Abstract
Plastid gene expression was analyzed in pea (Pisum sativum L.) plants grown in darkness, continuous far-red light, and white light. Responses induced by continuous far-red light were most likely mediated by PHYA. Plastid transcription activity was low in dark-grown plants. In contrast, plastids of plants grown in white or far-red light showed a 10-fold increase in transcription activity between 4 and 6 d postimbibition (dpi) and a decrease between 6 and 9 dpi. Plastid RNAs accumulated in illuminated plants from 5 to 7 dpi. In far-red-light-illuminated plants, plastid mRNA levels remained elevated until 14 dpi. In white-light-grown plants, most plastid RNAs decreased in abundance after 7 dpi to very low levels by 14 dpi. This indicates that white light induces a general decrease in plastid RNA stability compared to far-red-light-illuminated seedlings. PsbA mRNA accumulated in older, dark-grown, far-red, and white-light-illuminated seedlings, consistent with this RNA having high stability. Transcription of genes encoding the plastid's transcription and translation apparatus increased relative to rbcL and other genes encoding proteins of the photosynthetic apparatus from 4 to 5 dpi and then declined 10-fold from 5 to 9 dpi. These data document dynamic modulation of plastid gene transcription and mRNA stability during light-induced chloroplast development in pea.