Control by Phytochrome of Cytoplasmic Precursor rRNA Synthesis in the Cotyledons of Mustard Seedlings

Publisher Website
Google Scholar
Abstract
The influence of phytochrome (high irradiance reaction; operationally, continuous far red light [FR]) on the incorporation of [3H]uridine into the cytoplasmic 2.5 megadalton precursor rRNA in the cotyledons of mustard (S. alba L.) seedlings was investigated. After irradiating 36 h old etiolated seedlings with 12 h of FR, the rate of incorporation is stimulated .apprx. 2-fold, leading to 50% labeling of the precursor rRNA pool .apprx. 15 min after the tracer has reached the nucleotide precursor pool. In the dark control, there is a significantly smaller pool of precursor rRNA which is half-saturated with label only after .apprx. 27 min. Since neither the specific radioactivity of the UTP pool nor the processing of the precursor rRNA demonstrate a corresponding light-dependent change, phytochrome must mediate an increase of the transcription of the rRNA genes. This gene activation accounts for the increased accumulation of mature cytoplasmic rRNA during the course of photomorphogenesis of the cotyledons.