The ascorbic acid redox state controls guard cell signaling and stomatal movement

Area of Science:

• Plant physiology
• Biochemistry
• Stress signaling

Background:

• Hydrogen peroxide (H2O2) is a key stress signal in plants, promoting stomatal closure.
• Ascorbate (Asc) is a major antioxidant that neutralizes H2O2.
• Dehydroascorbate reductase (DHAR) enzyme is crucial for maintaining the Ascorbate redox state.

Purpose of the Study:

• To investigate the role of DHAR in regulating guard cell H2O2 levels and stomatal function.
• To determine the impact of altered DHAR expression on plant water loss and drought tolerance.

Main Methods:

• Diurnal monitoring of H2O2 levels and Asc redox state in guard cells and leaves.
• Genetic manipulation of DHAR expression in plants.
• Measurement of stomatal parameters (aperture, conductance) and transpiration rates.
• Assessment of plant water loss and drought tolerance.

Main Results:

• H2O2 levels and Asc redox state exhibit diurnal regulation, with H2O2 increasing and Asc redox state decreasing in the afternoon.
• Increased DHAR expression reduced guard cell H2O2, increased stomatal opening, conductance, and transpiration.
• Elevated Asc redox state in guard cells reduced responsiveness to H2O2 and abscisic acid.
• Plants with increased DHAR showed greater water loss under drought, while suppressed DHAR conferred drought tolerance.

Conclusions:

• DHAR maintains basal Asc recycling in guard cells, which is insufficient to counteract afternoon H2O2 surges, leading to stomatal closure.
• DHAR activity directly influences stomatal aperture and plant water status, highlighting its role in drought response.