摘要:

SummaryThe term ‘Blochmann body’ was originated by Wheeler in 1889 for bacteria‐like particles in the cytoplasm of cockroach eggs. These particles can be traced during embryonic development to definitive somatic cells, the mycetocytes. These and similar particles of other insects have so far not been cultivated in bacteriological media nor injected into host animals to produce either pathological or benign infections. Their structure and composition indicate them to be evolutionary descendants of free‐living micro‐organisms; operationally, they appear to belong to the class of cell particles designated by Lederberg (1952) as plasmids.Genetic studies have shown the Blochmann bodies to be transmitted through the maternal line. Their presence in the egg cytoplasm at some stage in oocyte development is easily demonstrated, but studies by a number of workers have so far yielded a variety of conflicting claims or suggestions as to how the particles get into the germ cells or oocytes.The Blochmann particles of cockroaches, besides existing in the mycetocytes and eggs, occur embedded in a dense tangle of microvilli which are extensions of the plasma membrane of young oocytes.Essentially particle‐free strains of cockroaches can be produced by feeding aureo‐mycin or high levels of urea, or by withholding manganese. The effect is produced only by treating females, and is delayed one generation. In generations following the first (symbiont‐free) generation, the Blochmann symbionts gradually reappear, suggesting that elimination was not absolute.Blochmann bodies in both the mycetocytes and the ovarioles of the cockroach carry out oxidative metabolism, as indicated by their ability to reduce tetrazolium. Glycolysis has not been demonstrated.The generalization that symbionts of the Blochmann type represent an adaptation to compensate for dietary deficiencies is inapplicable, since deficiencies have not been demonstrated for the diets of cockroaches, weevils, or homopterans—the major insect groups in which the symbionts occur. The symbionts of cockroaches and homopterans appear to be involved in the utilization of nitrogenous waste products in synthetic metabolism.In most instances the Blochmann bodies lack the central nucleoid body characteristic of the growing phase of free‐living bacteria, thus resembling the Kappa and Mu particles ofParameciumand the endosymbiont of the protozoanCrithidia oncopelti. Both histochemical tests and electron‐microscope studies indicate a DNA component that is widely dispersed within the particle.Blochmann bodies are without internal cristae. The cockroach symbionts contain muramic acid, a diagnostic feature of the cell wall of bacteria. Response to various nuclear and cytoplasmic reagents is intermediate between those of typical mitochondria and free‐living bacteria. The envelopes of the Blochmann particles are generally thinner than those of free‐living bacteria.The function of plasmids of the Blochmann type may be that they, like the bacteroids of theRhixobium‐legumesymbiosis, extend the range of metabolic potential of the host cell by a process of mutual host‐symbiont adjustment. Possible roles could be subsumed under the headings of bacteria‐like, mitochondria

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1968.tb00961.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SummaryCalcium as a plant nutrient is characterized by its relatively high content in the plant coupled with a requirement not much higher than that of a micro nutrient element and an exceedingly uneven occurrence in soils. The difficulties in defining its actions are accentuated by a weak biochemical activity. In ecological conditions the secondary consequences of variations in calcium content may be more striking than the direct ones.Electron‐microscopical studies have revealed that calcium is required for formation and maintenance of lamellary systems in cell organellae, a fact which might suffice to explain its indispensability for meristematic growth.Calcium is required for cell elongation in both shoots and roots; the common experience that it inhibits shoot elongation is certainly due to calcium additions far above actual requirement.It must be assumed for a rational interpretation of cell elongation that the fundamental mechanism is the same in shoots and roots. The one action which can be ascribed with certainty to calcium is a stabilizing of the cell wall with an increase in rigidity, an effect which, with over‐optimal supply, may lead to growth inhibitions. The function is, however, necessary for the normal organization of cell walls. Calcium has, on the contrary, no significant effect on the synthesis of cell wall compounds but appears to act on their proper incorporation into the cell wall.The growth‐active calcium may be bound not only to pectins but also to proteins and nucleoproteids in or in close contact with the cell wall.The supposition that calcium interacts directly with auxin in the cell wall has not been verified and does not seem very probable. There are reasons to believe that the points of action of calcium and auxin in the cell wall differ, auxin inducing growth by wall loosening and calcium establishing new wall parts.For submerged organs it may be necessary to consider an indirect effect of calcium on growth by its regulation of cytoplasmic permeability and thus affecting the exudation of growth‐active compounds.The ecological problem is to characterize calcifuges (acid soil plants) from calcicoles (base soil or calcareous soil plants). Growth inhibitions on acid soils depend upon poisoning by A13+and Mn2+. Opinions differ as to what extent this can be antagonized by calcium. Lime‐induced chlorosis in calcifuges depends upon iron deficiency or iron inactivation in the plant. No acceptable explanation is given, but it might be related to an interaction of calcium carbonate, phosphorus, and iron. A hypothesis that it is linked to formation of organic acids is not tenable in the given form.Plants react to the calcium ions in the concentrations found in soils. Calcifuges have a low calcium‐optimum for growth and show growth inhibition at high concentrations. Calcicoles have a high optimum for growth. Calcifuges are resistant to aluminium poisoning. Attempts made to explain the differences in calcium uptake and generally in salt uptake are tentative only, and relevant data

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1968.tb00962.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Summary1. Procaryotic motility mechanisms are more difficult to investigate than those of the generally larger, hence more easily observable, eucaryotic forms. Furthermore, although the function—namely translational locomotion—is the same, the biomechanisms by which this end is accomplished may be, in fact, quite distinct in the two forms.2. Observational techniques for studying procaryotic motility are relatively crude and qualitative. Progress toward a greater understanding of motility phenomena will be made correlative with advances derived from devising specific techniques involving approaches adapted from electrical engineering, biophysics and cybernetics.3. There is a great amount of information at hand concerning the qualitative and quantitative chemical composition of procaryotic flagella, but there is no assurance that preparatory techniques include either the entire organelle on the one hand, or do not introduce subtle errors on the other hand. Similarly, the structural features of flagella as derived from electron‐microscope studies of fixed preparations may be themselves influenced by the techniques employed to reveal them.4. Chemotactic responses of bacteria have been noted almost since the beginning of bacteriology as a formal scientific endeavour, yet the study of transduction of environmental stimuli, using motile bacteria as experimental subjects, is a relatively recent development. We have proposed that the cytoplasmic membrane may act as a non‐specific receptor‐transmitter of such signals in motile bacteria. If this is found to be the case, perhaps a sensory code may be more amenable to discovery here than with more complex forms of organisms.5. Knowledge of the physical aspects in procaryotic flagellar movement is extremely fragmentary. There is some information on the movements of living functional flagellar fascicles, but this form of movement of an individual flagellum is purely speculative. We have proposed that the procaryotic flagellum is a rigid or semi‐rigid helix, which does not transmit helical waves of contraction, and that its movements are governed by a specialized area of the cytoplasmic membrane. The flagellum may rotate or wobble within the flagellar basal bulb to produce the motion necessary for propulsion. This view ‘explains’ many of the known properties of procaryotic flagella.6. The basis of gliding motility remains unknown even after a great deal of experimental work. In our view, the secretion of slime is necessary for adhesion to a solid surface, and movement is believed to be mediated by a mechanism involving contractile waves.7. Studies on procaryotic motility may yield valuable information on certain areas of general biological interest. Among these are: (a) the transduction of environmental stimuli and the sensory code; (b) the development of reproducible observational techniques for quantitative data on the hydrodynamic and biophysical parameters of cell motion in procaryotic forms; (c) the phenomenon of unicellular ‘behaviour’ and the survival value and evolutionary significance of motility; and (d) the elucidation of the mechanism of gliding with perhaps an assessment of its utility in a wide variety of micro‐organisms. All of these areas are ripe for imaginative and innovative experimentation; let us hope i

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1968.tb00963.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Summary1. Although the classical models of biomembranes have emphasized the lipid and protein nature of these structures, a small quantity of carbohydrate is present as glycoprotein and glycolipid in animal cell membranes. In this article an attempt has been made to indicate that such carbohydrate materials should be considered in any complete model of animal cell membranes.2. Various techniques that have demonstrated the presence of glycoproteins in animal cell membranes have been discussed here. In particular, cell electrophoresis, especially when the measurements are combined with specific enzyme treatments of the cells, has indicated that the net negative surface charge on intact viable cells is mainly due to sialic acid‐containing glycoproteins and not as previously thought to ionizable phosphate groups associated with a complex phospholipid system.3. Membrane‐bound antigens are complex carbohydrate‐containing macro‐molecules whose antigenic activity is principally associated with the configuration at terminal positions on the carbohydrate chains. Enzymic degradation of the glycoproteins of the intact plasma membrane of cells, especially erythrocytes, causes profound changes in the immunological behaviour of the cell.4. Histology and electron microscopy have indicated the presence of carbohydrate at the periphery of many mammalian cells. Some workers consider that such materials are present in a ‘cell coat’ covering the plasma membrane, rather than in the membrane itself.5. Studies on the isolation and characterization of membrane glycoproteins have indicated that small oligosaccharide units linked toO‐seryl or glutamyl residues in proteins are important structural units in plasma membranes.6. The glycosylation of proteins takes place within the membranes of the endo‐plasmic reticulum. Studies of glycoprotein biosynthesis suggest that the cell is able to synthesize a diversity of cell‐surface structures from a relatively small number of monosaccharides.7. Modification of the sialic acid‐containing glycoproteins of the plasma membrane affects the transport of materials in and out of cells. Glycoproteins are present in membranes other than the plasma membrane, and are therefore considered to be integral components of membranes; hence the designation ‘cell coat’, whilst useful as a descriptive term, should not be taken to indicate that glycoproteins are constituents of a functional entity separate from that of the membrane.8. Evidence that membrane glycoproteins may act as sites of interaction between cells is discussed. The involvement of glycoproteins in such a role would explain why the cell had developed a biosynthetic process capable of producing varied surface oligosaccharide structur

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1968.tb00964.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY