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The osmotic adjustment of marine microalgae and the complex role osmolytes play in this process

Kendall, L. (1996) The osmotic adjustment of marine microalgae and the complex role osmolytes play in this process. Master's Thesis / Essay, Biology.

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Abstract

Algae inhabit a wide variety of both marine and freshwater habitats. These habitats differ in regard to various factors such as chemical composition, the organisms that live there, the light which may radiate into that particular area, the temperature of the sites depending on where the environment is located, just to name a few. One factor that varies from environment to environment is the salinity. This paper will look at the mechanisms utilized by marine algae to cope with the changes in salinity content in their habitats and most importantly how they use different osmolytes to carry out this process. Marine algae "osmotically adjust" themselves to external salinity changes, in a biphasic maimer. Firstly, this includes changes in turgor pressure or large internal water fluxes in response to osmotic gradients. Secondly. an internally regulated osmotic adjustment occurs with the use of both inorganic and organic osmolytes. Compatible solutes are ions and molecules used by man organisms to osmotically adjust and they play a double role in the process of osmotic adjustment. They act as osmolytes and also protect the cellular enzymatic activities under salinity stress. They are called 'compatible solutes" because they protect the cellular enzymatic activity. The main compatible solutes are polyols (including amino acids, carbohydrates and sugars). quaternary ammonium derivatives or tertiary sulphonium compounds. Certain species and taxonomic classes use specific compatible solutes and some even use combinations of them. Glycerol is an important compatible solute because it plays a major role with glycolysis and interactions with enzymes of the Krebs cycle. β-dimethylsulphoniopropionate (DMSP) is a compatible solute that is produced in large quantities by marine microalgae as an osmoregulator. This compatible solute has also been suggested to be a cryoprotectant in marine microalgae that inhabit the cold waters of the polar region. Therefore. microalgae utilize DMSP for both osmoregulation and as a cryoprotectant. Some algae. e.g. the genus Dunaliella and some Chlamydomonas species, have an enhanced tolerance to salt. These salt-tolerant algae are referred to as halophils and their salt optima in relation to their growth rate differs from the normal salt tolerant species. They are salttolerant because they have an extreme tolerance of low water availability. Special types of marine microalgae with a similar salinity tolerance inhabit the Great Salt Lake. There are two main metabolic pathways that marine algae utilize in order to osmotically adjust under salinity stress. The first metabolic pathway is termed hyperosmotic stress by which an abundance of enzymes is synthesized and then osmolyes are produced. where the cellular metabolism is reduced, reserve products are remobilized and redistributed within the compartments of the cell. The second metabolic pathway is termed hypoosmotic stress in which polymeric reserve products are utilized, synthesis of enzymes is inhibited. degradative pathways are inhibited and organic osmolytes are released into the medium to protect the cell from rupturing by increased osmotic stress. These pathways function together in synchrony to enable marine micro-algae to survive in their environment.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:31
Last Modified: 15 Feb 2018 07:31
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9233

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