Light-Independent Expression of Three Photosynthetic Genes, cab, rbcS and rbcL, in Coniferous Plants¹

The presence of light-harvesting chlorophyll a/b binding protein (LHCP) and of the small (SSU) and the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase (RuBisCO) was examined in dark- and light-grown seedlings of nine species of coniferous plants. LHCP was present in the dark-grown seedlings of all the species examined, with the exception of Larix kaempferi and Metasequoia glyptostroboides. In the dark-grown seedlings of L. kaempferi, LHCP was not detectable, but RuBisCO was present as the holoenzyme. Although LHCP was not detectable, an appreciable amount of cab transcript was present in the dark-grown seedlings. A protein-labeling experiment suggested the synthesis of LHCP in the dark. LSU was present in the cotyledons of dark-grown seedlings of all the coniferous species examined. The presence of SSU was confirmed in the dark-grown seedlings of the species in Pinaceae and in those of M. glyptostroboides, but not in those of other species. The presence of LSU suggested the presence of SSU because the two are complexed as the holoenzyme even in the etiolated dark-grown seedlings of L. kaempferi. Apparently, the levels of chloroplast proteins in the dark-grown seedlings varied among plant species. However, light-independent expression of the photosynthetic genes seemed to be a general phenomenon in all the coniferous species examined, when it was analyzed at the transcriptional level.