Incorporation of 32P into ribosomal RNA, transfer RNA and inositol hexaphosphate in germinating pea cotyledons

Abstract 1. 1. RNA synthesis in germinating pea cotyledons has been studied by incorporation of radioactive phosphate. 2. 2. Sucrose density gradient centrifugation of RNA extracts showed that 28-S and 18-S rRNA are synthesized in an approximately linear fashion for up to 6 days. Radioactive label is also incorporated into tRNA. 3. 3. RNA extracts also contained highly labelled low molecular weight material which obscures the tRNA labelling region on sucrose gradients. The labelled material is soluble in 5 % trichloroacetic acid and can therefore be resolved from tRNA. 4. 4. The trichloroacetic acid-soluble material from RNA extracts was labelled very rapidly with 32 P on germination and its labelling approximated to curves for water uptake up to 36 h. This was resolved by DEAE-cellulose chromatography and Sephadex G-25 chromatography into two major components, one of which was impure, being associated with carbohydrate and peptide material. In some preparations the partially purified 32 P-labelled material co-chromatographed with ATP and in others with inorganic phosphate; it is likely that the latter case represented breakdown of ATP. The other rapidly labelled compound was identified as inositol hexaphosphate. 5. 5. 32 P-labelled inositol hexaphosphate was found only in germinating cotyledons and was not detected in the developing embryo tissue.