Benzothiadiazole-induced resistance modulates ozone tolerance

Area of Science:

• Plant Physiology
• Environmental Stress Biology
• Biochemistry

Background:

• Ozone (O3) is a major air pollutant causing significant phytotoxicity.
• Benzothiadiazole (BTH) is a plant activator that can induce systemic acquired resistance (SAR).
• The timing of BTH application relative to O3 exposure influences plant responses.

Purpose of the Study:

• To investigate the impact of BTH pretreatment timing on bean plant susceptibility to acute ozone fumigation.
• To elucidate the underlying biochemical mechanisms, including hydrogen peroxide (H2O2) levels and antioxidant enzyme activities.

Main Methods:

• Bean plants were pretreated with BTH at different intervals (1-2 days or 5-7 days) before acute ozone fumigation (200 nL/L for 4 h).
• Plant damage, cell death, and hydrogen peroxide localization were assessed.
• Biochemical assays measured ascorbate (AA) levels and ascorbate peroxidase (APX) and guaiacol peroxidase (GuPX) activities.

Main Results:

• Early BTH pretreatment (1-2 days) increased bean plant susceptibility to O3, leading to rapid cell death correlated with H2O2 accumulation.
• Late BTH pretreatment (5-7 days) conferred tolerance to O3, with no visible damage or H2O2 accumulation observed.
• Late BTH pretreatment led to increased ascorbate levels and altered peroxidase activities (decreased APX, increased GuPX), suggesting enhanced antioxidant defense.

Conclusions:

• The timing of BTH application critically determines its effect on O3 tolerance in bean plants.
• Early BTH treatment may prime plants for hypersensitive responses, while later treatment allows for the development of robust antioxidant defenses.
• Increased guaiacol peroxidase activity and ascorbate levels in later-treated plants likely contribute to O3 tolerance by mitigating oxidative damage.