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The '''heterokonts''' |
The terms '''heterokonts''' and '''stramenopiles''' refer to overlapping clusters of [[eukaryote]]s<ref name="urlstramenopiles">{{cite web |url=http://www.uniprot.org/taxonomy/33634 |title=stramenopiles |format= |work= |accessdate=2009-03-08}}</ref> currently containing more than 100,000 known species.<ref name="Hoek">{{cite book | last=Hoek | first=C. van den | coauthors=D. G. Mann; H. M. Jahns | year=1995 | pages=104, 124, 134, 166 |
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| title=Algae: An Introduction to Phycology | location=Cambridge | publisher=Cambridge University Press | isbn=0-521-31687-1 }}</ref> |
| title=Algae: An Introduction to Phycology | location=Cambridge | publisher=Cambridge University Press | isbn=0-521-31687-1 }}</ref> The term 'hHeterokont' has a much longer history and has been used to refer to various groupings of algae. Stramenopiles was introduced more recently to refer to a monophyletic and holophyletic lineage defined by the presence of distinctive three-part hairs on the flagella (or derived therefrom). All heterokonts and many stramenopiles are [[algae]], ranging from the giant multicellular [[kelp]] to the unicellular [[diatom]]s, which are a primary component of [[plankton]]. Some non-algal stramenopiles are the opalines, actinophryid heliozoa, various heterotrophic flagellates, the (generally [[parasitic]]) [[oomycete]]s, including ''[[Phytophthora]]'' of [[Irish potato famine]] infamy and ''[[Pythium]]'' which causes seed rot and damping off. |
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The name '''heterokonts''' refers to the |
The name '''heterokonts''' refers to the occurrence of different flagella in the motile (flagellated) life cycle stage of algae. |
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==Chloroplasts== |
==Chloroplasts== |
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Heterokont algae are [[chromista|chromists]] |
Heterokont algae are placed by some in the polyphyletic [[chromista|chromists]] most of which have[[chloroplast]]s surrounded by four membranes, which are counted from the outermost to the innermost membrane. The first membrane is continuous with the host's [[Endoplasmic reticulum|chloroplast endoplasmic reticulum]], or cER. The second membrane presents a barrier between the lumen of the endoplasmic reticulum and the primary endosymbiont or [[chloroplast]], which represents the next two membranes, within which the thylakoid membranes are found. This arrangement of membranes suggest that heterokont chloroplasts were obtained from the reduction of a symbiotic [[red algae|red algal]] eukaryote, which had arisen by evolutionary divergence from the monophyletic primary endosymbiotic ancestor that is thought to have given rise to all eukaryotic [[photoautotrophs]]. The chloroplasts characteristically contain [[chlorophyll a]] and [[chlorophyll c]], and usually the accessory pigment [[fucoxanthin]], giving them a golden-brown or brownish-green color. |
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Most basal heterokonts are colorless. This suggests that they diverged before the acquisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the [[haptophyte]]s. |
Most basal heterokonts are colorless. This suggests that they diverged before the acquisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the [[haptophyte]]s which are placed by some in the [[chromista|chromists]]. The similarity in plastids has led some to argue that heterokont algae, [[cryptomonad]]s and haptophytes have a common [[phylogeny|phylogenetic]]. This may be interpreted as suggesting that the ancestral heterokont was an alga, and all colorless groups arose through loss of the secondary endosymbiont and its chloroplast. Others point to the likelihood of the same plastids being acquired by different lineages, the significant cytological differences among these three types of organism, and that molecular analysis of evolutionary relationships do not confirm a close relationship. They conclude that the [[chromista|chromists]] are polyphyletic. |
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==Motile cells== |
==Motile cells== |
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Many heterokonts are unicellular [[flagellate]]s, and most others produce flagellate cells at some point in their life-cycle, for instance as [[gamete]]s or [[zoospore]]s. The name heterokont |
Many heterokonts are unicellular [[flagellate]]s, and most others produce flagellate cells at some point in their life-cycle, for instance as [[gamete]]s or [[zoospore]]s. The name heterokont has come to refer to the characteristic presence of two unequal (dissimilar) flagella. The anterior or ''tinsel'' flagellum is covered with lateral bristles or ''[[mastigonemes]]'', while the other flagellum is whiplike, smooth, and usually shorter, or sometimes reduced to a basal body. The flagella are inserted subapically or laterally, and are usually supported by four [[microtubule]] roots in a distinctive pattern. |
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Mastigonemes are manufactured from [[glycoprotein]]s in the cell's [[endoplasmic reticulum]] before being transported to the anterior flagella's surface. When the tinsel flagellum moves, the mastigonemes create a retrograde current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the heterokonts, thereby including a few protists that do not produce cells with the typical heterokont form. Mastigonemes have been lost in a few heterkont lines, most notably the diatoms. |
Mastigonemes are manufactured from [[glycoprotein]]s in the cell's [[endoplasmic reticulum]] before being transported to the anterior flagella's surface. When the tinsel flagellum moves, the mastigonemes create a retrograde current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the heterokonts, thereby including a few protists that do not produce cells with the typical heterokont form. Mastigonemes have been lost in a few heterkont lines, most notably the diatoms. |
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==Classification== |
==Classification== |
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As noted above, classification varies considerably. Originally the |
As noted above, classification varies considerably. Originally the term Heterokontae was introduced for xanthophyte plus raphidophyte algae by Luther in 1899. It has undergone numerous changes, and for some points to a division within the kingdom Plantae and others see it as a group of Protista: |
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Division Chrysophyta |
Division Chrysophyta |
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Division Phaeophyta ([[brown alga]]e) |
Division Phaeophyta ([[brown alga]]e) |
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In this scheme, however, the Chrysophyceae are [[paraphyletic]] to both other groups. As a result, various members have been given their own classes and often divisions. |
In this scheme, however, the Chrysophyceae are [[paraphyletic]] to both other groups. As a result, various members have been given their own classes and often divisions. Some recent systems often treat these as classes within a single division, called the Heterokontophyta, Chromophyta, or Ochrophyta. This is not universal, however: Round ''et al.'' treat the diatoms as a division. |
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The discovery that [[oomycete]]s and [[hyphochytrid]]s are related to these algae, rather than fungi, as previously thought, has led many authors to include these two groups among the heterokonts. Should it turn out that they evolved from colored ancestors, the heterokont group would be paraphyletic in their absence. Once again, however, usage varies. [[David J. Patterson]] named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, [[mitochondrion|mitochondria]] with tubular [[crista]]e, and open [[mitosis]]. He used the stramenopiles as |
The discovery that [[oomycete]]s and [[hyphochytrid]]s are related to these algae, rather than fungi, as previously thought, has led many authors to include these two groups among the heterokonts. Should it turn out that they evolved from colored ancestors, the heterokont group would be paraphyletic in their absence. Once again, however, usage varies. [[David J. Patterson]] named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, [[mitochondrion|mitochondria]] with tubular [[crista]]e, and open [[mitosis]]. He used the stramenopiles as an example of a phylogenetically driven classification without the need for Linnaean ranks. This concept has remained more stable than that of heterokonts, but their use within other ranked systems varies. |
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[[Thomas Cavalier-Smith]] treats the heterokonts as identical in composition with the stramenopiles |
[[Thomas Cavalier-Smith]] treats the heterokonts as identical in composition with the stramenopiles. He has proposed placing them in a separate kingdom [[Chromalveolata]], together with the haptophytes, cryptomonads and alveolates. This is one of the most common revisions to the [[kingdom (biology)|five-kingdom system]], but has not been generally adopted, partly because some biologists point to the evidence against their monophyly. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila. |
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Some sources divide the heterokonts into the [[autotrophic]] [[Ochrophyta]] and [[heterotrophic]] [[Bigyra]] and [[Pseudofungi]].<ref name="pmid19213601">{{cite journal |author=Riisberg I, Orr RJ, Kluge R, ''et al.'' |title=Seven gene phylogeny of heterokonts |journal=Protist |volume=160 |issue=2 |pages=191–204 |year=2009 |month=May |pmid=19213601 |doi=10.1016/j.protis.2008.11.004 |url=http://linkinghub.elsevier.com/retrieve/pii/S1434-4610(08)00075-8}}</ref> However, some modifications to these classifications have been suggested. |
Some sources divide the heterokonts into the [[autotrophic]] [[Ochrophyta]] and [[heterotrophic]] [[Bigyra]] and [[Pseudofungi]].<ref name="pmid19213601">{{cite journal |author=Riisberg I, Orr RJ, Kluge R, ''et al.'' |title=Seven gene phylogeny of heterokonts |journal=Protist |volume=160 |issue=2 |pages=191–204 |year=2009 |month=May |pmid=19213601 |doi=10.1016/j.protis.2008.11.004 |url=http://linkinghub.elsevier.com/retrieve/pii/S1434-4610(08)00075-8}}</ref> However, some modifications to these classifications have been suggested. |
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==Rationale for "stramenopile"== |
==Rationale for "stramenopile"== |
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⚫ | The term stramenopile was introduced to improve on the use of 'heterokont' and offer an unambiguous and stable definition by pointing to the synapomorphy for the group. This approach defines a monophyletic and holophyletic taxon that includes all descendants of the common ancestor. This makes a break from the previously variable interpretation of 'heterokont' - and one which is often restricted to the plastic members of the group (http://www.amjbot.org/content/91/10/1508.full.pdf). "Stramen' is the latin name for straw, a noun used in apposition with "pilus' for hair, and referring to the central tubular part of the hairs that are attached to the flagellar or body surface. Adl and coauthors say: <blockquote>Regarding the spelling of stramenopile, it was originally spelled '''stramenopile'''. The Latin word for ‘‘straw’’ is stramine-us, -a, -um, adj. [stramen], made of straw—thus, it should have been spelled '''straminopile'''. However, Patterson (1989)<ref name="pmid10527921">{{cite journal |author=Patterson DJ |title=The Diversity of Eukaryotes |journal=Am. Nat. |volume=154 |issue=S4 |pages=S96–S124 |year=1999 |month=October |pmid=10527921 |doi=10.1086/303287 |url=http://www.journals.uchicago.edu/cgi-bin/resolve?AN991002}}</ref> clearly stated that this is a common name (hence, lower case, not capitalized) and, as a common name, it can be spelled as Patterson chooses. If he had stipulated that the name was a formal name, governed by rules of nomenclature, then his spelling would have been an orthogonal mutation and one would simply correct the spelling in subsequent publications (e.g. Straminopiles). But, it was not Patterson’s desire to use the term in a formal sense. Thus, if we use it in a formal sense, it must be formally described (and in addition, in Latin, if it is to be used botanically). However, and here is the strange part of this, many people liked the name, but wanted it to be used formally. So they capitalized the first letter, and made it Stramenopiles; others corrected the Latin spelling to Straminopiles.<ref name="pmid16248873">{{cite journal |author=Adl SM, Simpson AG, Farmer MA, ''et al.'' |title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists |journal=J. Eukaryot. Microbiol. |volume=52 |issue=5 |pages=399–451 |year=2005 |pmid=16248873 |doi=10.1111/j.1550-7408.2005.00053.x}}</ref></blockquote> |
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The origin of the name stramenopile is explained by Adl and coauthors: |
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⚫ | <blockquote>Regarding the spelling of stramenopile, it was originally spelled '''stramenopile'''. The Latin word for ‘‘straw’’ is stramine-us, -a, -um, adj. [stramen], made of straw—thus, it should have been spelled '''straminopile'''. However, Patterson (1989)<ref name="pmid10527921">{{cite journal |author=Patterson DJ |title=The Diversity of Eukaryotes |journal=Am. Nat. |volume=154 |issue=S4 |pages=S96–S124 |year=1999 |month=October |pmid=10527921 |doi=10.1086/303287 |url=http://www.journals.uchicago.edu/cgi-bin/resolve?AN991002}}</ref> clearly stated that this is a common name (hence, lower case, not capitalized) and, as a common name, it can be spelled as Patterson chooses. If he had stipulated that the name was a formal name, governed by rules of nomenclature, then his spelling would have been an orthogonal mutation and one would simply correct the spelling in subsequent publications (e.g. Straminopiles). But, it was not Patterson’s desire to use the term in a formal sense. Thus, if we use it in a formal sense, it must be formally described (and in addition, in Latin, if it is to be used botanically). However, and here is the strange part of this, many people liked the name, but wanted it to be used formally. So they capitalized the first letter, and made it Stramenopiles; others corrected the Latin spelling to Straminopiles.<ref name="pmid16248873">{{cite journal |author=Adl SM, Simpson AG, Farmer MA, ''et al.'' |title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists |journal=J. Eukaryot. Microbiol. |volume=52 |issue=5 |pages=399–451 |year=2005 |pmid=16248873 |doi=10.1111/j.1550-7408.2005.00053.x}}</ref></blockquote> |
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==References== |
==References== |
Revision as of 05:35, 31 December 2012
Heterokonts | |
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Pacific rockweed, Fucus distichus, in Olympic National Park | |
Scientific classification | |
Domain: | |
Kingdom: | |
Phylum: | Heterokontophyta
|
Typical classes | |
|
The terms heterokonts and stramenopiles refer to overlapping clusters of eukaryotes[1] currently containing more than 100,000 known species.[2] The term 'hHeterokont' has a much longer history and has been used to refer to various groupings of algae. Stramenopiles was introduced more recently to refer to a monophyletic and holophyletic lineage defined by the presence of distinctive three-part hairs on the flagella (or derived therefrom). All heterokonts and many stramenopiles are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton. Some non-algal stramenopiles are the opalines, actinophryid heliozoa, various heterotrophic flagellates, the (generally parasitic) oomycetes, including Phytophthora of Irish potato famine infamy and Pythium which causes seed rot and damping off.
The name heterokonts refers to the occurrence of different flagella in the motile (flagellated) life cycle stage of algae.
Chloroplasts
Heterokont algae are placed by some in the polyphyletic chromists most of which havechloroplasts surrounded by four membranes, which are counted from the outermost to the innermost membrane. The first membrane is continuous with the host's chloroplast endoplasmic reticulum, or cER. The second membrane presents a barrier between the lumen of the endoplasmic reticulum and the primary endosymbiont or chloroplast, which represents the next two membranes, within which the thylakoid membranes are found. This arrangement of membranes suggest that heterokont chloroplasts were obtained from the reduction of a symbiotic red algal eukaryote, which had arisen by evolutionary divergence from the monophyletic primary endosymbiotic ancestor that is thought to have given rise to all eukaryotic photoautotrophs. The chloroplasts characteristically contain chlorophyll a and chlorophyll c, and usually the accessory pigment fucoxanthin, giving them a golden-brown or brownish-green color.
Most basal heterokonts are colorless. This suggests that they diverged before the acquisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the haptophytes which are placed by some in the chromists. The similarity in plastids has led some to argue that heterokont algae, cryptomonads and haptophytes have a common phylogenetic. This may be interpreted as suggesting that the ancestral heterokont was an alga, and all colorless groups arose through loss of the secondary endosymbiont and its chloroplast. Others point to the likelihood of the same plastids being acquired by different lineages, the significant cytological differences among these three types of organism, and that molecular analysis of evolutionary relationships do not confirm a close relationship. They conclude that the chromists are polyphyletic.
Motile cells
Many heterokonts are unicellular flagellates, and most others produce flagellate cells at some point in their life-cycle, for instance as gametes or zoospores. The name heterokont has come to refer to the characteristic presence of two unequal (dissimilar) flagella. The anterior or tinsel flagellum is covered with lateral bristles or mastigonemes, while the other flagellum is whiplike, smooth, and usually shorter, or sometimes reduced to a basal body. The flagella are inserted subapically or laterally, and are usually supported by four microtubule roots in a distinctive pattern.
Mastigonemes are manufactured from glycoproteins in the cell's endoplasmic reticulum before being transported to the anterior flagella's surface. When the tinsel flagellum moves, the mastigonemes create a retrograde current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the heterokonts, thereby including a few protists that do not produce cells with the typical heterokont form. Mastigonemes have been lost in a few heterkont lines, most notably the diatoms.
Classification
As noted above, classification varies considerably. Originally the term Heterokontae was introduced for xanthophyte plus raphidophyte algae by Luther in 1899. It has undergone numerous changes, and for some points to a division within the kingdom Plantae and others see it as a group of Protista:
Division Chrysophyta
- Class Chrysophyceae (golden algae)
- Class Bacillariophyceae (diatoms)
Division Phaeophyta (brown algae)
In this scheme, however, the Chrysophyceae are paraphyletic to both other groups. As a result, various members have been given their own classes and often divisions. Some recent systems often treat these as classes within a single division, called the Heterokontophyta, Chromophyta, or Ochrophyta. This is not universal, however: Round et al. treat the diatoms as a division.
The discovery that oomycetes and hyphochytrids are related to these algae, rather than fungi, as previously thought, has led many authors to include these two groups among the heterokonts. Should it turn out that they evolved from colored ancestors, the heterokont group would be paraphyletic in their absence. Once again, however, usage varies. David J. Patterson named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, mitochondria with tubular cristae, and open mitosis. He used the stramenopiles as an example of a phylogenetically driven classification without the need for Linnaean ranks. This concept has remained more stable than that of heterokonts, but their use within other ranked systems varies.
Thomas Cavalier-Smith treats the heterokonts as identical in composition with the stramenopiles. He has proposed placing them in a separate kingdom Chromalveolata, together with the haptophytes, cryptomonads and alveolates. This is one of the most common revisions to the five-kingdom system, but has not been generally adopted, partly because some biologists point to the evidence against their monophyly. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila.
Some sources divide the heterokonts into the autotrophic Ochrophyta and heterotrophic Bigyra and Pseudofungi.[3] However, some modifications to these classifications have been suggested.
Rationale for "stramenopile"
The term stramenopile was introduced to improve on the use of 'heterokont' and offer an unambiguous and stable definition by pointing to the synapomorphy for the group. This approach defines a monophyletic and holophyletic taxon that includes all descendants of the common ancestor. This makes a break from the previously variable interpretation of 'heterokont' - and one which is often restricted to the plastic members of the group (http://www.amjbot.org/content/91/10/1508.full.pdf). "Stramen' is the latin name for straw, a noun used in apposition with "pilus' for hair, and referring to the central tubular part of the hairs that are attached to the flagellar or body surface. Adl and coauthors say:
Regarding the spelling of stramenopile, it was originally spelled stramenopile. The Latin word for ‘‘straw’’ is stramine-us, -a, -um, adj. [stramen], made of straw—thus, it should have been spelled straminopile. However, Patterson (1989)[4] clearly stated that this is a common name (hence, lower case, not capitalized) and, as a common name, it can be spelled as Patterson chooses. If he had stipulated that the name was a formal name, governed by rules of nomenclature, then his spelling would have been an orthogonal mutation and one would simply correct the spelling in subsequent publications (e.g. Straminopiles). But, it was not Patterson’s desire to use the term in a formal sense. Thus, if we use it in a formal sense, it must be formally described (and in addition, in Latin, if it is to be used botanically). However, and here is the strange part of this, many people liked the name, but wanted it to be used formally. So they capitalized the first letter, and made it Stramenopiles; others corrected the Latin spelling to Straminopiles.[5]
References
- ^ "stramenopiles". Retrieved 2009-03-08.
- ^ Hoek, C. van den (1995). Algae: An Introduction to Phycology. Cambridge: Cambridge University Press. pp. 104, 124, 134, 166. ISBN 0-521-31687-1.
{{cite book}}
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ignored (|author=
suggested) (help) - ^ Riisberg I, Orr RJ, Kluge R; et al. (2009). "Seven gene phylogeny of heterokonts". Protist. 160 (2): 191–204. doi:10.1016/j.protis.2008.11.004. PMID 19213601.
{{cite journal}}
: Explicit use of et al. in:|author=
(help); Unknown parameter|month=
ignored (help)CS1 maint: multiple names: authors list (link) - ^ Patterson DJ (1999). "The Diversity of Eukaryotes". Am. Nat. 154 (S4): S96–S124. doi:10.1086/303287. PMID 10527921.
{{cite journal}}
: Unknown parameter|month=
ignored (help) - ^ Adl SM, Simpson AG, Farmer MA; et al. (2005). "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists". J. Eukaryot. Microbiol. 52 (5): 399–451. doi:10.1111/j.1550-7408.2005.00053.x. PMID 16248873.
{{cite journal}}
: Explicit use of et al. in:|author=
(help)CS1 maint: multiple names: authors list (link)