White Light Effects on the mRNA for the Light-Harvesting Chlorophyll a/b-Protein in Lemna gibba L. G-3.
Translation products of poly(A) mRNA isolated from Lemna gibba L. G-3 include a major polypeptide of 32,000 daltons which is immunoprecipitated by antiserum to chlorophyll a/b-protein from Chlamydomonas. This 32,000 dalton polypeptide represents a precursor to the light-harvesting chlorophyll a/b-protein of molecular weight 28,000 found in the thylakoid membranes of Lemna gibba. The amount of this translatable mRNA decreases relative to other translatable mRNAs when green plants grown in continuous white light are placed in darkness. This decrease occurs rapidly. The most rapid decline occurs during the first day; after 4 days of darkness, only a low level of this mRNA can be detected by in vitro translation. When the plants are returned to white light there is an increase in the relative level of this mRNA which can be easily detected within two hours. The in vivo synthesis of this protein has been assayed under the different light conditions. The light effects on the in vivo synthesis of the chlorophyll a/b-protein reflect the light effects on the translatable mRNA for the polypeptide. The results indicate that light induced changes in the synthesis, processing, or degradation of chlorophyll a/b-protein mRNA could account for the light-induced changes observed in the effective synthesis rates for the chlorophyll a/b-protein in vivo.
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Biology Department and Molecular Biology Institute, University of California, Los Angeles, California 90024.