The role of ascorbic acid in plant-pathogen interactions

Abstract

Ascorbic acid (AsA) is one of the most abundant antioxidant molecules in plants. AsA provides the first line of defense against damaging reactive oxygen species (ROS), protecting plant cells from many environmental factors that induce oxidative stress, including wounding, ozone, high salinity, and pathogen attacks. AsA interacts with key elements of a complex network orchestrating plant defense mechanisms, thereby influencing the outcome of plant-pathogen interaction. It can act in coordination with glutathione (GSH) and important enzymatic antioxidants in the AsA-GSH cycle to provide the appropriate redox environment regulating diverse defense pathways such as the expression of defense genes through the activation of the NPR1 (Nonexpressor of Pathogenesis-Related protein 1) regulatory transcription factor, the strengthening of cell walls, and the modulation of defense-hormonal signalling networks. On the other hand, AsA was found to act either as an inducer per se or as a component of induced resistance (IR) process to pathogens when elicited by other inducers/elicitors such as ß-aminobutyric acid (BABA, a non-proteinic amino acid), jasmonic acid (JA) and its methyl ester (methyljasmonate, MEJA), and extracellular polysaccharides (EPSs). This chapter provides a broad picture on the mechanisms by which AsA interacts with key components of a complex network regulating both basal and induced resistance in different pathosystems.