Singh et al. (2004)reported that salicylic acid activated a cascade of events resulting in the inhibition of viral replication and
their cell-to-cell and long distance transmission in plants. Lower
concentrations of salicylic acid were found to enhance the deposition of callose plugs in Arabidopsiswhich contributed to the
plant defense system (Kohler et al., 2002).Lamb and Dixon (1997)
reported that salicylic acid causes an increase in the accumulation of H2O2in plant tissues which plays a key role in initiating
hypersensitive responses and providing SAR against pathogenicmicrobes. Salicylic acid is found to alter the activity of a mitochondrial enzyme, alternative oxidase, which mediates the oxidation of
ubiquinol/ubiquinone pool and reduction of oxygen to water, without the synthesis of ATP in mitochondria and this altered activity of
enzyme alternative oxidase affects the ROS levels in mitochondria
and in turn induces an antiviral defense response in plants (Singh
et al., 2004).