The increased production of trienoic fatty acids, hexadecatrienoic (16:3) and linolenic (18:3) acids, is a response connected with cold acclimation of higher plants and is thought to protect plant cells against cold damage. Transgenic tobacco (Nicotiana tabacum cv SR1) plants that contain increased levels of 16:3 and 18:3 fatty acids, and correspondingly decreased levels of their precursors, hexadecadienoic and linoleic acids, were engineered by introduction of a chloroplast omega-3 fatty acid desaturase gene (the fad7 gene) isolated from Arabidopsis thaliana. When exposed to 1 degrees C for 7 d and then cultured at 25 degrees C, the suppression of leaf growth observed in the wild-type plants was significantly alleviated in the transgenic plants with the fad7 gene. The low-temperature-induced chlorosis was also much reduced in the plants transformed with the fad7 gene. These results indicate that increased levels of trienoic fatty acids in genetically engineered plants enhance cold tolerance.