Thiol-disulfide oxidoreductase that poorly activates chloroplastic malate dehydrogenase (NADP-MDH) and fructose-1,6-bisphosphatase. Provides reducing equivalents for peroxiredoxin Q. Expressed in leaves. Expression decreases in developing seeds and increases during seed germination. By light in leaves. Belongs to the thioredoxin family. Plant Y-type subfamily.