Analysis by the use of polyacrylamide gel electrophoresis was worked out for the comparative studies on chloroplast ribonucleic acids from radish cotyledons grown in the presence and absence of 4-thiouridine, which had been shown to prevent the formation of the functional proteins proper to the chloroplast such as protochlorophyllideholochrome and ribulose 1, 5-diphosphate carboxylase. The rate of de novo biosynthesis of chloroplast ribonucleic acids on illumination in the cotyledons cultured with 4-thiouridine was significantly delayed as compared with that of chloroplast ribonucleic acids from the cotyledons without 4-thiouridine.
On the other hand there was no difference in the formation of ribosomal ribonucleic acids between the 4-thiouridine treated plants and the untreated. The results obtained indicate that 4-thiouridine must have inhibited the development of proplastid (precursor of chloroplast) during the germination stage followed by the growth in the dark.