Chapter 9 – Hypersensitivity

Publisher Summary Hypersensitivity is a natural defense for plants in response to a variety of pathogens such as viruses, bacteria, fungi, and nematodes and is characterized by rapid cell death accompanied by an accumulation of toxic compounds within the dead cell. This chapter describes two completely different pictures of cell death: apoptosis and necrosis. Deficiency in energy and other resources forces the cell not to undergo the process of apoptosis, but follow a different algorithm of signals and events. The hypersensitive reaction is a feature of resistance among various types of incompatible interactions between plant and pathogen. This chapter explains the morphological alterations in cells during apoptosis and necrosis and compares their typical features in the form of a table. An essential role in programmed cell death, both in animals and plants, is played by mitochondria. Genes involved in plant cell death are also referred to as paranoid mutants. Genes regulating necrosis do not exist, because cell death at necrosis is reluctant and sudden. Studies on paranoid mutants are one of the major approaches used to investigate signal transduction. Biochemistry of apoptosis points out that the spectrum of enzymes involved in apoptosis of plants is different from animals. Cell signaling is a system that governs basic cellular activities. Cells react to a network of multiple and diverse internal and external signals to decide whether it is time to die or survive. Expression of genes involved in apoptosis, altered cell adhesion, and changed cytoskeleton organization are among those signs of apoptosis that are controlled by the phosphorylation/dephosphorylation of cellular proteins with the combination of two types of enzymes: protein kinases and phosphatases.