Research on the mechanisms of plant defense responses to stress and pathogen attack has attracted much attention in recent years. This increasing interest stems from the fact that the tools of molecular biology now enable us to study the molecular basis of old biological concepts such as host-pathogen recognition (and particularly the gene- for-gene relationship), hypersensitive cell death and systemic acquired resistance. Our knowledge about avirulence and resistance genes, elicitors, signal transduction and genes involved in plant defense is rapidly expanding. Moreover we are just beginning...