The demand for ascorbate recycling capacity rises as the ascorbate pool size increases in Arabidopsis plants.

Ascorbate recycling is required for high ascorbate accumulation. Hence, when the ascorbate pool size is small, does the demand for ascorbate recycling decrease? We herein investigate the impact of ascorbate recycling capacity on ascorbate pool size in an ascorbate-deficient background. Our findings demonstrate that a smaller ascorbate pool size lowers the need for ascorbate recycling capacity even under light stress.

Chloroplast dehydroascorbate reductase and glutathione cooperatively determine the capacity for ascorbate accumulation under photooxidative stress conditions.

Ascorbate is an indispensable redox buffer essential for plant growth and stress acclimation. Its oxidized form, dehydroascorbate (DHA), undergoes rapid degradation unless it is recycled back into ascorbate by glutathione (GSH)-dependent enzymatic or non-enzymatic reactions, with the enzymatic reactions catalyzed by dehydroascorbate reductases (DHARs). Our recent study utilizing an Arabidopsis quadruple mutant (∆dhar pad2), which lacks all three DHARs (∆dhar) and is deficient in GSH (pad2), has posited that these GSH-dependent reactions operate in a complementary manner, enabling a high accumulation of ascorbate under high-light stress.

Distribution and Functions of Monodehydroascorbate Reductases in Plants: Comprehensive Reverse Genetic Analysis of Enzymes.

Monodehydroascorbate reductase (MDAR) is an enzyme involved in ascorbate recycling. has five genes that encode two cytosolic, one cytosolic/peroxisomal, one peroxisomal membrane-attached, and one chloroplastic/mitochondrial isoform. In contrast, tomato plants possess only three enzymes, lacking the cytosol-specific enzymes.