The light‐dependent accumulation of the P700 chlorophyll a protein of the photosystem I reaction center in barley: Evidence for translational control

Abstract

The light‐dependent accumulation of the P700 chlorophyll a protein of the photosystem I reaction center has been studied in greening barley (Hordeum vulgare L.) seedlings. Immunoblot analysis of total cellular protein fractions and immunogold labelling of the P700 chlorophyll a protein in ultrathin sections of Lowicryl‐embedded leaf tissue revealed that the concentration of this chlorophyll‐binding protein in plastids of dark‐grown barley seedlings is below the limit of detection. Upon illumination with white light, a rapid accumulation of this protein is induced. This light effect seems not to be regulated at the level of transcription. The gene for the P700 chlorophyll a protein has been mapped within the large single‐copy region of the plastid DNA of barley. High levels of transcripts of this gene are present already in dark‐grown seedlings and remain fairly constant throughout an extended illumination period. Polysomes were isolated from etioplasts and chloroplasts. The same high relative concentration of mRNA encoding the P700 chlorophyll a protein was present in both polysome fractions. This result suggests that the light‐dependent accumulation of the P700 chlorophyll a protein during chloroplast formation in barley seedlings is regulated at the translational, or posttranslational, level. Copyright © 1986, Wiley Blackwell. All rights reserved