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JXB Advance Access published online on February 21, 2005
Journal of Experimental Botany, doi:10.1093/jxb/eri112
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Journal of Experimental Botany © Society for Experimental Biology 2005; all rights reserved
Received July 22, 2004
Accepted December 22, 2004

RESEARCH PAPER

Characterization of antifreeze activity in Antarctic plants

León A. Bravo 1* and Marilyn Griffith 2

1 Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile
2 Department of Biology, University of Waterloo, 200 University Ave. West, Waterloo, Ontario, N2L 3G1 Canada

* To whom correspondence should be addressed.
León A. Bravo, E-mail: lebravo{at}udec.cl


  Abstract

Deschampsia antarctica and Colobanthus quitensis are the only vascular plants to have colonized the Maritime Antarctic, which is characterized by its permanently low temperature and frequent summer frosts. To understand how the plants survive freezing temperatures year-round, antifreeze activity was assayed in apoplastic extracts obtained from both non-acclimated and cold-acclimated Antarctic plants. By observing the shape of ice crystals grown in dilution series of the extracts, it was found that D. antarctica had antifreeze activity, but C. quitensis did not. D. antarctica exhibited antifreeze activity in the non-acclimated state and this activity increased after cold acclimation. The antifreeze activity in D. antarctica was labile to proteolysis and high temperature, active over a wide pH range, and associated with molecules greater than 10 kDa in molecular weight. These results show that D. antarctica produces antifreeze proteins that are secreted into the apoplast. When examined by SDS-PAGE, the apoplastic extracts from cold-acclimated D. antarctica exhibited 13 polypeptides. It is concluded that D. antarctica accumulates AFPs as part of its mechanism of freezing tolerance. Moreover, this is the first plant in which antifreeze activity has been observed to be constitutive.

Keywords: Antarctic plants; antifreeze activity; apoplastic proteins; cold acclimation; Colobanthus quitensis; Deschampsia antarctica; freezing tolerance; ice.
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