Chromalveolata

2 Key excerpts on "Chromalveolata"

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  BIOS Instant Notes in Microbiology

  • Simon Baker, Jane Nicklin, Caroline Griffiths(Authors)
  • 2011(Publication Date)
  • Taylor & Francis

    (Publisher)

  SECTION J – ARCHAEPLASTIDA, EXCAVATA,Chromalveolata, AND AMOEBOZOA

  J1Taxonomy and Structure

  Key Notes

  Taxonomy of the Archaeplastida, Excavata, Chromal veolata, and Amoebozoa	Until fairly recently, the photosynthetic and nonphotosynthetic protistan genera were divided into two polyphyletic form groups, the algae and protozoa, based on the presence or absence of chloroplasts. Currently, a monophyletic taxonomy of the protista is being developed, based on molecular data. Three supergroups of eukaryotic microorganisms are currently proposed, the Archaeplastida, Excavata, and Chromalveolata. The Amoebozoa are currently under revision.
  Structure of the Archaeplastida: chlorophytes	Members of the Archaeplastida considered as microorganisms are unicellular, photosynthetic organisms belonging to the chlorophytes (green algae). Some have a filamentous or membranous morphology. They have a cellulose cell wall. Many species are flagellate, and they contain chloroplasts, which vary in structure and pigment content
  Structure of the Excavata, Chromalveolata, and Amoebozoa	Members of the Excavata and Chromalveolata are heterotrophic or photosynthetic, unicellular eukaryotes. They vary greatly in shape and size, and contain most eukaryotic cell organelles. They also have some unique organelles. There are three groups within the Excavata, the euglenids, kinetoplastids, and fornicata, and within the Chromalveolata there are the alveolates (ciliates, dinoflagellates, and apicomplexans) and the stramenopiles (diatoms, chrysophytes, oomycetes, and opalines). Species in the Amoebozoa are naked, heterotrophic cells with an absorptive nutrition.
  Growth in the Archaeplastida, Excavata, Chromalveolata, and Amoebozoa	Growth in the unicellular species is synonymous with longitudinal binary fission, but budding and multiple fissions occur in some groups. Coenocytic, tubular or filamentous species grow by tip growth like the fungi. Other filamentous or membranous species grow by intussusception of new cells into the filament. The kinetics of growth of unicellular species are similar to those of bacteria, but in addition to estimations of growth by mass measurement, cell counts and chlorophyll content can be assessed. Rapid cell division can lead to very high cell populations, only limited by nitrogen, phosphate or silicon availability.

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  Light Harvesting in Photosynthesis

  • Roberta Croce, Rienk van Grondelle, Herbert van Amerongen, Ivo van Stokkum(Authors)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Cyanobacteria, green algae, and higher plants are usually well studied in photosynthesis research, but our knowledge about all other eukaryotic photosynthetic algae is far less advanced. Evolutionarily, the eukaryotic phototrophs fall into four main groups: (1) glaucophytes, which, in a simplified view, resemble eukaryotic cells with a cyanobacterium within; (2) the red algae, which also contain phycobilisomes as major antenna complexes comparable to those of Cyanophyta; (3) the “green lineage,” comprising green alga, mosses, ferns, and higher plants, but also Euglenophyta and Chlorarachniophyta; and (4) a rather diverse group called chromalveolates. Whereas glaucophytes, green and red algae evolved after a primary endosymbiosis between a cyanobacterium and a host eukaryote, chromalveolates are the result of one or several secondary endosymbioses between two eukaryotes, one of them already photosynthetic and most probably related to extant red algae (Archibald and Keeling 2002). This symbiont became reduced to almost only the chloroplast, which is surrounded by more than two membranes, whereby the inner two are the canonical chloroplast envelope membranes known from all other eukaryotic phototrophs. Additionally, one or two further membranes surround the secondary plastids, and the outer one is connected to the nuclear endoplasmic reticulum. The space between the two inner membranes and the outer ones represents the original cytosol of the endosymbiont and contains a nucleomorph in some cases, for example, in cryptophytes. This nucleomorph is a remnant of the symbionts’ nucleus, and if present, the so-called periplastid compartment also contains active eukaryotic ribosomes (Maier et al. 1991).

  Members of chromalveolates are cryptophytes, haptophytes, heterokonts (including among others brown algae and diatoms), as well as alveolates, which include the photosynthetic dinoflagellates (Dinophyta), and a newly discovered group, the Chromeridae. The current knowledge about light-harvesting systems in most of these groups is very limited, with by far the most research done on diatoms and dinoflagellates. In this chapter, a general overview about the pigments and the genes for antenna proteins will be given first, followed by the known light-harvesting systems of chromalveolates, with a special focus on cryptophytes, dinophytes, and diatoms. The reader is also referred to the excellent review of MacPherson and Hiller (2003).

  8.2Light-harvesting systems in the different chlorophyll

  c

  –containing algal groups

  8.2.1Pigments

  All photosynthetic eukaryotes use chlorophyll (Chl) a as photosynthetic pigment, accompanied by several accessory chromophores (see also Chapters 1 and 3 ). In chromalveolates, no Chl b is present and is mostly replaced by different forms of Chl c. This accounts for the synonym “Chl c–containing algae” for chromalveolates, although some do not even contain a second Chl besides Chl a, and prasinophytes—a group related to the green lineage—contain Chl c– or Chl c–like pigments, as well (Six et al. 2005, Wilhelm and Lenartz-Weiler 1987). In all types of Chl c, the phytol ester is lacking and their spectral signature is dominated by a huge Soret band absorption around 465 nm in organic solvent, with about three times the extinction coefficient of Chl a in its Soret maximum (Figure 8.1 ). In contrast, the QY absorption at around 630 nm is minor, with only about a quarter of the extinction of Chl a in its QY band. Three different kinds of Chl c exist, distinguished by their residues at the porphyrin ring. In Chls c2 and c3 , this residue contains a double bond which is part of the conjugated system. Thus, these absorb at slightly longer wavelengths as compared to Chl c1 . In haptophytes Chl c3 and in dinoflagellates Chl c2 were described as the major Chl c, whereas diatoms usually contain Chl c1 and some Chl c2 as well (Fawley 1989, Jeffrey and Humphrey 1975, Kraay et al. 1992). The two chlorophylls are accompanied by different xanthophylls. In diatoms, fucoxanthin (Fx) is the major carotenoid, whereas in dinoflagellates peridinin (Per) takes its function. Both are peculiar with a carbonyl moiety in conjugation with the polyene backbone (Damjanović et al. 2000, Frank et al. 2000, Katoh et al. 1991, Zigmantas et al. 2004). A special case are cryptophytes, where phycobilins, but not in the form of phycobilisomes, are located in the thylakoid lumen as accessory pigments. In addition, the carotenoid alloxanthin is present (Table 8.1

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