DIFFERENTIAL TRANSCRIPTION OF PEA CHLOROPLAST GENES DURING LIGHT-INDUCED LEAF DEVELOPMENT TRANSCRIPTION - CONTINUOUS FAR-RED LIGHT ACTIVATES CHLOROPLAST TRANSCRIPTION

Plastid gene expression was analyzed in pea (Pisum sativum L.) plants grown in darkness, continuous far-red light, and white light. Response s induced by continuous far-red light were most likely mediated by PHY A. Plastid transcription activity was low in dark-grown plants. In con trast, plastids of plants grown in white or far-red light showed a 10- fold increase in transcription activity between 4 and 6 d postimbibiti on (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 pl ants, plastid mRNA levels remained elevated until 14 dpi. In white-lig ht-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 t ranscription and translation apparatus increased relative to rbcL and other genes encoding proteins of the photosynthetic apparatus from 4 t o 5 dpi and then declined 10-fold from 5 to 9 dpi. These data document dynamic modulation of plastid gene transcription and mRNA stability d uring; light-induced chloroplast development in pea.