Chloroplast development in 4-thiouridine-cultured radish seedlings III. Photochemical activities in isolated plastids

Accumulation of chlorophyll, development of photosystem I andII activities and contents of chloroplastic components wereinvestigated in greening radish seedlings germinated and grownwith 4-thiouridine (4SU). The development of photosystem I activityprior to that of photosystem II was observed also in the 4SU-culturedgreening radish cotyledons in which chlorophyll accumulationwas inhibited up to 60–80% of that of the control. Photochemicalactivities expressed on a plastid protein basis decreased withthe increase of 4SU in the culture medium. In contrast to ferredoxinand ferredoxin-NADP reductase, which were present in significantamounts in the treated cotyledons, chloroplastic cytochromes(f, b₅₅₉ and b₆ decreased in the plastids from 4SU-culturedcotyledons. These results suggest that 4SU interferes in partwith protein synthesis in plastids and thereby with chloroplastdevelopment. (Received December 4, 1979; )