Blue light-dependent regulation of cytoplasmic ribosomal RNA synthesis in Chlorella

Effect of blue and red light on ribosomal RNA synthesis in autotrophic synchronous cultures of Chlorella pyrenoidosa (strain 211-8b) is studied by pulse labeling experiments with tritiated guanosine. Nucleic acids were separated by electrophoresis on polyacrylamide gels. Compared with darkness and red light (679 nm), blue light (457 nm) of equal quantum flux (0.5-5x10(-10) Einstein cm-2 s-1) stimulates incorporation into ribosomal RNA. This blue light effect is observed in the cytoplasmic ribosomal RNA after 5 min of illumination, whereas the stimulation of chloroplast ribosomal RNA synthesis by blue light appears later. Maturation of chloroplast ribosomal RNA is slower than that of cytoplasmic ribosomal RNA. The blue light effect on the cytoplasmic ribosomal RNA formation does not require chloroplast RNA or protein synthesis as shown by inhibitor studies with rifampicin or lincomycin. The blocking of cytoplasmic protein synthesis by cycloheximide inhibits the blue light effect on ribosomal RNA formation. It is concluded that the cytoplasmic ribosomal RNA transcription is controlled by a blue light sensitive system.