Systemic Acquired Resistance.

In the spectrum of plant-microbe interactions disease is a rare outcome. In many interactions complex, integrated defense mechanisms prevent infection and disease. These defensive systems include preformed physical and chemical barriers as well as inducible defenses such as the strengthening of cell walls or synthesis of antimicrobial compounds (i.e., phytoalexins) and proteins.1,2 In certain cases plants react to pathogen attack by developing long-lasting, broad-spectrum systemic resistance to later attacks by pathogens. This phenomenon, termed systemic acquired resistance (SAR), has been observed in many species and may be ubiquitous among higher plants. In the last five years progress has been made toward understanding the molecular basis of SAR. In this review we first provide a brief history of SAR research, then describe our present knowledge of the manifestation and induction of SAR. We discuss recent findings that indicate a central role for the SAR pathway in plant health and finally present our current working model of SAR induction.