|
The Archaeplastida (or Plantae ''sensu lato'' - in the broad sense) are a major group of eukaryotes, comprising the red algae (Rhodophyta), the green algae and the land plants, together with a small group of freshwater unicellular algae called glaucophytes. The chloroplasts of all these organisms are surrounded by two membranes, suggesting they developed directly from endosymbiotic cyanobacteria. In all other groups besides the amoeboid ''Paulinella chromatophora'', the chloroplasts are surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae. Although many studies have suggested that the Archaeplastida form a monophyletic group, a 2009 paper argues that they are in fact paraphyletic. The enrichment of novel red algal genes in a recent study demonstrates a strong signal for Plantae (Archaeplastida) monophyly and an equally strong signal of gene sharing history between the red/green algae and other lineages. This study provides insight on how rich mesophilic red algal gene data is crucial for testing controversial issues in eukaryote evolution and for understanding the complex patterns of gene inheritance in protists. The cells of the Archaeplastida typically lack centrioles and have mitochondria with flat cristae. There is usually a cell wall including cellulose, and food is stored in the form of starch. However, these characteristics are also shared with other eukaryotes. The main evidence that the Archaeplastida form a monophyletic group comes from genetic studies, which indicate that their plastids probably had a single origin. This evidence is disputed. Based on results to date, it is neither possible to confirm nor refute alternative evolutionary scenarios to a single primary endosymbiosis.〔Mackiewicz, P., & Gagat, P. (2014). Monophyly of Archaeplastida supergroup and relationships among its lineages in the light of phylogenetic and phylogenomic studies. Are we close to a consensus?. ''Acta Societatis Botanicorum Poloniae'', 83(4), 263-280.〕 Photosynthetic organisms with plastids of different origin (like brown algae, for instance) do not belong to Archaeplastida. The archaeplastidans fall into two main evolutionary lines. The red algae are pigmented with chlorophyll ''a'' and phycobiliproteins, like most cyanobacteria. The green algae and land plants – together known as Viridiplantae (Latin for "green plants") or Chloroplastida – are pigmented with chlorophylls ''a'' and ''b'', but lack phycobiliproteins. The glaucophytes have typical cyanobacterial pigments, and are unusual in retaining a cell wall within their plastids (called cyanelles). Archaeplastida should not be confused with the older and obsolete name Archiplastideae, which refers to cyanobacteria and other groups of bacteria.〔Copeland, H. F. (1956). ''The Classification of Lower Organisms''. Palo Alto: Pacific Books, p. 29, ().〕〔Bessey, C. E. (1907). "(A Synopsis of Plant Phyla )". ''Univ. Nebraska Studies'' 7: 275–358.〕 ==Taxonomy== The consensus in 2005, when the group consisting of the glaucophytes, red and green algae and land plants was named 'Archaeplastida',〔 was that it was a clade, i.e. was monophyletic. Many studies published since this date have provided evidence which is in agreement. On the other hand, other studies have suggested that the group is paraphyletic.〔〔 To date, the situation appears unresolved, but a strong signal for Plantae (Archaeplastida) monophyly has been demonstrated in a recent study (with an enrichment of red algal genes).〔 The assumption made here is that Archaeplastida is a valid clade. Various names have been given to the group. Some authors have simply referred to the group as plants or Plantae. However, the name Plantae is ambiguous, since it has also been applied to less inclusive clades, such as Viridiplantae and embryophytes. To distinguish, the larger group is sometimes known as Plantae ''sensu lato'' ("plants in the broad sense"). To avoid ambiguity, other names have been proposed. Primoplantae, which appeared in 2004, seems to be the first new name suggested for this group. Another name that has been applied to this node is Plastida, defined as the clade sharing "plastids of primary (direct prokaryote) origin () in ''Magnolia virginiana'' Linnaeus 1753". The name Archaeplastida was proposed in 2005 by a large international group of authors (Adl ''et al.'') who aimed to produce a classification for the eukaryotes which took into account morphology, biochemistry and phylogenetics, and which had "some stability in the near term." They rejected the use of formal taxonomic ranks in favour of a hierarchical arrangement where the clade names do not signify rank. Thus the phylum name 'Glaucophyta' and the class name 'Rhodophyceae' appear at the same level in their classification. The divisions proposed for the Archaeplastida are shown below in both tabular and diagrammatic form.〔 Archaeplastida: * Glaucophyta Skuja, 1954 (Glaucocystophyta Kies & Kremer, 1986) – glaucophytes ::Glaucophytes are a small group of freshwater single-celled algae. Their chloroplasts, called ''cyanelles'', have a peptidoglycan layer, making them more similar to cyanobacteria than those of the remaining Archaeplastida. * Rhodophyceae Thuret, 1855, emend. Rabenhorst, 1863, emend. Adl ''et al.'', 2005 (Rhodophyta Wettstein 1901) – red algae ::Red algae form one of the largest groups of algae. Most are seaweeds, being multicellular and marine. Their red colour comes from phycobiliproteins, used as accessory pigments in light capture for photosynthesis. * Chloroplastida Adl ''et al.'', 2005 (Viridiplantae Cavalier-Smith 1981; Chlorobionta Jeffrey 1982, emend. Bremer 1985, emend. Lewis and McCourt 2004; Chlorobiota Kendrick and Crane 1997) ::Chloroplastida is the term chosen by Adl ''et al.'' for the group made up of the green algae and land plants (embryophytes). Except where lost secondarily, all have chloroplasts without a peptidoglycan layer and lack phycobiliproteins. * * Chlorophyta Pascher, 1914, emend. Lewis & McCourt, 2004 – green algae (part) :::Adl et al. employ a narrow definition of the Chlorophyta; other sources include the Chlorodendrales and Prasinophytae, which may themselves be combined. : * * Ulvophyceae Mattox & Stewart, 1984 : * * Trebouxiophyceae Friedl, 1995 (Pleurastrophyceae Mattox et al. 1984; Microthamniales Melkonian 1990) : * * Chlorophyceae Christensen, 1994 * * Chlorodendrales Fritsch, 1917 – green algae (part) * * Prasinophytae Cavalier-Smith, 1998, emend. Lewis & McCourt, 2004 – green algae (part) * * ''Mesostigma'' Lauterborn, 1894, emend. McCourt ''in'' Adl ''et al.'', 2005 (Mesostigmata Turmel, Otis, and Lemieux 2002) * * Charophyta Karol ''et al.'', 2001, emend. Lewis & McCourt, 2004 (Charophyceae Smith 1938, emend. Mattox and Stewart 1984) – green algae (part) and land plants :::Charophyta ''sensu lato'', as used by Adl ''et al.'', is a monophyletic group which is made up of some green algae, including the stoneworts (Charophyta ''sensu stricto''), as well as the land plants (embryophytes). : * * Sub-divisions other than Streptophytina (below) were not given by Adl et al. ::::Other sources would include the green algal groups Chlorokybales, Klebsormidiales, Zygnematales and Coleochaetales. : * * Streptophytina Lewis & McCourt, 2004 – stoneworts and land plants * * * * Charales Lindley 1836 (Charophytae Engler, 1887) – stoneworts * * * * Plantae Haeckel 1866 (Cormophyta Endlicher, 1836; Embryophyta Endlicher, 1836, emend. Lewis & McCourt, 2004) – land plants (embryophytes) |2=Chlorodendrales |3=Prasinophytae |4=Mesostigma |5= }} }} }} }} }} }} 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Archaeplastida」の詳細全文を読む スポンサード リンク
|