Activation of defense responses in tomato plants infected with necrogenic and non necrogenic strains of cucumber mosaic virus

The increase in reactive oxygen species (ROS) has been found in plant cell in response to infection of various pathogens, including viruses. In the cell, the ROS level is controlled by enzymatic and not-enzymatic antioxidant systems. Among them, the ascorbate- glutathione cycle and other defence agents such as the enzymes catalase, superoxide dismutase and peroxidase prevent the accumulation of toxic level of H2O2 and other ROS. The objective of this study was to determine the changes of these soluble antioxidants in tomato plants infected with different strains of Cucumber mosaic virus (CMV). In particular, the antioxidant enzymes were examined in Solanum lycopersicum cv. UC82 plants inoculated with the aggressive strain CMV-Fny and with the same strain co-inoculated with a necrogenic variant of satellite RNA (CMV-Fny/77-satRNA), a combination inducing systemic necrosis and plant death. Analyses performed included both the transcriptional profiling and the determination of the enzymatic activity of such antioxidant components. In addition, gene expression analysis was carried out on genes involved in ethylene biosynthesis and signaling, in general defence responses and in programmed cell death (PCD) processes. Results showed that some of the antioxidative systems and components involved in PCD analyzed were commonly activated by both viral strains despite the different disease phenotype induced. Peculiar responses to either specific CMV inoculum were also detected, that could have some role in the determination of the observed disease phenotypes.