Abstract:

To explore the effects of salicylic acid（SA）on fatty acid compositions in cucumber （Cucumis sativus L.）seedlings under low temperature，the changes in total contents of fatty acids and relative content of each composition，as well as the expression levels of fatty acid desaturase genes（CsFADs）were detected. The results showed that SA application could repress the low temperature- induced increase in malondialdehyde content and relative electrolyte leakages，and maintain the stability of cell membranes. Under low temperature，total contents of fatty acids were decreased. Especially，the relative contents of polyunsaturated fatty acids（e.g. C_18:3）were decreased，while the ratio of C_18:0 and C_18:1 increased. Thereby，the double bond index of fatty acid was reduced. After SA application，both total contents and unsaturation degree of fatty acid could be restored. Low temperature could induce the  expression of CsFAD genes. After SA application，the induction folds of CsFAB2.1，CsFAB2.2，CsFAD2.1 and CsFAD7 were significantly increased. In summary，in the cucumber seedlings exposed to low temperature，exogenous application of SA could induce the expression of CsFAD genes to increase the unsaturation degree of fatty acids，thereby enhance the stability of cell membranes，and finally increase the stress tolerance of seedlings.

Key words: cucumber, fatty acid, salicylic acid, fatty acid desaturase（FAD）, low temperature