page_title: Symbiodinium
section_title: Chloroplast
hierarchical_section_title: Symbiodinium / Morphology / Chloroplast
caption_attribution_description: English: The reticulated chloroplast structures of (A) Symbiodinium goreaui (type C1), (B) “S. fitti” (type A3), and (C) “S. californium” (type E1) imaged in 3-D using confocal microscopy of chlorophyll autofluorescence
context_page_description: Symbiodinium is a genus of dinoflagellates that encompasses the largest and most prevalent group of endosymbiotic dinoflagellates known. These unicellular algae commonly reside in the endoderm of tropical cnidarians such as corals, sea anemones, and jellyfish, where the products of their photosynthetic processing are exchanged in the host for inorganic molecules. They are also harbored by various species of demosponges, flatworms, mollusks such as the giant clams, foraminifera, and some ciliates. Generally, these dinoflagellates enter the host cell through phagocytosis, persist as intracellular symbionts, reproduce, and disperse to the environment. The exception is in most mollusks, where these symbionts are intercellular. Cnidarians that are associated with Symbiodinium occur mostly in warm oligotrophic, marine environments where they are often the dominant constituents of benthic communities. These dinoflagellates are therefore among the most abundant eukaryotic microbes found in coral reef ecosystems.
  Symbiodinium are colloquially called zooxanthellae, and animals symbiotic with algae in this genus are said to be "zooxanthellate".
context_section_description: Most described species possess a single, peripheral, reticulated chloroplast bounded by three membranes. The volume of the cell occupied by the chloroplast varies among species. The lamellae comprise three closely appressed (stacked) thylakoids, and are attached by two stalks to the pyrenoid surrounded by a starch sheath. In three of the described species, the thylakoids are in parallel arrays, but in S. pilosum, there are also peripheral lamellae. There are no thylakoid membranes invading the pyrenoid, which is unlike other symbiotic dinoflagellates. The lipid components of thylakoids include the galactolipids (monogalactosyl-diglycerides, digalactosyl-diglycerides), the sulpholipid, (sulphoquinovosyl-diglyceride), phosphatidyl glycerol, and phosphatidyl choline. Associated with these are various fatty acids. The light-harvesting and reaction centre components in the thylakoid membrane include a water-soluble peridinin-chlorophyll (chl.) a-protein complex (PCP), and a membrane-bound chl. a-chl. c2–peridinin- protein complex (acpPC), along with typical photosynthetic electron transport systems such as the photosystem II reaction centre and the chl. aP700 reaction centre complex of photosystem I. Also associated with the thylakoids are the xanthophylls dinoxanthin, diadinoxanthin, diatoxanthin and the carotene, B-carotene. The pyrenoid contains the nuclear-encoded enzyme type II Ribulose-bis-phosphate- carboxylase-oxygenase (Rubisco), which is responsible for the catalysis of inorganic carbon dioxide into organic compounds.
  All cultured isolates (i.e. strains) are capable of phenotypic adjustment in their capacity for light harvesting (i.e. photoacclimation), such as by altering the cellular Chl a and peridinin quota, as well as the size and number of photosynthetic units. However, the ability to acclimate is a reflection of genetic differences among species that are differently adapted (evolved) to a particular photic environment. For example, S. pilosum is characterized as a high light-adapted species, while others are low light-adapted (S. kawagutii) or adapted to a larger range in varying light fields (S. microadriaticum).
caption: The reticulated chloroplast structures of (A) Symbiodinium goreaui (type C1), (B) “S. fitti” (type A3), and (C) “S. californium” (type E1) imaged in 3-D using confocal microscopy of chlorophyll autofluorescence
exif: {}