Effect of mitochondrial ascorbic acid synthesis on photosynthesis

• l-galactono-1,4-lactone (l-GalL) increased ascorbate (AA) content in Arabidopsis.
• L-GalL treatment recovered AA content in leaves of the AA-deficient mutant vtc2.
• Mitochondrial activity was not affected by l-GalL treatment.
• l-GalL treatment increased photosynthesis in vtc2 plants, but not in wt plants.
• Leaf stomatal conductance increased in l-GalL treated vtc2 plants.

Ascorbic acid (AA) is synthesized in plant mitochondria through the oxidation of l-galactono-1,4-lactone (l-GalL) and then distributed to different cell compartments. AA-deficient Arabidopsis thaliana mutants (vtc2) and exogenous applications of l-GalL were used to generate plants with different AA content in their leaves. This experimental approach allows determining specific AA-dependent effects on carbon metabolism. No differences in O2 uptake, malic and citric acid and NADH content suggest that AA synthesis or accumulation did not affect mitochondrial activity; however, l-GalL treatment increased CO2 assimilation and photosynthetic electron transport rate in vtc2 (but not wt) leaves demonstrating a stimulation of photosynthesis after l-GalL treatment. Increased CO2 assimilation correlated with increased leaf stomatal conductance observed in l-GalL-treated vtc2 plants.