Comparison of the action of light on ribosomal RNA synthesis in cabbage and mustard seedlings

We have compared the action of light on ribosomal RNA synthesis in mustard and cabbage seedlings, two of the most frequently used systems for the studies of anthocyanin synthesis. The level of RNA (both t-RNA and r-RNA) "stored" in mustard dry seeds is much lower than in cabbage dry seeds. The kinetics of RNA synthesis in cabbage and mustard seedlings exposed to light are very different: In cabbage seedlings, light produces no apparent stimulation of cytoplasmic r-RNA synthesis, while it does increase plastid r-RNA synthesis. On the other hand, in mustard seedlings, light promotes both cytoplasmic and plastid ribosomal RNA synthesis. Streptomycin, which inhibits chlorophyll formation and chloroplast development while having no effect (mustard) or enhancing (cabbage) anthocyanin synthesis in these two systems, is in both cases an effective inhibitor of plastid r-RNA synthesis, but not of cytoplasmic r-RNA synthesis.