Participates in various redox reactions through the reversible oxidation of the active center dithiol to a disulfide. The F form is known to activate a number of enzymes of the photosynthetic carbon cycle (By similarity). Forms a complex with heterodimeric ferredoxin-thioredoxin reductase (FTR) and ferredoxin. Belongs to the thioredoxin family. Plant F-type subfamily.