[en] σ-Aminolevulinate dehydratase has been found to be activated in vitro by dithiotreitol and factors isolated from radish cotyledons grown under continuous far-red light. Cross experiments, between fructose 1-6 bisphosphatase system, and σ-aminolevulinate dehydratase, show that these factors are functionally identical to thioredoxin f (author)