Polyacrylamide Gel Analysis of High Molecular Weight Ribonucleic Acid from Etiolated and Green Cucumber Cotyledons

Cucumis sativus L. seeds and 5-day-old dark-grown cotyledons contain 25 and 18 S cytoplasmic ribosomal RNAs as main components. The major increase in nucleic acid content in both green and etiolated cotyledons occurs between days 5 and 7 of germination. This increase is characterized by an important synthesis of 23 and 16 S plastid (chloroplast and proplastid) ribosomal RNAs. Proplastid RNA synthesis appears to continue for a longer period in the dark-grown cotyledons, despite a total RNA content considerably less than in the light-grown cotyledons.The nonribosomal distribution of the chloroplast and proplastid ribosomal RNAs observed in all cases (after extraction and fractionation) results from the lability of the 23 S component. This degradation increases if the chloroplasts and proplastids are isolated prior to extraction of their nucleic acid.