Abstract: Meythyl Jasmonate (MeJA) is an elicitor for defensive responses of plant to pathogens, while NO and H₂O₂ are signal molecules related to defensive responses. In this study, MeJA-induced defense responses of apple suspension cells were monitored in NO release, H₂O₂ accumulation, PAL activity and MDA content, with sodium nitroprusside (SNP) as a NO donor, L-NAA (Nx-nitro-L-arginine) as NOS inhibitor and PTIO (2-phenyl-4,4,5,5-tetramethyl- imidazoline-1-oxyl-3-oxide) as NO scavengers. The results showed that apple suspension cells constantly produced NO and reached a peak release at 6h when exposed to MeJA treatment. On the contrary, L-NAA and PTIO inhibited the generation of NO in cells. MeJA treatment also led to a great increase in H₂O₂ level in suspension cells, but SNP treatment did not. In addition, PAL activities as well as MDA and phytoalexin contents displayed similar dynamic curves with different treatments, increasing firstly and then decreasing with peak activity or content at 4-6h. Those findings indicated that MeJA induced the generation of NO, and then MeJA and NO worked together to increase H₂O₂ level in suspension cells. Phytoalexin and MDA increase as well as PAL activity enhancement were mainly induced by NO, although it seemed other signals involved.

Key words: apple, suspension cells, elicitor, NO, MeJA, PAL, phytoalexin