Abstract: 【Objective】To investigate the mechanism of cucumber lipoxygenase gene participating in the formation of fruit aldehyde aroma, a full length cDNA named CsLOX2 was cloned from the Northern China germplasm No. 26 and the sequence characteristics of CsLOX2 were analyzed. Furthermore, the expression mode, the relative C6 aldehyde content and the lipoxygenase activity of cucumber fruit during fruit development were studied. 【Method】The full length cDNA of CsLOX2 gene was cloned using the methods of RT-PCR and 3′RACE, and the structure and the coded protein were analyzed. The expression mode of CsLOX2 gene using Real-time PCR and LOX activity were measured during the fruit developing. The head space-solid phase microextraction (HS-SPME) combining with gas chromatography-mass spectrometry (GC-MS) method were used to measure the relative C6 aldehyde content of cucumber fruits. 【Result】The full length cDNA of cucumber lipoxygenase gene named CsLOX2 was 2 878 bp. The open reading frame encompassed 2 640 bp and encoded 879 polypeptides. The calculated protein molecular mass was 99.39 kD and isoelectric point was 6.28. The amino acids sequence of CsLOX2 shared three conserved regions and six highly conserved histidines with other plant LOXs. It showed that the sequence of CsLOX2 had high identity compared with other lipoxygenases by NCBI BLAST. The RT-PCR analysis showed that CsLOX2 gene expressed differently during the fruit development, and highest on the 3 d after anthesis, and then down-regulated gradually and lowest on the 15 d after anthesis. The total LOX activity rose from the 3 d to 12 d after anthesis, and it was up to the highest activity on the 12 d after anthesis, and then went down. The expression peak of CsLOX2 gene preceded that of the LOX activity during the fruit development. The relative C6 aldehyde content was higher at fruit early development stage and decreased gradually during the fruit development and which was the lowest on 12 d after anthesis.【Conclusion】A lipoxygenase gene CsLOX2 was cloned from the Northern China germplasm No. 26 by RT-PCR and RACE. The deduced amino acid sequence of CsLOX2 gene contained the conserved motifs of LOXs family. The expression peak of CsLOX2 gene preceded that of the LOX activity during the fruit development. This study will provide a basis for probing the mechanism of CsLOX2 gene participating in the biosynthesis of aldehydes of cucumber fruits.

Key words: Cucumis sativus(cucumber) , lipoxygenase , gene cloning , sequence analysis , real time-PCR , C6 aldehyde