Formation of Large Thioredoxin / Accompanies Chloroplast Development in Scenedesmus obliquus

Chloroplast-free mutant cells C-2A ' of the green algae Scenedesmus obliquus lack thioredoxin / , which functions in the light activation of chloroplast enzymes, but do con­ tain the regular thioredoxins I and II. When dark-grown algae are transferred to light, thioredoxin / activity appears rapidly and increases in parallel with photosynthetic ac­ tivities; however it precedes chlorophyll biosynthesis. The formation o f thioredoxin / is inhibited by cycloheximide indicating that it occurs on the cytoplasmic ribosom es, in accord with the lack of thioredoxin genes on the chloroplast genom es.