Freezing tolerance of transgenic tobacco with increased content of unsaturated fatty acid by expressing the CvFad2 or CvFad3 gene

Two fatty acid desaturases were independently expressed in tobacco plants and freezing tolerance of the transgenic plants was investigated: the two desaturases were CvFAD2, which desaturates microsomal C18:1 (oleic acid) to C18:2 (linoleic acid), and CvFAD3, which desaturates microsomal C18:2 to C18:3 (linolenic acid). Fatty acid composition analysis showed that the C18:2 contents in the plants transformed with pBE2113/CvFad2 did not increase compared with that of the wild-type plant. However, an increase in the C18:3 content by 2.4% was observed in the line of No. 19 although the increase was not statistically significant. In the plant transformed with pBE2113/CvFad3, the C18:3 content increased by 6.4% compared with that of the wild-type plant. Measurement of the electrolyte leakage of the leaves showed that freezing tolerance of the CvFad2 plant was a little higher than that of the wild-type plant at all temperatures investigated (from -1 to -4°C). Contrary to the case of the CvFad2, the freezing tolerance of the CvFad3 plant tended to be slightly lower than that of the wild-type at all temperatures tested despite the unsaturation levels of the plant were higher than those of the CvFad2 plants.