Photo and Nutritional Regulation of the Light-Harvesting Chlorophyll a/b-Binding Protein of Photosystem II mRNA Levels in Euglena

In Euglena gracillis var bacillaris, light exposure increases the level of mRNA encoding the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCPII) approximately twofold. LHCPII mRNA levels increased in the dark upon either malate or ethanol addition. LHCPII mRNA is present but LHCPII is not synthesized in the bleached mutants W₃BUL and W₁₀BSmL, which lack protochlorophyll(ide) and most if not all of the chloroplast genome. Light exposure increased LHCPII mRNA levels in W₃BUL but not in W₁₀BSmL. Carbon availability and light acting through a nonchloroplast photoreceptor appear to regulate LHCPII mRNA levels. A chloroplast photoreceptor and/or a product produced by the chloroplast appear to regulate LHCPII mRNA translation.