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Systemic acquired resistance

Uwe Conrath. Plant Signal Behav. 2006 Jul.

Abstract

Upon infection with necrotizing pathogens many plants develop an enhanced resistance to further pathogen attack also in the uninoculated organs. This type of enhanced resistance is referred to as systemic acquired resistance (SAR). In the SAR state, plants are primed (sensitized) to more quickly and more effectively activate defense responses the second time they encounter pathogen attack. Since SAR depends on the ability to access past experience, acquired disease resistance is a paradigm for the existence of a form of "plant memory". Although the phenomenon has been known since the beginning of the 20th century, major progress in the understanding of SAR was made over the past sixteen years. This review covers the current knowledge of molecular, biochemical and physiological mechanisms that are associated with SAR.

Keywords: 2,6-dichloroisonicotinic acid; Arabidopsis; MAP kinase; benzothiadiazole; defense response potentiation; elicitor; parsley cell culture; priming; salicylic acid; sensitization.

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Figures

Figure 1

Figure 1

Sequence of events associated with the establishment of SAR. Upon primary infection of a plant leaf with a necrotizing pathogen, a yet unknown systemic signal(s) is distributed systemically throughout the plant. The signal causes systemic accumulation of salicylic acid (SA). SA causes direct activation of SAR genes, some of which encode enzymes with antimicrobial activity. SA also conveys the tissue to the primed state which is characterized by an enhanced capacity to activate defense responses upon secondary pathogen attack. The faster and/or stronger activation of defense responses at the sites of secondary infection results in a decrease in disease symptoms, reflecting the SAR state.

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