In angiosperms, light has been shown to induce the expression of cab and rbcS genes, which encode the apoprotein of lightharvesting 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. a chloroplast, processed to the size of the mature protein, and then assembled as part of the PSII complex or combined with LSU to form the holoenzyme of Rubisco.Although light is generally required for the synthesis of Chl in angiosperms, coniferous plants can produce large amounts of Chl in cotyledons of dark-grown seedlings (15). This phenomenon suggests that the development of chloroplasts can proceed without illumination in conifers. The expression of cab and rbcS is positively regulated by a phytochromemediated response (5,6,11,13,20), but the fact that the cotyledons of dark-grown seedlings of coniferous plants contain chlorophylls suggests that some genes, such as cab and rbcS, are expressed even in darkness. In fact, Alosi et al. (1) recently showed the presence of LHCP and cab transcript in dark-grown Douglas-fir seedlings.In the present study, we examined whether two genes, cab and rbcS, are expressed in the cotyledons of dark-grown pine seedlings. Our results indicate that, even in the dark, the levels of the transcripts increase and the translated products of each gene are accumulated in the course of germination.Light is a modulator of complex developmental and regulatory mechanisms in higher plants. In the past decade, the regulation of gene expression by light has been studied extensively at the molecular level (23). Of the genes whose transcription is regulated by light, the cab2 and rbcS genes are the ones whose regulation has been studied in greatest detail (23). These genes encode the LHCP and the SSU of Rubisco. Products of both genes are synthesized in the cytoplasm as precursor polypeptides of higher molecular masses than the mature functional peptides. 2Abbreviations: cab, nuclear genes encoding LHCP; LHCP, apoprotein of light-harvesting Chl a/b binding protein; Rubisco, ribulose bisphosphate carboxylase/oxygenase; RbcS, nuclear genes encoding the small subunit of Rubisc...