Study on the Extracellular Ice-Active Substances of Antarctic Sea Ice Algae Chlamydomonas sp. L4

Abstract: The ice-active substances associated with Antarctic sea ice diatoms were previously shown to have ice-binding activities. Ice-pitting activities were largely retained by dialysis membranes with molecular weight cut-offs of up to 300 kDa. These macromolecular substances cause pitting and other modifications of growing ice crystals. In this respect, they resemble fish antifreeze proteins, but unlike the antifreeze proteins they do not significantly lower the freezing point. Ice-active substances were not found in plants from temperate climates, but ice-activity was found to be associated with mosses from cold habitats in North America. Although the function of the ice-active substances is not known, their apparent confinement to cold environments suggests that they have a cryoprotective role.Ice-active substances (IASs) were found in 5 species of Antarctic ice algae,and the activity is different from different species,the Chlamydomonas sp. L4 contents more IASs than other Ice Algae. Ice-active substances are rife in Antarctic Ice Algae,they play important roles for the Ice Algae to adapting the cold environment。The concentration of the Ice-active substances of Antarctic ice microalga Chlamydomonas sp. L4 depends on the temperature,the concentration of the IASs rising remarkable along with the temperature down in the low section(4~8℃). the concentration keep steady in 8~12℃. the concentration of the IASs rising remarkable along with the temperature down, when the temperature close to the freezing point; the concentration of the IASs don’t have any relationship with the temperature, when the temperature away from the freezing point. In the same temperature, cold shock can improve the concentration of the IASs obviously.The results of SDS-PAGE and gel filtration on Sephadex G-200 show that the IASs of Antarctic ice microalga Chlamydomonas sp. L4 are a kind of things have continuous molecular weight, the result of coloration indicates that they were composed by carbohydrate and protein. The IASs of Chlamydomonas sp. L4 contained 73.3% carbohydrate and 17.8% protein,high content of carbohydrate assured the stability of the molecule. The molecular weight of IASs are usually very big, molecules were enwrapped by multilayer hydrophilic carbohydrate chains, and carbohydrate chains Maintains the stability of the entire molecular, protecting the molecules from being broken down by other molecules.The IASs of Antarctic ice microalga Chlamydomonas sp. L4 are stabile in extensive temperature section,The ice-pitting activity of IASs was destroyed by exposure to temperature 100℃, the stability probablely has relations with the special configuration of the glycoprotein. The carbohydrate chains provide protection to the peptide chains.IASs of Antarctic ice microalga Chlamydomonas sp. L4 can make the freezing speed slow comparing the BSA. And IASs can exhibit very high activity in a low concentration(0.1 mg·mL-1), but the ice-pitting activity was not increased when the canconcentration increased. Their function has remained unclear. The IASs are able to protect cells from freeze-thaw damage. To test this possibility, two species of marine diatom (one from Antarctic and one from temperate) were subjected to a single freeze–thaw cycle in the presence or absence of IAS. Viability, based on a double staining technique, was 26.2%~28.7% higher in the presence of IAS…
Key words: Antarctic sea ice microalgae; Chlamydomonas sp.L4; Ice-active substances; Antifreeze proteins; Glycoprotein; Ice-pitting

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