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

June 2023 · 4 minute read

The key difference between systemic acquired resistance and induced systemic resistance is that the mode of action of systematic acquired resistance is initiated by salicylic acid, while the mode of action of induced systematic resistance is initiated by jasmonic acid.

Plants have various immunity mechanisms to fight against infections and stress. The plant immune system recognizes pathogen-associated molecular patterns when they are infected with pathogens. Systemic acquired resistance and induced systemic resistance are two major pathways in plant immune mechanisms. These defense mechanisms are triggered by a stimulus before an infection takes place by a pathogen or a parasite.

CONTENTS

1. Overview and Key Difference
2. What is Systemic Acquired Resistance
3. What is Induced Systemic Resistance
4. Similarities – Systemic Acquired Resistance and Induced Systemic Resistance
5. Systemic Acquired Resistance vs Induced Systemic Resistance in Tabular Form
6. Summary – Systemic Acquired Resistance vs Induced Systemic Resistance

What is Systemic Acquired Resistance (SAR)?

Systemic acquired resistance (SAR) is a type of mechanism where an acquired defense confers long-lasting protection against a broad spectrum of microorganisms. SAR requires the molecule salicylic acid (SA) to give out a signal and helps in the accumulation of proteins related to pathogenesis in plants. SA is an essential phytohormone that plays an important role in defense mechanisms.

Systemic Acquired Resistance vs Induced Systemic Resistance in Tabular Form

Figure 01:  Systemic Acquired Resistance

SAR transmits defense signals throughout the plant against secondary infections. It is also involved in the generation and transport of signals through the phloem to the distal tissues that are uninfected. One of the most common components of SA is the methylated derivative of SA. SA biosynthesis takes place through the shikimic acid pathway. This pathway forms two sub-branches called isochorismate synthase (ICS), and phenylalanine ammonia-lyase (PAL) derived pathway. The SA produced by ICS and PAL pathways contributes to the induction and establishment of SAR. The SA signaling that leads to SAR depends on the ankyrin repeat-containing non-expresser of pathogenesis-related genes.

What is Induced Systemic Resistance (ISR)?

Induced systemic resistance (ISR) is a mechanism in plants activated through an infection. The mode of action of ISR does not depend on direct destruction or inhibition of the pathogen but is involved in the increase of the physical or chemical barrier of the host plant.

ISR depends on signal transduction pathways that are activated by jasmonate and ethylene. The defense mechanisms are enhanced through jasmonic acid (JA). JA is formed as a volatile compound to reach plant parts and nearby plants to reduce pathogen attacks and to trigger responses in plant defense. ISR responses mediate by rhizobacteria, and they act effectively against necrotrophic pathogens and insects. Biological factors of ISR include two categories, and they are plant-induced resistance to disease induction or fungi, which promote plant growth, and plant growth-promoting rhizosphere bacteria or plant growth-promoting fungi. They effectively promote plant growth and increase crop yield while increasing the rate of plant resistance to diseases caused by pathogens or pests.

What are the Similarities Between Systemic Acquired Resistance and Induced Systemic Resistance?

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

The mode of action of systematic acquired resistance is initiated by salicylic acid, while the mode of action of induced systematic resistance is initiated by jasmonic acid. Thus, this is the key difference between systemic acquired resistance and induced systemic resistance. Besides, the main function of systemic acquired resistance is to defend against secondary infections acquired by a primary infection, while the main function of induced systemic resistance is to express physical and chemical resistance against pathogens. Moreover, salicylic acid is the main signaling molecule of systemic acquired resistance, while both jasmonic acid and ethylene are involved in the signaling of induced systemic resistance.

The below infographic presents the differences between systemic acquired resistance and induced systemic resistance in tabular form for side-by-side comparison.

Summary – Systemic Acquired Resistance vs Induced Systemic Resistance

Systemic acquired resistance and induced systemic resistance are two major pathways in plant immune mechanisms. These defense mechanisms are triggered by a stimulus before an infection takes place by a pathogen or a parasite. The mode of action in systematic acquired resistance is initiated by salicylic acid, while the mode of action in induced systematic resistance is initiated by jasmonic acid. Systemic acquired resistance is a type of mechanism where an acquired defense confers long-lasting protection against a broad spectrum of microorganisms. Induced systemic resistance is a mechanism in plants activated through an infection. So, this summarizes the difference between systemic acquired resistance and induced systemic resistance.

Reference:

1. Choudhary, Devendra K., et al. “Induced Systemic Resistance (ISR) in Plants: Mechanism of Action.” Indian Journal of Microbiology, vol. 47, no. 4, 2007, pp. 289–297.
2. Gao, Qing-Ming, et al. “Signal Regulators of Systemic Acquired Resistance.” Frontiers in Plant Science, vol. 06, 2015.

Image Courtesy:

1. “Systemic response after pathogen infection” By YumeOmoi – Own work (CC BY-SA 4.0) via Commons Wikimedia

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