What is the Difference Between Systemic Acquired Resistance and Induced Systemic Resistance?

Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR) are two forms of induced resistance in plants that help protect them against pathogens and pests. The main differences between SAR and ISR are the triggers and the mechanisms involved in these resistance responses:

1. Triggers: SAR is induced by plant pathogens, while ISR is triggered by root-colonizing mutualistic microbes, such as Pseudomonas simiae (syn. Pseudomonas fluorescens), Paenibacillus polymyxa, or Trichoderma spp..
2. Mechanisms: SAR often results in an increased level of salicylic acid (SA) and the activation of pathogenesis-related (PR) proteins, such as PR1, PR2, and PR5. It involves one or more long-distance signals that transduce an enhanced immune signal to undamaged plant tissues. In contrast, ISR is commonly regarded as SA-independent and develops without the accumulation of PR proteins.

Both SAR and ISR are systemic responses that enhance the defensive capacity of plants against future pathogen attacks. These responses can be triggered in plants by infection of pathogens, in response to insect herbivory, or upon root colonization by certain rhizosphere mutualistic microbes. The main goal of these resistance responses is to protect plant tissues not exposed to the initial attack against future attacks by pathogens.

Comparative Table: Systemic Acquired Resistance vs Induced Systemic Resistance

Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR) are two major pathways in plant immune mechanisms that help plants fight against infections and stress. Here is a table comparing the differences between the two:

Both SAR and ISR mechanisms operate in plants to protect against invaders such as pathogens and parasites. They also act on the effect of non-expresser of pathogenesis-related genes.