Defense Responses of Cherry Rootstock Gisela 6' Elicited by Agrobacterium tumefaciens Infection

Agrobacterium tumefaciens causes crown gall disease in plants by transferring a portion of the tumor-inducing plasmid, transfer DNA, into the plant genome. To examine the physiological changes induced by A. tumefaciens in cherry rootstock Gisela 6', we determined the activity of defense-related enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), phenylalanine ammonialyase (PAL), lipoxygenase (LOX), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), and the content of phytohormones, salicylic acid (SA) and jasmonic acid (JA), in cherry plants before and after infection. Furthermore, we assayed the expression of genes encoding these enzymes and SA and JA biosynthesis genes using quantitative real-time PCR, and examined the morphology of the infected tissue surface. Infection with A. tumefaciens increased the activity of POD, SOD, PPO, APX, MDHAR, and GR, and upregulated the expression of the corresponding genes. It also elevated the JA content of cherry plants. No significant difference was noted in CAT and PAL activity between the infected and control groups. In the treatment group, a slight increase in LOX activity was observed at 15days post-infection (dpi), whereas DHAR activity declined by almost 50% at 10dpi. The total SA content showed a general upward trend in infected plants but did not show a clear difference compared with the control. Overall, our data suggest that Agrobacterium infection did not elicit a hypersensitive response in Gisela 6' but altered the expression level of genes involved in defense responses and phytohormone biosynthesis.