摘要:

Summary of SymposiumThe following papers and abstracts represent a symposium held on 11 August 1973 at the First International Congress of Systematic and Evolutionary Biology (ICSEB), Boulder, Colorado:Introduction, by LynnMargulisI. Evolutionary significance of cell division phenomena in Protistsa. Nonphotosynthetic Protists, by KarlGrellb. Photosynthetic Protists, by JeremyPickett‐HeapsII. Implications and extensions of the serial endosymbiosis theory of the origin of eukaryotes, by F. J. R. TaylorIII. Two billion years of prokaryotic cells and the emergence of eukaryotes, by ElsoS. BarghoornIV. How many are the kingdoms of organisms?, by GordonF. Leedale

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02806.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

AbstractIn my opinion, the problem of accounting for the origin of eucaryotic cells cannot be dissociated from the problem of accounting for the origin of mitosis. A primeval cell type could not become eucaryotic unless it had concurrently evolved a method for reliably partitioning its genetic material.Modern procaryotes perhaps had their genetic material attached to the cell membrane: partitioning may be accomplished by growth of the membrane between attachment points. The only possibly similar mechanism of chromosome separation so far described in eucaryotic cells may be in the dinoflagellates.

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02808.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryIn comparison to other theories put forward so far, the Serial Endosymbiosis Theory appears to be the most critically favoured as an explanation for the origin of mitochondria and chloroplasts. For this reason some of its implications are drawn attention to. In particular it is shown that present hierarchical concepts and terminology based on the classical cell theory are inadequate to cope with the S.E.T. (as the theory is abbreviated here). It is shown that the topological relations of mitochondria and chloroplasts to the cell suggest that they are topologically “outside” it, “embraced” rather than lying truly within it. This position is consistent with the S.E.T. On the other hand microtubule‐organising‐centres are truly within the cell. An autogenous origin for the latter seems to be more likely than the endosymbiotic proposal of Margulis.In addition to the primary origin of organelles by the transformation of entire prokaryotic endosymbionts, the possibility of the maintenance of eukaryotic organelles produced by one cell, taken into another, is discussed. Examples of some recently discovered, unusual photosynthetic states in ciliates, brought about by temporary foreign chloroplast maintenance, and possibly degeneration of endosymbiotic photosynthetic flagellates, are discussed in this context. The existence of some contemporary examples of photosynthetic bodies which seem to be intermediate between endosymbiotic blue‐green algae and chloroplasts, suggests that some organelles may have had a more recent origin than the Precambrian Era, the process being a continuous one.Some of the difficulties inherent in alternative theories for the origin of eukaryotes are discussed. It is stressed that alternative proposals have not yet received intensive exposition and comparisons with the S.E.T. are thus difficult. Attempts to use single criteria (particularly biochemical) as phylogenetic “markers” should be made with due consideration of the S.E.T.Finally, it has bearing on the recognition of kingdoms, for it widens the already acknowledged chasm between prokaryotes and eukaryotes, intermediates between the two types of organisation being impossible (as stressed by Margulis).

ISSN:0040-0262    

DOI:10.2307/1218702

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

AbstractA brief resumé will be made of the earliest evidence of cells and cellular organization from carbonaceous sediments of the early Precambrian of South Africa and Rhodesia.It is proposed to make a brief synopsis of the general level of morphological organization by the middle of Precambrian time at about the midpoint in the history of the earth, centering the discussion on the microbiota of the Gunflint chert as an example of a “benchmark” in the level of evolution of life at approximately 2 times 109years ago.With the assumption that the Gunflint biota is composed solely of prokaryotic organisms it is of interest to examine subsequent Precambrian fossil assemblages with a view to evaluating critically the evidence presented in recent years for the appearance of eukaryotic organisms in the late Precambrian. In this connection, various aspects of cell clumping, lysis and laboratory controlled silicification of blue‐green algal cells will be considered.

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02810.x

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02811.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe division of living organisms into Plantae and Animalia fails to recognise the major evolutionary discontinuity between prokaryotes and eukaryotes. In addition, fungi and “plant‐animal” unicells lie uncomfortably in such a two‐kingdom system. Systems have been proposed which separate prokaryotes from eukaryotes and divide the latter into several kingdoms. These schemes share two limitations. The “low” eukaryote kingdom (Protoctista or Protista) contains phyla more closely related to phyla of the “higher” kingdoms than to other phyla in the same kingdom. Secondly, the higher kingdoms are polyphyletic to a disturbing degree.Can one make broad classifications without these limitations? A Prokaryota/Eukaryota two‐kingdom scheme is one possibility; another is a four‐kingdom scheme in which the protistan level is absorbed into the eukaryote kingdoms; a third possibility is a system in which phylum and phylogeny units stand as monophyletic kingdoms; such a multikingdom scheme provides fruitful scope for discussion. The Prokaryota/Eukaryota and multikingdom schemes allow flexibility for incorporation of new information on relationships, but may be thought too fragmentary for practical taxonomy. If so, various four‐ or five‐kingdom schemes are available.

ISSN:0040-0262    

DOI:10.2307/1218705

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe method of the “multiple working hypothesis” is best applied to “those subjects in which, while much is known, more remains to be known,” a description which certainly is applicable to the Phylogeny of the Protista. Although various proposed phylogenies have been stoutly defended by their authors as unassailable, each has been based on one or another line of evidence, generalization or previous assumption which is contested strongly by others.Previous workers have regarded the Protista as animals or as plants, as one distinct kingdom, or as including representatives of two, three or as many as 13 kingdoms. Classifications and phylogenetic interpretations have been based on various aspects of morphology, cytology, ultrastructure, biochemistry, physiology, life cycles, or the fossil record. Each resulting classification has much supporting evidence but leaves unanswered other vexing problems.The present symposium includes only a sampling of the types of approach currently being used, but may aid in stimulating additional interest and study of the highly diverse and intriguing organisms known as the Protista.

ISSN:0040-0262    

DOI:10.2307/1218706

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryEven though the fossil record is incomplete and perhaps difficult to use in phylogenetic studies of the Protista, in the last resort it is the true basis for any real phylogeny as the dimension of time must be taken into consideration. Other hypothetical phylogenies represent speculation based on analysis of a single time plane. Major algal differentiation was a series of ancient events that took place early in the Precambrian and preceded the diversification of the animal kingdom. Every plant division, five of the classes and seven orders of plants, are represented by fossils of Precambrian age. In addition over 1500 described cyst species of some algal group (= Hystrichophyta or Acritarcha) occur in the Precambrian and Paleozoic, that may eventually fill in some of the gaps in the fossil record of the algae and contribute to a refinement of any future phylogenetic studies. With the increasing cooperation developing today between modern biologists and paleontologists interested in phylogenetic studies, I am optimistic for the future of this interesting and highly speculative field.

ISSN:0040-0262    

DOI:10.2307/1218707

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryWe first list the main experimental methods used to get an insight into the phylogenetic relationships of the presently existing bacterial genera. Their scope and relative merits are briefly discussed.As a model system we briefly summarize the application of most of those methods to elucidate the phylogenetic relationships within the genusAgrobacterium. The evolutionary development of this genus is described.Similar experiments withZymomonasare summarized.

ISSN:0040-0262    

DOI:10.2307/1218708

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe basis for, and advantages of, the use of sequence analysis of proteins are presented. Cytochrome c is used as an example and it is suggested that not enough work has been. done upon the amino acid sequences of proteins of fungi, especially cytochromec. Other means of studying proteins and enzymes in order to acquire data useful to evolutionists who deal with fungi are discussed, including analysis of mechanisms of control of enzyme activity, electrophoretic migration and properties of enzymes such as response to activators and inhibitors, pH and temperature optima etc. Finally, micromolecules are discussed in the context of their function in the fungi, and suggestions are made as to their present and potential use in phylogenetic studies of these organisms.

ISSN:0040-0262    

DOI:10.2307/1218709

出版商:Wiley    

年代:2019

数据来源: WILEY