functional regions, the somatic region and the oral region. The fundamental component of the cortex is an organellar complex, the kinetid, whose organizing centre is the kinetosome with which are associated three fibrillar associates diagnostic of ciliates. These three fibrillar associates are the periodically striated kinetodesmal fibril and two microtubular ribbons, the transverse and postciliary ribbons.

(3) Somatic and oral kinetids are found to be of three major types: monokinetids are composed of one kinetosome and its fibrillar associates; dikinetids are composed of two kinetosomes and their fibrillar associates; polykinetids are composed of more than two kinetosomes and their fibrillar associptes.

(4) The mechanisms underlying kinetid function and development remain largely unexplored. Research into the molecular biology and ultrastructure, especially of mutant forms, should provide basic insights in the near future.

(5) The conservation of kinetid structure across major phyla of organisms suggests that this subcellular structure should be useful in phylogenetic analysis despite the concepts of ‘chemical identity’ and ‘organic design’.

(6) The evolutionary rate of change of oral features is greater than that of somatic features, probably due to developmental and ecological factors. Nevertheless both cortical regions are constrained by the phenomenon of structural conservatism; that is, the conservation of structure through time is inversely related to the level of biological organization.

(7) Eight major groupings of ciliate species are recognized, based on ultrastruc‐tural features of the cortex. Several examples of differences between these eight groups and the groups presently recognized are discussed.
SPATIAL ORDER IN MICROBIAL ECOSYSTEMS
Authors: WIMPENNY JULIAN W. T.
Published: January 2008

(1) It is suggested that microbiologists are concentrating too much at present on homogeneous laboratory models such as the chemostat to simulate natural microbial ecosystems, which are not usually homogeneous but structured in time and space.

(2) Natural microbial ecosystems that are spatially heterogeneous are reviewed and discussed.

(3) Microbial interactions are briefly discussed in so far as they are relevant to spatially organized ecosystems.

(4) Concepts such as ‘niche’ and ‘habitat’ are defined and discussed in terms of their applicability to microorganisms growing at specific points in solute gradient systems. The definitions currently accepted lack precision because they do not take into account the importance of spatial and temporal coordinates. Use of the words ‘compartment’ and ‘domain’ is advocated. The former corresponds to a cell, the latter to a region around it where the compartment has some influence, acting either as a source or as a sink for particular solutes. The terms ‘niche’ and ‘habitat’ are redefined for the activity domains of a compartment and the habitat domains of the ecosystem. The importance of the vectorial flow of solutes is stressed.

(5) Current methodology in microbial ecology is briefly reviewed.

(6) Methods specifically designed for investigating heterogeneous ecosystems are described, These include: (i) The gradostat, a system of interlinked culture vessels allowing the establishment of steady‐state bidirectional solute gradients. (ii) Percolating columns. (iii) Capillary methods. (iv.) The thin film fermenter. (v) The use of two‐dimensional diffusion plates or stopped time‐dependent gradient plates. (vi) Gel‐stabilized diffusion models established vertically in glass containers such as beakers. (vii) The use of one‐dimensional gradient‐plate techniques to determine the habitat characteristics of different microbial species. (viii) Investigations into naturally structured systems such as the bacterial colony.
ADAPTIVE STRATEGIES OF COLONIZING ANIMAL SPECIES
Authors: Parsons P. A.
Published: January 2008

1. An understanding of the adaptive strategies of colonizing animal species depends upon an integration of population genetics and ecology, but behavioural components should not be ignored especially higher in the phylogenetic series than insects.

2. An ecologically marginal habitat from which colonists are derived can be regarded as one in which physical stresses of climatic origin tend to be variable and extreme, so that resources are unpredictable and short lived. Prerequisites for genetic analysis are therefore phenotypes relatable to the r K continuum of adaptive strategies. These can be called ‘ecological phenotypes’.

3. Ecological phenotypes include tolerances to environmental stresses, development time, and resource utilization variability. Such phenotypes enable distinctions to be made between colonizing species and non‐colonists. For example, colonizing species have ecological phenotypes incorporating high resistance to physical stress, rapid development time, and the exploitation of an array of food resources. They are ecologically versatile generalists. This includes the use of ethanol as a resource in Drosophila.

4. There is a substantial literature on variation in central and marginal populations based upon gene and chromosome polymorphisms. Most data show a reduction of chromosome polymorphisms and of lethals and semilethals towards the margins, but no equivalent reduction in enzyme polymorphisms. Widespread species tend to have low levels of chromosome polymorphisms as in marginal populations, but enzyme polymorphism levels vary too much among species for meaningful interpretations. Since these are genotypic assessments not directly relatable to the field situation, the somewhat unsatisfactory nature of these data from the interpretative point of view is understandable. In addition, the fundamental issue is not the variability of the genome, but the nature and role of loci controlling ecological phenotypes.

5. Ecological phenotypes can be analyzed at the population level with isofemale strains as the starting material. In theory, genetic activity can then be localized to the chromosomal and even genic levels in a species such as D. melanogaster. Isofemale strain studies in D. melanogaster are interpretable in terms of the r K continuum, and so reflect adaptive strategies in nature.

6. It is highly likely that the genetic architecture of ecological phenotypes of marginal populations mainly comprises a few additive genes of relatively large effect. This is an architecture permissive of rapid adaptation to new habitats, provided that the appropriate genes are present. Discussions of speciation via the founder principle, a colonization event in itself, have invoked a similar explanation.
THE TRANSPORT AND FUNCTION OF SILICON IN PLANTS
Authors: RAVEN JOHN A.
Published: January 2008

A number of lines of evidence (Mr, number of ‐OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic PSi(OH)4of about 10‐10m s‐1in the plant cell plasmalemma. While relatively low, such a PSi(OH)4could maintain the intracellular concentration of Si(OH)4equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super‐saturated solution or the quantity of SiO2required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)4due to the intrinsic permeability of lipid bilayers to Si(OH)4is never more than 10% of the cost of silicification.

In vascular land plants the entry of Si from the soil into the xylem can involve a flux ratio (mol Si/m3water) that is less than (e.g. Leguminoseae) equal to (e.g. many Gramineae) or greater than (e.g.Oryza, Equisetum) the concentration (mol m‐3) in the bathing solution. Even the low influx of the Leguminoseae cannot be accounted for by the ‘lipid solution’ value of PS(OH)4, but requires entry coupled (phenomenologically) to water influx with a reflexion coefficient of about 0.9. The situation in most Gramineae is described by such a coupling with a reflexion coefficient near O, while the accumulation of Si (relative to water) inOryzaandEquisetuminvolves an apparent reflexion coefficient which is negative, i.e. an active transport system stoichiometrically related to water flux. Even in Leguminoseae with a transpiration‐stream concentration of Si(OH)4of only 20 mmol m‐3(cf. the soil solution at 200 mmol m‐3), the fact that only I % of the water in the xylem is retained in the plant means that Si(OH)4at transpirational termini approaches saturation; super‐saturation, and precipitation of SiO, occurs in Gramineae andEquisetum.SiO2precipitation occurs mainly near transpirational termini but can also occur in the xylem vessels and endodermis of roots, for example. Si(OH)2mobility in the phloem seems to be very restricted.

The energy costs of SiO2relative to organic compounds as structural and defensive materials are in the ratio of 1:10‐1:20 (on the basis of weight of material). The relative rarity of SiO2as a structural material is discussed in the context of the evolution of Si(OH)4‐transport mechanisms.
ADHESION IN BYSSALLY ATTACHED BIVALVES
Authors: WAITE J. HERBERT
Published: January 2008

The byssus is a structure produced by marine bivalve molluscs to adhere, usually permanently, to substrata under water. As the adhesion of synthetic polymers to surfaces is predictably compromised by the presence of water, particularly bulk water, it is of particular interest to discover the mechanism of byssal adhesion. In most species, the byssus consists of at least four essential components: acid mucopolysaccharides, adhesive protein, fibrous proteins, and an oxidative enzyme, polyphenoloxidase. The function of the mucopolysaccharide component is still uncertain, but it can conceivably be used by the animal as a temporary adhesive, a surface modifying agent, and/or a stabilizing filler for the permanent adhesive. The adhesive protein known as the polyphenolic protein in Mytilus is but a thin plaque applied to the substrate surface by the foot of the animal. The molecular and physical properties of this adhesive protein conform remarkably well to what one expects of an ideal synthetic polymer, i.e. high molecular weight, abundance of large and polar side chains, near‐zero surface contact angle, and total water‐insolubility after setting. The fibrous proteins constitute the major portion of the thread or ribbon‐like material connecting the animal to the adhesive plaque on the substrate surface. These proteins are packed in ordered crystalline arrays, e.g. β‐pleated sheet and collagen helix (in mytilids) as is to be expected from structural tensile elements of Nature. The enzyme polyphenoloxidase is presumed to induce intermolecular cross‐linking of proteins in the fibrous and adhesive portions of the byssus. In Mytilus the natural substrates of the enzymc may be the dopa‐containing polyphenolic protein and accessory gland protein.