Archaeplastida
Archaeplastida is a supergroup of eukaryotes that includes red algae, green algae, and land plants. It is characterized by the presence of chloroplasts derived from a primary endosymbiotic event involving a cyanobacterial ancestor. This group is significant in the evolutionary history of photosynthetic organisms and has had a major impact on the Earth's ecosystems.
7 Key excerpts on "Archaeplastida"
eBook - ePub- Arun Kumar, Jay Shankar Singh(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
...2008; Achibald 2009). Then a later subsequent endosymbiotic incident invoking the integration of eukaryotic algae into other eukaryotes, led to the development of all other plastids; that existed in Chromalveolata (kelps, dinoflagellates and malaria parasites), Excavata (euglenids) and Rhizaria (chlorarachniophytes) (Archibald 2012, Ball et al. 2011). The super group Archaeaplastida comprises only of the organisms with primary plastids, while secondary and tertiary plastids primarily exist in the members of the Chromalveolata (Cryptophyta, Stramenopiles, Haptophyta, Apicomplexa, Chromerida and certain Dinoflagellata), Excavata (Eugleonophyta) and Rhizaria (Chlorarachniophyta) (Fig. 1.2). The presence of plastid-lacking organisms is more surprising and confusing, it could be possible they never had plastids or lost their plastids. Based on the recent phylogenetic analyses on the host level, the group Stramenopiles is placed together with the Alveolata (includes Chromerida, Apicomplexa and Dinoflagellata) and Rhizaria (includes Chlorarachniophyta that have green-plastids), these groups are collectively abbreviated as SAR. Haptophyta (group Chromalveolata) which is considered as a sister group to the SAR; and Cryptophyta was found to be more close to the group Viridiplantae (Burki et al. 2012), while the Euglenophyta (group Excavata) was distantly related to the above mentioned groups. Based on the phylogenetic analyses on the plastid level, there are evidences of secondary endosymbiotic events from either a Chlorophyta (green lineage) or a Rhodophyta (red lineage), but there are no reports of endosymbiotic events from a Glaucophyta. Chlorophyta, the green lineage undergoes two independent endosymbiotic events, where members of core families UTC (Ulvophyceae,Trebuxiophyceae, Chlorophyceae) and Prasinophyceae family leads to the origin of the Chlorarachniophyta (Rhizaria) and Euglenophyta (Excavata), respectively (Rogers et al. 2007, Turmel et al. 2009)...
eBook - ePubOrganelles, Genomes and Eukaryote Phylogeny
An Evolutionary Synthesis in the Age of Genomics
- Robert P Hirt, David S. Horner(Authors)
- 2004(Publication Date)
- CRC Press(Publisher)
...For glaucocystophytes, there is little molecular data from nuclear genes, but some genes show them branching with the red or green algae, or both (e.g., Stibitz et al., 2000), and two multigene analyses also concluded that the red and green algae were closely related to the glaucocystophytes (Baldauf et al., 2000; Moreira et al., 2000). Altogether, the consistent picture coming from plastid genes, mitochondrial genes and nuclear genes is the same: red, green and glaucocystophyte algae share a common ancestor, and the origin of primary plastids can reasonably be inferred to trace back to a single endosymbiotic event. 3.4 Three Lineages At present, primary plastids are found in only three lineages of eukaryotes: the glaucocystophytes, the red algae and the green algae (and their land plant relatives). Land plants and green algae are a pervasive and dominant group of eukaryotes. Green algae are found in almost every aquatic and marine environment known and are an extremely diverse and specious group. The green algal lineage is deeply divided into two major subgroups, the chlorophytes and streptophytes, and land plants evolved from within the streptophyte clade. Green algae and land plants are characterized by the presence of chlorophylls a and b in their plastid. Red algae are also a very diverse and specious group. They are predominantly marine but are also present in freshwater environments, and some red algae inhabit relatively hostile environments such as high heat or high salinity. Certain red algae have evolved a complex form of multicellularity not unlike plants in many respects. Red algal plastids are also distinctive as they contain chlorophyll a and phycobilins, the latter being accessory pigments associated with structures called phycobilisomes that are visible by electron microscopy on the outside of the inner plastid membrane. Glaucocystophytes are a relatively small group of algae, with only three genera and a handful of species...
eBook - ePub- Simon Baker, Jane Nicklin, Caroline Griffiths(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...A suggested taxonomic scheme is shown in Figure 1 and characteristics of the major monophyletic groups are shown in Table 1. Only those organisms included in the microbial world will be discussed here. Three supergroups, the Archaeplastida, Excavata, and Chromalveolata, have been proposed, which include most of the previous chlorophytan and protistan organisms. The Amoebozoa contain the amebae, and current work indicates that this branch of the eukaryotic tree is a sister group of the fungi within the opisthokonts. The organisms once considered as basal branches to the eukaryotic tree have now been shown not to be primitive, amitochondrial species (i.e. lacking mitochondria), but to have affinities with flagellate species in the Excavates. Structure of the Archaeplastida: chlorophytes The Archaeplastida contain the blue green algae, green algae, red algae, and higher plants. Only the green algae, the chlorophytes, are considered to be eukaryotic microorganisms. The chlorophytes are a monophyletic group and they range in complexity from unicellular motile or nonmotile organisms to sheets, filaments, and coenocytes (Figure 2). They are found in fresh and salt water, in soil, and on and in plants and animals. Most chlorophytan cell walls are formed from cellulose and they may be fibrillar, similar to those of the fungi, and sometimes impregnated with silica or calcium carbonate. Chlorophytan cells contain nuclei, mitochondria, ribosomes, Golgi, and chloroplasts (Section H2). The internal cell structure is supported by a network of microtubules and endoplasmic reticulum. Chloroplasts in this group are very variable structures; they can be large and single, multiple, ribbon-like or stellate chloroplasts with chlorophylls a and b and carotenoids and they store starch. Chlorophytan cells have a vegetative phase that is haploid, and sexual reproduction occurs when cells are stimulated to produce gametes instead of normal vegetative cells at binary fission. Figure 1...
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...As a consequence, the way in which certain algae are grouped today may change once more is known about their ancestries. EVOLUTION AND PALEONTOLOGY OF ALGAE Ancient lineages of algae are believed to have given rise to a number of different organisms, ranging from green plants to protozoan euglenophytes. The latter are believed to have arisen from an ancient lineage of algae that included some zooflagellates, which is supported by ultrastructural and molecular data. Some scientists consider the colourless euglenophytes to be an older group and believe that the chloroplasts were incorporated by symbiogenesis more recently. The order of algae with the best fossil record are the Dasycladales, which are calcified unicellar forms of elegant construction dating back at least to the Triassic Period. Some scientists consider the red algae, which bear little resemblance to any other group of organisms, to be very primitive eukaryotes that evolved from the prokaryotic blue-green algae (cyanobacteria). Evidence in support of this view includes the nearly identical photosynthetic pigments and the very similar starches among the red algae and the blue-green algae. Many scientists, however, attribute the similarity to an endosymbiotic origin of the red algal chloroplast from a blue-green algal symbiont. Other scientists suggest that the red algae evolved from the cryptophytes (unicellular, aquatic algae), with the loss of flagella, or from fungi by obtaining a chloroplast. In support of this view are similarities in mitosis and in cell wall plugs, special structures inserted into holes in the cell walls that interconnect cells. Some evidence suggests that such plugs regulate the intercellular movement of solutes. Ribosomal gene sequence data from studies in molecular biology suggest that the red algae arose along with animal, fungal, and green plant lineages. The green algae are evolutionarily related, but their origins are unclear...
eBook - ePub- Andrew Lack, David Evans(Authors)
- 2021(Publication Date)
- Taylor & Francis(Publisher)
...Among eukaryotes three main multicellular kingdoms are recognized: animals, plants and fungi. The remaining eukaryotes are mainly unicellular but with a few multicellular groups such as slime molds and large algae. They are a heterogeneous group, forming several kingdoms of equivalent status to the three large ones and referred to for convenience, as the protists. There is no clear boundary between protists and plants and authors differ in which organisms they include within the plants. Multicellular green algae have many features in common with land plants and are the modern group closest to the ancestors of plants. Along with the brown algae and red algae, they are the dominant photosynthetic organisms in shallow seas. These three algal groups form quite separate evolutionary lines. Unicellular planktonic groups, again from several different evolutionary origins among the protists, form the basis of the food chain in the deep sea. All these algae are photosynthetic and are considered in this book only for comparison with the true plants in Topic 01. Other protists, animals and fungi will not be considered further except in relation to plants. Plant groups other than flowering plants, such as mosses, ferns and conifers, differ in various ways and these are considered in sections O, P and Q. Unifying features of plants Evidence from morphology and from DNA suggests that all plants share an ancestor among the green algae dating from between 450 and 500 million years ago in the Silurian era, perhaps earlier. To characterize the features that define plants as different from other eukaryotes is almost impossible since every feature has exceptions, but usually these exceptions are among plants that have lost the feature or are shared with some algae. They are photosynthetic and obtain all their nutrients from inorganic sources, i.e. they are autotrophic and the start of a food chain. The large algae and many planktonic protists are also photosynthetic...
eBook - ePubMarine Microbiology
Ecology & Applications
- Colin Munn, Colin B. Munn(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...These discoveries have important implications for theories on the origin of eukaryotes, discussed in Box 5.1. Figure 5.1 Frequency of sequences for archaeal phyla from samples of marine water, sediments, and hydrothermal vents. Data obtained from Schloss et al. (2016). Figure 5.2 A schematic representation of changes in our understanding of the relationships between eukaryotes and archaea over the past 40 years. The DPANN group contains the Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanoarchaeota, and Nanohaloarchaeota phyla. It is shown as a monophyletic lineage, although this is a topic of debate. Reprinted from Eme et al. (2017) with permission from Springer Nature. It is suspected that many of these new species may exist in close associations with other bacteria or archaea and may form syntrophic partnerships. As our knowledge of archaeal diversity grows, it is likely that a wide range of novel metabolic functions will be uncovered, but the overwhelming importance of archaea in marine environments lies in their activities in the production and oxidation of methane and in autotrophy linked to nitrification, discussed below. BOX 5.1 RESEARCH FOCUS Evolution of an evolutionary pathway—changing views of Archaea in the tree of life Woese and Fox (1977) recognized three distinct primary groupings of life on Earth. These ideas were consolidated in the highly influential paper by Woese et al. (1990)—it has >6500 citations to date—proposing the three domains: Bacteria, Archaea, and Eukarya (see Chapter 1). There was already considerable acceptance of the endosymbiosis theory, in which the eukaryotic cell type is believed to have been formed from a chimera of ancestral archaeal cells with ancestral bacterial cells, with strong genetic evidence that mitochondria are descended from alphaproteobacterial endosymbionts. However, the nature of the archaeal partner has proved much more difficult to establish and promoted much debate. Eme et al...
eBook - ePub- Donald Kaplan, Chelsea D. Specht(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
...The existence of such a protoplasmic unity leaves little doubt that we are dealing with a true parenchyma in these species. FIGURE 3.42 Apical meristem of the uniaxial red alga Platysiphonia. (From Bold and Wynne, 1985.) The Biological Significance of Multicellularity in Plants If we conclude that multicellularity in plants is not the cause of their growth or shape but merely one of the correlates of a plant's morphogenesis, what then is the value of having the plant's protoplast cleaved into these subunits we traditionally have called cells? Here again, we can draw upon our broad comparative perspective of other plant groups for insights. One of the primary roles of multicellularity is mechanical support. The honeycomb network of intersecting rigid cell walls is undoubtedly a major factor permitting plants to be self-standing in a land environment. We see such a diversity of patterns of cellularity preserved in the course of evolution in the algae because the aquatic environment has not selected against any of these alternatives. However, once plants invaded the land, presumably only the multicellular, parenchymatous type of body construction supplied the kind of three-dimensional support that allowed them to function as free-standing photoautotrophs. Thus as Hagemann (1982) has suggested, the development of “cells” as we know them in plants with their own set of organelles and one nucleus was the price paid for the erection of such a wall stabilizing system. Hence the concept of the “cell” in plants is of an entirely different nature from that of animals. Support for such interpretations comes from analogies to walls that we find in some of the larger siphonous algae...
