摘要:

Summary1. Plants contain growth regulators that are non‐hormonal in nature. These regulators change in concentration during ontogeny and when applied exogenously, can either stimulate or depress growth. While the bulk of either the phenolic or terpenoid regulators are localized within the vacuole, they can also be found within other cellular compartments where they may act upon metabolic pathways, modifying either cell multiplication or elongation.2. Non‐hormonal growth regulators may affect the synthesis and/or destruction of phytohormones, mainly indole‐3‐acetic acid (IAA). These regulators behave non‐specifically, modifying the actions of auxins, gibberellins and cytokinins upon growth.3. A variety of both uncertainties and unresolved contradictions exist that have prevented a thorough elucidation of the mechanisms of actions of both phenolic and terpenoid regulators. These uncertainties and unresolved contradictions include lack of data regarding compartmentalization of many of the inhibitors. This raises the question of whether their intracellular concentrations become elevated sufficiently to affect metabolic pathwaysin vivo.Exogenously applied regulators of non‐hormonal nature usually interfere with growth only at high concentrations. Therefore, the possibility cannot be excluded that under these conditions, reactions occur within the cell that are absentin vivo.4. The specific properties of natural non‐hormonal regulators are similar in certain respects to phytohormones. For example, both of them may be biogenetically bound within metabolic centres: shikimate (phenolics, indoles, alkaloids), bi‐benzi (coumarins) or acetate‐mevalonate (terpenoids, fluorens, sesquiterpenes, cytokinins). In addition, both non‐hormonal regulators and phytohormones exhibit biological activity in growth bioassays.5. Non‐hormonal regulators may possess a number of useful purposes, e.g. test substances such as fusicoccin permit the investigation of the mode of action of phytohormones, specific inhibitors blocking special forms of growth and protectors of phytohormon

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00708.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Summary(1) Based on data from the literature, the phenomenon of homing in salmonids is examined with special reference to the Atlantic salmon. Wild, native fish demonstrate an excellent homing ability, judged from percent return to the home river (1–3 %) and straying to non‐native watersheds (less than 3 % of returning fish).(2) The homing ability in wild fish is shown to be closely related to the existence of reproductively isolated populations between and within watersheds, as demonstrated by data from salmonid ecology and biochemical genetics.(3) Two main hypotheses have dominated the literature on salmonid homing during recent years: (a) An ‘imprinting’ hypothesis based on a process of learning of stream odours during seaward migration, coupled with sun‐orientation for open sea navigation, (b) A ‘pheromone’ hypothesis related to odours from fish and based on inheritance and the seasonal migrating schedules of discrete populations.(4) The olfactory sense has been demonstrated as mandatory for salmonids, both in near range and open sea navigation. According to genetic, sensory and ecological aspects of homing, the pheromone hypothesis is therefore concluded to be the most appropriate.(5) Fish produced from artificially fertilized eggs, released within native systems or transplanted, demonstrate a reduced homing ability. Since hatchery‐raised fish demonstrate a survival in sea equivalent to that of wild fish, a genetic disturbance of navigational ability has been suggested, resulting from the production of population hybrids by man.(6) Studies made in the fields of behaviour, electrophysiology and chemistry strongly suggest that population‐specific fish odours are involved in home‐stream recognition by salmonids.(7) An evaluation of ‘imprinting’ experiments related to artificial organic compounds reveals that: (a) the odorant properties of the applied chemicals must be questioned, (b) imprinting related to olfaction may be based on a weak theoretical foundation, (c) returns obtained in census experiments may be adequately explained through ecological interpretations, and (d) behavioural preferences obtained from exposure to non‐natural compounds may be founded on mechanisms not associated with homing.(8) A logical link between the use of olfaction and the role of genetics in salmonid homing is emphasized, together with its practical implication

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00709.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Summary1. Polyhedral bodies are present in several groups of autotrophic bacteria that assimilate inorganic carbon via the Calvin cycle, including members of the colourless sulphur‐ oxidizing bacteria, ammonia‐ and nitrite‐oxidizing bacteria and all cyanobacteria (blue‐green algae) examined. Other groups of Calvin‐cycle bacteria lack the inclusions, which have not been found in the purple photosynthetic bacteria, or in the hydrogen bacteria, with one exception in each case. Polyhedral bodies also occur in the chlorophyllb‐containing photosynthetic symbiotic prokaryote,Prochloron, and in several cyanelles. The inclusion bodies have not been found in prokaryotes that cannot fix carbon dioxide via the Calvin cycle, or in eukaryotes.2. Polyhedral bodies have been isolated from a colourless sulphur bacterium (Thiobacillus neapolitanus), two nitrifying bacteria (Nitrobacter agilisandNitrosomonassp.) and two cyanobacteria (Anabaena cylindricaandChlorogloeopsis fritschii). Ribulose 1,5‐bisphosphate carboxylase/oxygenase (RuBisCO), the carbon dioxide‐fixing enzyme of the Calvin cycle, has been found in the polyhedral bodies in each case, confirming that these inclusions in autotrophic bacteria be re‐termed carboxysomes.3. Knowledge of carboxysome composition has been constrained by difficulties in carboxysome isolation, although effective methods, including cell disruption in low‐ionic‐strength buffers followed by density‐gradient centrifugation through silicon polymers, or sucrose, followed be preparative agarose electrophoresis, are now available.4. Analysis of isolatedT. neapolitanus, N. agilisandC. fritschiicarboxysomes by dissociating sodium dodecyl sulphate‐polyacrylamide gel electrophoresis has revealed the presence of 7–15 polypeptides, the most abundant being the large and small subunits of RuBisCO. Two polypeptides of theT. neapolitanuscarboxysomes have been ascribed to the carboxysome membrane (shell), although the identity of other polypeptides is unknown.5. DNA of unknown function has been reported in carboxysomes isolated from twoNitrobacterspecies and may be present in the organelles fromT. neapolitanus.6. RuBisCO occurs in both the carboxysomes and in soluble form in the cytoplasm of carboxysome‐containing bacteria. Structural, kinetic, regulatory and immunological comparisons have demonstrated full or near identity between the cytoplasmic and carboxysomal forms of the enzyme. As with RuBisCO from chloroplasts and from almost all non‐carboxysome‐containing bacteria, the cytoplasmic and carboxysomal RuBisCOs each consist of eight large plus eight small subunits. All RuBisCOs are bifunctional enzymes, oxygen acting as a competitive inhibitor of carboxylation, and carbon dioxide acting competitively to inhibit the apparently wasteful oxygenase reaction. Carbon dioxide and oxygen fixation occur at the same site on the large subunit. Despite extensive study, the function of the small subunits is unknown. All RuBisCOs can exist in an inactive and active form, activation proceeding by an ordered reversible binding of carbon dioxide, followed by a divalent metal cation, to the large subunit, at sites distinct from the catalytic site. Identity of the activation and catalytic sites at lysine residues 201 and 175, respectively, on the RuBisCO large subunit in organisms as phylogenetically diverse as spinach andRhodospirillum rubrumsuggests a uniform mechanism of RuBisCO regulation throughout the Calvin cycle autotrophs.7. Carboxysome function is unknown, although several possibilities exist. A role for the organelles in autotrophy has been assumed and studies on carboxysome function have centred on relations between the organelles and RuBisCO. Carboxysomes may serve as active sites of carbon dioxide fixation, act as CO2‐concentrating compartments for RuBisCO, protect RuBisCO from adverse effects such as inhibition by oxygen and degradation by proteases, and/or act as general protein‐storage bodies. Evidence and argument for and against each of these possibilities is presented from whole‐cell and enzyme studies with sulphur bacteria and cyanobacteria, including specialist and nutritionally versatile strains.8. The need for further knowledge of carboxysome composition, particularly including the structure and properties of the protein shell, to permit further understandin

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Summary1. The species‐area curve has been studied now for more than one hundred years. In this time four hypotheses have been proposed to account for this pattern ‐ the Random Placement (or Passive Sampling) Hypothesis, the Habitat Diversity Hypothesis, the Equilibrium Theory (or Area Per Se Hypothesis), and the Disturbance Hypothesis. The Random Placement Hypothesis was the first of these and is the simplest, proposing that nothing other than a random placement of species and individuals over area is occurring. This should be considered the Null Hypothesis for species‐area studies and must be tested and rejected before any other hypothesis can be considered viable.2. The Habitat Diversity Hypothesis explains the species‐area curve via the addition of new habitats with increasing area. It is supposed to result in a Power Function curve. It has been invoked a number of times but has not yet been shown experimentally to give rise to a species‐area curve.3. The Equilibrium Theory proposes that species become extinct faster on small islands as a result of the lower population sizes on such islands. This is probably the hypothesis most frequently invoked to account for the species–area curve. It is also said to result in a species‐area curve of the Power Function form. Many of the tests of this hypothesis have, however, been inadequate and on only two occasions has the null hypothesis been tested.4. The Disturbance Hypothesis also proposes that species become extinct faster on small islands, but in this case it is supposed to occur because disturbances are more frequent and more intense on these islands. This hypothesis has only rarely been considered yet it is consistent with many of the observations used to support the Equilibrium Theory. Furthermore, it has been shown experimentally, in one situation at least, to give rise to a species‐area curve.5. Two methods exist by which the null hypothesis of Random Placement can be tested. One is based on probability calculations; the other on sampling in the field. Both methods have been successfully used to test the null hypothesis, and to demonstrate biologically interesting and meaningful patterns.6. The existence of a Power Function curve has been taken to indicate that the Equilibrium Theory is correct. Likewise, an Exponential curve has been taken by some as indicating that Random Placement is occurring. These views can be shown, theoretically and empirically, to be invalid. The fitting of a particular type of curve does not test any of the hypotheses described.7. Species‐area curves can be meaningfully used to measure the relative species diversity of a community, and biologically interesting patterns can be found by comparing communities in this way.8. More intensive studies, testing the null hypothesis and performing manipulative experiments, are necessary if the processes underlying the species–area curve a

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00711.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1984.tb00712.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY