Abstract:

To explore the effects of salicylic acid（SA）on fatty acid compositions in the roots of
cucumber（Cucumis sativus L.）seedlings under low temperature，the changes in total fatty acid contents
and relative content of each composition，as well as expression levels of fatty acid desaturase（CsFAD）
genes were detected. The results showed that under low temperature，total fatty acid contents increased in
the roots of cucumber seedlings. The relative abundance of major saturated fatty acids（C16︰0 and C18︰
0）increased，while the main unsaturated fatty acid（C18︰3）decreased upon low temperature stress，and
thereby，the unsaturation degree and double bond index of fatty acid were reduced. After exogenous SA of fatty acid was restored. Low temperature could repress the expression of CsFAB2.1 ，CsFAB2.2
application，total fatty acid content did not show a significant difference. However，the relative abundances
of saturated fatty acids were decreased，while the unsaturated fatty acids were elevated，and therefore，the
unsaturation degree of fatty acid was restored. Low temperature could repress the expression of CsFAB2.1，
CsFAB2.2 and CsFAD5，and induce the expression of CsFAD3 and CsFAD7 in the roots. After SA
application，the inhibition of CsFAB2.1，CsFAB2.2 and CsFAB2.3 were released. The expression of
CsFAD2.1 was also significantly induced. In summary，under low temperature，exogenous application of
SA could induce the expression of CsFAD genes to increase the unsaturation degree of fatty acids，and
thereby remain the stability of cell membranes in the roots of cucumber seedlings，and finally increase the
cold stress tolerance of seedlings.

Key words: cucumber, root, low temperature, salicylic acid, fatty acid