LIGHT-INDEPENDENT EXPRESSION OF CAB AND RBCS GENES IN DARK-GROWN PINE-SEEDLINGS

In angiosperms, light has been shown to induce the expression of cab and rbcS genes, which encode the apoprotein of light-harvesting chlorophyll a/b binding protein (LHCP) and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), respectively. By contrast, chlorophylls are synthesized in the cotyledons of pine seedlings even if seeds are germinated in the dark. We have examined the expression of cab and rbcS genes in the cotyledons of pine (Pinus thunbergii) seedlings grown in darkness. The proteins of LHCP and the large subunit and the small subunit of Rubisco were detected in the cotyledons of dark-grown seedlings. The transcripts of cab and rbcS genes were present at substantial levels in dark-grown seedlings. However, the transcripts and the translated products of the genes were not found in the embryos of dry seeds. These results indicate that light is not required for the expression of cab and rbcS genes during the course of development of the cotyledons of pine seedlings. The processing of the precursor polypeptides of the mature proteins also appears to take place even in the dark.