Phytochrome‐Induced Appearance of mRNA Activity for the Apoprotein of the Light‐Harvesting Chlorophyll a/b Protein of Barley (Hordeum vulgare)

Abstract

Illumination of dark‐grown barley plants induces a massive insertion of the light‐harvesting chlorophyll u/b protein into the developing thylakoid membrane. Light induces specifically the appearance of mRNA activity for the apoprotein of this chlorophyll‐binding protein [Apel, K. and Kloppstech, K. (1978) Eur. J. Biochem. 85 , 581–588]. This change in mRNA activity can also be induced by a 15‐s red light pulse followed by 4 h darkness. The red light effect is reversed by a subsequent far‐red light treatment. It is concluded that the change in mRNA activity is controlled by phytochrome. In continuous white light the light‐harvesting chlorophyll a/b protein appears within the membrane after a lag period of 4–5 h. This lag period could be partially eliminated by a red light pulse given prior to the onset of continuous illumination. The possible role of the phyto‐ chrome‐induced appearance of mRNA activity as a rate‐limiting step of the greening process is discussed. The light‐harvesting chlorophyll a/b protein could not be detected among the plastid membrane proteins of plants which had been treated with a red light pulse alone. The assembly of the light‐harvesting chlorophyll a/b protein takes place only under continuous illumination which allows chlorophyll synthesis. Thus, the synthesis and ultimate assembly of this chlorophyll‐binding protein depends on the cooperation of two distinct light reactions.