The chlorophitic are a type of algae and one of the components of the lineage viridiplantae, along with terrestrial plants. These green algae are a diverse group of organisms present in aquatic habitats, and sometimes in terrestrial habitats.
These organisms have played key roles in ecosystems for hundreds of millions of years. The evolution of land plants is believed to have arisen from a chlorophyte-type ancestor. This was a key event in the evolution of life on Earth, which led to a drastic change in the planet's environment, initiating the complete development of terrestrial ecosystems.
Green algae on a rock on the beach in Corfu. By Kritzolina
The most accepted theory at present about the appearance of chlorophytes is the endosymbiotic one. This theory defends that a heterotrophic organism captured a cyanobacterium, with which it was stably integrated.
Green algae have characteristics similar to land plants, such as having double-membrane chloroplasts, with laminated thylakoids that contain chlorophyll a and b, along with other accessory pigments such as carotenes and xanthophylls.
characteristics
This group of green algae exhibit a marked variation in morphology, reflecting the ecological and evolutionary characteristics of the habitat where they arose. The range of morphological diversity ranges from the smallest free-living eukaryote, Ostreococcus tauri, to various multicellular life forms.
Chlorophytes are organisms that share several cellular characteristics with land plants. These organisms have chloroplasts enclosed by a double membrane, with laminated thylakoids.
Chloroplasts of chlorophytes generally have a structure in their stroma called pyrenoid. The pyrenoid is a protein mass, rich in the enzyme Ribulose-1,5-bisphosphate-carboxylase-oxygenase (RuBisCO), which is responsible for the fixation of CO 2.
Most chlorophytes have a firm cell wall with a matrix that is made up of cellulose fiber. Flagellate cells possess a pair of flagella that are similar in structure, but may be different in length. The flagellar transition zone (the region between the flagellum and the basal body) is typically characterized as having a nine-pointed star shape.
Habitat and distribution
Chlorophytes are typically abundant in freshwater environments, including lakes, ponds, streams, and wetlands. In these places they can become a nuisance in conditions of nutrient contamination.
Only two groups of chlorophytes have been found in marine environments. Marine green algae (Ulvophyceae) abound in coastal habitats. Some marine green algae (mainly Ulva) can form extensive floating coastal blooms, called “green tide”. Other species, such as Caulerpa and Codium, are notorious for their invasive nature.
Some groups of chlorophytes, for example the Trentepohliales, are exclusively terrestrial and are never found in aquatic environments.
Caulerpa geminata Harv. Auckland Museum
Some chlorophyte lineages can be found in symbiosis with a diverse range of eukaryotes, including fungi, lichens, ciliates, foraminifera, cnidarians, mollusks (nudibranchs and giant clams), and vertebrates.
Others have evolved to have an obligate heterotrophic lifestyle as parasites or free-living species. For example, the green algae Prototheca grows in sewage and soil and can cause infections in humans and animals known as protothecosis.
Feeding
As mentioned above, chlorophytes are autotrophic organisms, which means that they are capable of making their own food. This peculiarity is shared with terrestrial plants, and they achieve it through a biochemical process called photosynthesis.
First, solar energy is captured by a group of pigments (Chlorophyll a and b), to later be transformed into chemical energy, through a set of oxide-reduction reactions.
This process is carried out in the thylakoid membrane (within the chloroplasts), which is embedded in the protein complex in charge of transforming light energy into chemical energy.
The light is first received by the pigments within the antenna complex, which directs the energy to chlorophyll a, which is responsible for providing the photochemical energy, in the form of electrons, to the rest of the system. This leads to the production of molecules with high energy potential such as ATP and NADPH.
Next, ATP and NADPH are used in the Calvin cycle, in which the enzyme Ribulose-1,5-bisphosphate-carboxylase-oxygenase (RuBisCO), is in charge of converting atmospheric CO 2 into carbohydrates. In fact, thanks to the study of a chlorophyte, Chlorella, the Calvin cycle was elucidated for the first time.
Reproduction
Unicellular chlorophytes reproduce asexually by binary fission, while filamentous and colonial species can reproduce by fragmentation of the algae body.
Sexually they can be reproduced by hologamy, which occurs when the entire alga functions as a gamete, fusing with another equal. This can occur in single-celled algae.
Conjugation, meanwhile, is another very common means of sexual reproduction in filamentous species, in which one alga functions as a donor (male) and another as a recipient (female).
The transfer of cellular content is carried out by means of a bridge called a conjugation tube. This produces a zygospore, which can remain dormant for a long time.
Another type of sexual reproduction is planogamy, which consists of the production of mobile gametes, both male and female. Finally, oogamy is a type of sexual reproduction that consists of the appearance of an immobile female gamete that is fertilized by a mobile male gamete.
Applications
Chlorophytes are photosynthetic organisms capable of producing numerous bioactive components that can be used for commercial use.
The potential of photosynthesis carried out by microalgae in the production of components with high economic value or for energy use is widely recognized, due to its efficiency in the use of sunlight compared to higher plants.
Chlorophytes can be used to produce a wide range of metabolites such as proteins, lipids, carbohydrates, carotenoids or vitamins for health, nutrition, food additives and cosmetics.
The freshwater chlorophyte Haematococcus pluvialis. Wiedehopf20
The use of chlorophytes by humans dates back 2000 years. However, biotechnology related to chlorophytes really began to develop in the middle of the last century.
Today the commercial applications of these green algae range from use as a food supplement to the production of concentrated animal feed.
References
- Round, FE, 1963. The taxonomy of the Chlorophyta, British Phycological Bulletin, 2: 4, 224-235, DOI: 10.1080 / 00071616300650061
- Eonseon, J., Lee, CG, Pelle, JE, 2006. Secondary carotenoid accumulation in Haematococcus (Chlorophyceae): Biosynthesis, regulation, and biotechnology. Journal of Microbiology and biotechnology, 16 (6): 821-831
- Fang, L., Leliaert, F., Zhang, ZH, Penny, D., Zhong, BJ, 2017. Evolution of the Chlorophyta: Insights fromchloroplast phylogenomic analyzes. Journal of Systematics and Evolution, 55 (4): 322-332
- Leliaert, F., Smith, DR, Moreau, H., Herron, MD, Verbruggen, H., Delwiche, CF, De Clerck, O., 2012. Phylogeny and Molecular Evolution of the Green Algae. Critical reviews in plants science, 31: 1-46
- Priyadarshani, I., Rath, B., 2012. Commercial and industrial applications of micro algae - A review. Journal Algal Biomass Utilization, 3 (4): 89-100