The Hypersensitive Reaction in Plants to Pathogens: A Resistance Phenomenon

Both authors have for more than two decades conducted research on a general defense system in plants against pathogens. Our efforts have focused primarily on the induction of this defense system, the hypersensitive reaction (HR), by plant pathogenic bacteria. Nevertheless, it is clear that HR is operative in plants infected by viruses and fungi as well. We propose to describe this phenomenon as it develops across the broad array of host-pathogen interactions. The historical aspects, biochemical-physiological, ultrastuctural and specific genetic factors implicated in the induction and development of HR are defined in some detail. We summarize our understanding of how HR proceeds, based primarily on data from research conducted on bacterial elicitation of the phenomenon. Finally, a number of unsolved basic questions pertinent to the induction and development of HR remain, and these will be delineated.