The Role of Salicylic Acid in Systemic Acquired Resistance Signaling Pathways

Salicylic acid (SA) is an important endogenous compound in plant signaling pathways. Exogenous SA can induce expression of plant defense genes and lead to a degree of protection against plant pathogens. Increases in endogenous SA levels correlates with expression of defense genes and development of pathogen resistance,indicating that SA is required in the expession of systemic acquired resistance (SAR) but is not the only factor. SAR expression results from joint action of SA and other compounds. SAR induces the plant to generate a signal at the site of infection,and this signal can then be translocated systemically to the entire plant by a signal transmitting compound. SA may be serving as the signal transmitter,although the chemical nature and molecular mechanism of the signal transmitter still lacks experimental evidence.