Abstract: In order to study the differences in the expression of mitochondria-related genes during the process of cucumber PCD induced by salicylic acid（SA）and downy mildew as well as the way of PCD occurred in cucumber leaves,the leaves were treated with 10 mmol/L SA and inoculated with the spore suspensions（5×10⁵-10×10⁵ Spores /ml）of Pseudoperonospora cubensis at the four-leaf period of cucumber. Total RNAs were extracted from the leaves treated with SA after 0,3,12,and 24 h and the leaves treated with P. cubensis after 0,36,72,and 96 h. The expressions of the 16 mitochondria-related genes were analyzed using qRT-PCR techniques. The results showed that the 16 genes expressed after SA-treatment and P. cubensis infection with a similar or contrary expression trend,indicating that the genes with PCD induced by SA were significantly related to the signaling pathway of PCD induced by downy mildew. Eleven genes of them were up-regulated both in downy mildew treatment and in SA treatment,5 genes were up-regulated in SA treatment,but were down-regulated in downy mildew treatment,showing that there were differences in disease resistance signaling pathways induced between by SA and downy mildew,which then resulted in the different occurrence patterns of PCD in cucumber leaves. These 16 genes belonged to 4 functional groups,including mitochondrial membrane transport,cell respiration,protein synthesis,folding and transport,mitochondrial signal transduction and other unknown functions.

Key words: cucumber, salicylic acid, downy mildew, programmed cell death, mitochondrion