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JXB Advance Access published online on February 10, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erj075
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© The Author [2006]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received May 30, 2005
Accepted November 25, 2005

RESEARCH PAPER

Contribution of omega-3 fatty acid desaturase and 3-ketoacyl-ACP synthase II (KASII) genes in the modulation of glycerolipid fatty acid composition during cold acclimation in birch leaves

Françoise Martz 1 *, Sari Kiviniemi 2, Tapio E. Palva 3, and Marja-Liisa Sutinen 4

1 Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, FIN-96301 Rovaniemi, Finland
2 Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, FIN-96301 Rovaniemi, Finland; Present address: Chemistry Department, University of Oulu, PL 3000, FIN-90014 University of Oulu, Finland
3 Department of Biological and Environmental Sciences, Faculty of Biosciences, University of Helsinki, PL 56, FIN-00014 Helsinki, Finland
4 Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, FIN-96301 Rovaniemi, Finland; Present address: Finnish Forest Research Station, Muhos Research Station, Kirkkosaarentie 7, FIN-91500 Muhos, Finland

* To whom correspondence should be addressed.
Françoise Martz, E-mail: francoise.martz{at}metla.fi


  Abstract

Temperate and boreal tree species respond to low positive temperatures (LT) or a shortening of the photoperiod (SD) by inducing cold acclimation. One of the metabolic consequences of cold acclimation is an increase in fatty acid (FA) desaturation in membrane lipids, which allows functional membrane fluidity to be maintained at LT. The molecular mechanisms of FA desaturation were investigated in leaves of birch seedlings (Betula pendula) during cold acclimation. Four genes involved in FA biosynthesis were isolated: a 3-ketoacyl-ACP synthase II gene (BpKASII) involved in the elongation of palmitoyl-ACP to stearoyl-ACP, and three {omega}-3 FA desaturase genes (BpFAD3, BpFAD7, and BpFAD8) involved in the desaturation of linoleic acid (18:2) to {alpha}-linolenic acid (18:3). BpFAD7 was the main {omega}-3 FAD gene expressed in birch leaves, and it was down-regulated by LT under SD conditions. LT induced the expression of BpFAD3 and BpFAD8 and a synchronous increase in 18:3 occurred in glycerolipids. Changes in the photoperiod did not affect the LT-induced increase in 18:3 in chloroplast lipids (MGDG, DGDG, PG), but it modulated the LT response detected in extra-chloroplastic lipids (PC, PE, PI, PS). A decrease in the proportion of the 16-carbon FAs in lipids occurred at LT, possibly in relation to the regulation of BpKASII expression at LT. These results suggest that LT affects the whole FA biosynthesis pathway. They support a co-ordinated action of microsomal (BpFAD3) and chloroplast enzymes (BpFAD7, BpFAD8) in determining the level of 18:3 in extra-chloroplastic membranes, and they highlight the importance of dynamic lipid trafficking.

Keywords: Cold acclimation; fatty acid; freezing resistance; linoleic acid; low temperature; omega-3 fatty acid desaturase; short photoperiod.
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