Dehydroascorbate Reductases and Glutathione Set a Threshold for High-Light-Induced Ascorbate Accumulation

Area of Science:

• Plant Physiology
• Biochemistry
• Molecular Biology

Background:

• Ascorbate is vital for plant survival, acting as a redox buffer, especially under high light stress.
• Dehydroascorbate reductases (DHARs) facilitate ascorbate recycling using reduced glutathione (GSH).
• Previous studies showed conflicting results regarding DHARs' role in ascorbate recycling under stress.

Purpose of the Study:

• To investigate the function of DHARs in ascorbate accumulation and recycling in *Arabidopsis thaliana*.
• To determine the interplay between DHAR activity, GSH levels, and high-light-induced ascorbate accumulation.

Main Methods:

• Generated *Arabidopsis* mutants: a triple *dhar* mutant (∆dhar) and a quadruple mutant (∆dhar vtc2).
• Assessed ascorbate levels in wild-type and mutant plants under varying light conditions.
• Utilized the *pad2* mutant (reduced GSH levels) to study the combined effects of DHAR deficiency and low GSH.

Main Results:

• DHARs contribute to full ascorbate accumulation under high light but are dispensable at moderate levels.
• Plants lacking DHARs and having reduced GSH (∆dhar *pad2*) showed severely inhibited high-light ascorbate accumulation.
• Ascorbate degradation product, threonate, increased significantly in the ∆dhar *pad2* mutant, indicating limited recycling capacity.

Conclusions:

• DHAR activity and GSH content are critical determinants of ascorbate recycling capacity.
• Both DHARs and sufficient GSH are essential for maintaining ascorbate homeostasis under high light stress.
• These factors collectively establish a threshold for high-light-induced ascorbate accumulation in plants.