An acclimation to the changing physicochemical conditions and high amount of Delta(12)-unsaturated fatty acids of the Antarctic Chlorella vulgaris NJ-7 prompted us to speculate about the involvement of Delta(12)-fatty acid desaturases (FAD) in its adaptation to the extremely unfavorable ambience. A full-length cDNA sequence, designated CvFAD6, was isolated from C. vulgaris NJ-7 via RT-PCR and RACE methods. Sequence alignment showed that the gene was homologous to corresponding Delta(12)-FAD from other eukaryotes. Phylogenetic analysis showed that it was grouped with plastidial Delta(12)-FAD with conserved histidine boxes. Yeast cells transformed with a plasmid construct containing CvFAD6 coding region accumulated a considerable amount of linoleic acid (18:2Delta(9,12)), normally not present in wild-type yeast cells, suggesting that the isolated gene encodes a functional Delta(12) enzyme. The correlation between the accumulation of CvFAD6 and temperature has been examined by real time PCR. The analysis showed a constant expression of CvFAD6 from 25 to 15 degrees C whereas a fourfold increased from 25 to 4 degrees C. Moreover, CvFAD6 transcription was more sensitive to saline stress since a 20-fold increase at 6% NaCl was detected. Our data demonstrate that CvFAD6 is the enzyme responsible for the Delta(12) fatty acids desaturation involved in low temperature and high salinity acclimation for Antarctic C. vulgaris NJ-7.