Mechanisms of Defence to Pathogens : Biochemistry and Physiology

Plant defences comprise both pre-existing barriers as well as defences induced upon perception of pathogen-associated molecular patterns (PAMPs) or microbe-associated molecular patterns (MAMPs) or molecules produced from damage as a result of infection (damage-associated molecular patterns (DAMPs)). This chapter focuses on the induced mechanisms of defence. The inducibility of phytoalexin biosynthesis has probably been favoured in the course of evolution by biological constraints such as metabolic costs and functional side-effects associated with chemical defence. Historically, the term ‘hypersensitive’ refers to the rapid and localized cell death induced in specific cereal cultivars by the fungal pathogen Puccinia graminis. The expression ‘hypersensitive response’ (HR) was coined later on when it appeared that this form of plant cell death was generally associated with resistance to many pathogens. Infection by pathogens is accompanied by the local and systemic induction of plant encoded proteins referred to as pathogenesis-related (PR) proteins