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Dinoflagellate: Definition, Anatomy, Typical Life Cycle, Bioluminescence And Its Hazardous Toxins.

Dinoflagellate Definition

The dinoflagellate is a single-celled aquatic organism with two flagella. In the ocean, it is known to create bioluminescence. Dinoflagellate may be found in both fresh and saltwater and can create harmful quantities of neurotoxic compounds in high numbers. These creatures, which are midway between plants and animals, transform sunlight and organic matter eaten into energy. Dinoflagellates are producers in the food chain and offer a significant source of nutrition for aquatic primary consumers as a component of plankton.

Dinoflagellate Anatomy

Even though dinoflagellates are unicellular eukaryotes, their anatomy is complicated. They straddle the line between plant and animal life as one of the oldest forms of life.

Dinoflagellate is derived from the Greek words for spinning (dinos) and whipping (flagellate) (flagellum). The two flagella are described by the suffix. The morphology of the dinoflagellate Ceratium genus varies little; nonetheless, it is generally elongated (fusiform) with horns.

The most fundamental dinoflagellate morphology is a cell containing a transverse and longitudinal flagellum that is either armoured (thecate) or unarmored (athecate).

The transverse flagellum curls around the cell body like a wave. It oscillates to the left, propelling and rotating the dinoflagellate ahead. The longitudinal flagellum is located underneath the cell and beats at a slower rate.

The cell walls of thecate dinoflagellates are made out of cellulose plates that surround the amphiesma. The cell membrane, alveolae (structural vesicles), and several organelles make up the amphiesma. The cell walls of the thecates extend through these vesicles and combine to create an armoured shell. The dino-pellicle is a cellulose layer found underneath the alveolae of certain dinoflagellate species.

Pustule ducts create numerous sacs or vacuoles within the membrane. Their function is unknown at this time, despite the fact that it is more difficult for heterotrophic dinoflagellate organisms which do not obtain their nutrition from the sun. As a result, they are most likely involved in digestion.

The dinoflagellate organism has a significant number of organelles. Mitochondria, a nucleus, and secretory cysts are among them.

Only a few dinoflagellates get their energy from sunshine. Most are mixotrophic (digesting particles in their aqueous environment) rather than entirely photosynthetic (homotrophic). Plastids in both homotrophic phototropic and mixotrophic dinoflagellates generate and store food produced by photosynthesis. Amino acids, carbohydrates, and lipids are used to store this meal.

The Noctiluciphyceae are grouped together because of their ability to grab plastids (kleptochloroplasts) from surrounding microalgae. Chloroplasts constitute a kind of plastid. Some dinoflagellates include compartments within their plastids that assist the cell in manufacturing a source of carbon that can be converted into starch.

Dinoflagellates use osmosis and phagocytosis to obtain nutrients. Phagocytosis necessitates the absence of armour in the cell. The cytosome, or cell mouth, is present in athecate cells. Some cells consume unicellular organisms by rupturing outer membranes and drawing out their fluids via a peduncle, a hollow tube. Because the amount of food that armoured dinoflagellates can ingest is restricted, they may encircle their food supply with a pallium, a layer containing digestive enzymes.

Dinoflagellate stigmas or eyespots could have a role in light reception. The multiple dinoflagellate eyespots seem to help them migrate to light (positive phototaxis) and may influence the occurrence of luminescence.

Many dinoflagellate genera are bioluminescent, which means they can emit light. This is found as scintillons sprinkled along the vacuole’s periphery. Scintillons are cysts that contain the enzymes luciferase and luciferin. Both two enzymes remain separate and create light only until they come into contact. When they combine, they produce a bluish light that pulses or glows gently. Mostly at night, while eyespots cannot detect light, does this occur? The circadian cycle of dinoflagellates does not seem to be influenced by light intensity.

Dinoflagellate Life Cycle

Dinoflagellates are present in 80 percent of marine ecosystems and the remainder in freshwater habitats. As phototrophs, they turn sunlight into energy while also gaining energy from other species. Mixotrophic refers to a mixture of phototrophic and heterotrophic features. Mixotrophic dinoflagellates are the most common.

During the bulk of their lives, dinoflagellates are haploid. This implies that each cell has just one pair of chromosomes. They reproduce by dividing cells (asexual fission), while other species reproduce by becoming sex cells (gametes), which unite to form planozygotes. If conditions are unfavourable, planocytes produce hypnozygotes, which are walled, inactive cysts that stay latent till conditions are favorable.

The DNA of merged dinoflagellates goes through a procedure that is comparable to that of highly complicated multicellular creatures. The two single chromosomes are combined during nuclear cyclosis. They split into two haploid cells with mixed alleles later. Diversity is promoted when alleles are mixed.

Dinoflagellate cysts are readily distributed because they migrate through currents or are ingested by other animals. Dinoflagellates have thrived because of this trait.

Dinoflagellate Genus

It would take a long time to write out the complete dinoflagellate genus. There are around three thousand dinoflagellate species classified into several genera. The classification of this genus is much more perplexing. Dinoflagellates are eukaryotes. All through history, botanical and zoological classifications have been used.

The evolution of dinoflagellates has been explored in detail recently. In comparison to prior efforts, our greater understanding of molecular structures has resulted in drastically different categorization groupings.

The earlier classification of dinoflagellates is incorrect. As gene analysis of dinoflagellate DNA progresses, classification based on form and structure (morphology) is becoming obsolete.

Dinoflagellates’ cladistics (the evolution of shared characteristics) will not be fully revealed till DNA sequencing discloses their whole phylogeny. Most vary by source and focus only on cell shape and lifestyle. The term for this form of categorization is “linear taxonomy.”

In scientific circles, the Euteleost Tree of Life project is gathering momentum. This searchable non-molecular phylogenetic (ancestral history) map depicts the categorization of dinoflagellates from domain to superclass. Classes, orders, families, genera, and species are all quite identical to prior techniques after superclass. The evolutionary tree of dinoflagellates looks like this:

Domain: Eukaryotes

Kingdom: Chromalveolata

Supergroup or Clade 1: SAR

Clade 2: TSAR

Clade 3, or Infrakingdom: Alveolata

Phylum: Miozoa

Superclass: Dinoflagellata

Class:

  • Dinophyceae
  • Ellobiophyceae
  • Noctiluciphyceae
  • Oxyrrhidophyceae
  • Syndiniophyceae

Gymnodiniales of the class Dinophyceae, for example, have no armoured (thecate) exterior.

Oxyrrhinaceae of the order Oxyrrhinales and the class Oxyrrhidophyceae, for example.

For instance, Alexandrium is a genus. Algal blooms are very poisonous.

Dicroerisma psilonereiella, for example, belongs to the genus Dicroerisma, the family Actiniscaceae, the Order Actiniscales, and the class Dinophyceae. A marine species that was initially discovered in Canada.

The chromalveolata kingdom idea, which divides non-plants into species that generate energy via photosynthesis, is now being debated. Some dinoflagellate genera have lost this feature. DNA from non-phototropic dinoflagellates may still have the genetic information for photosynthesis even though this feature is no longer active.

Stramenopiles (two flagella), alveolates, and Rhizaria make up the unicellular eukaryotic supergroup TSAR (amoeba-like). The telonemid taxon (previously known as the Protist Kingdom) was introduced at a later evolutionary stage (TSAR). Each linked group (clade) has a common origin that has been created throughout a period of evolution.

Dinoflagellate Toxin

The Alexandrium genus of dinoflagellates generates reddish toxins which build up in shellfish without killing them. Paralytic shellfish poisoning may occur when people ingest infected shellfish, even when cooked at high temperatures.

Saxitoxin is the most common neurotoxic generator. Common symptoms include nausea, abdominal cramps, numbness in the tongue, prickling in the extremities, breathlessness, balance issues, and slurred speech. Poisoning from paralytic shellfish may be lethal. Large populations of marine animals have died as a result of it.

Amphidinium, a genus of dinoflagellates, is another potentially poisonous genus, albeit it is seldom lethal. Even at night, their latent cysts may pollute aquarium sand sold for sea fish exhibits since they stay near to the sand (unlike other species of dinoflagellates).

Dinoflagellate Bioluminescence

When dinoflagellate luciferin is oxidised, it produces light. This oxidation process can only take place when another enzyme called dinoflagellate luciferase is present.

The luciferin-luciferase response is present in cell scintillons, and it was first seen in lab fireflies. This method varies from dinoflagellate luminescence in that this dinoflagellate luminescence does not need adenosine triphosphate. It’s called firefly luminescence.

The vacuole of the cell must have an acidity level of roughly pH 6.3 to start the chemical process. This induces the luciferin-binding protein to release luciferin. In the presence of oxygen, dinoflagellate luciferinase enzymes may immediately attach to the liberated luciferin and generate an intermediate molecule. The oxidation of the associated luciferin-luciferinase complex results in the emission of light by this highly reactive intermediate. Proton-stimulated luminescence is the name for this method.

Flashing light emission and glow light emission are two kinds of dinoflagellate bioluminescence. Variations in vacuole acidity induce flashing, which is accompanied by dazzling, pulsating light. A glow is a light that persists but is not very bright.

Dinoflagellates are the most common eukaryotes in the ocean that produce bioluminescence because blue light goes the furthest through water. The Greeks observed marine phosphorescence as early as 500BC.

It is unknown why dinoflagellates create bioluminescence. The process may avoid the damaging effects of oxygen, according to certain theories. They also emphasise its use as a warning signal when first-order predators and marine consumers assault dinoflagellates. This warning might attract predators that prey on dinoflagellate feeding.

References

  • Falowski R, Knoll A (Eds). 2007. Evolution of Primary Producers in the Sea. San Diego, Elsevier Academic Press.
  • Durvasula SRV. 2020. Dinoflagellates: Classification, Evolution, Physiology and Ecological Significance. New York, Nova Science.
  • Spector DL (Ed). 1984. London, Academic Press.
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