TRANSCRIPTIONAL CONTROL OF PLASTID GENE-EXPRESSION DURING DEVELOPMENT OF PRIMARY FOLIAGE LEAVES OF BARLEY GROWN UNDER A DAILY LIGHT-DARK REGIME

Plastid DNA transcription was studied during biogenesis and maturation of chloroplasts in primary foliage leaves of barley (Hordeum vulgare L.) seedlings grown under a daily light-dark regime. Specific age-dependent changes in the transcript pattern of plastids have been shown by hybridization to barley plastid DNA fragments of run-on transcript probes derived from homogeneous populations of proplastids and chloroplasts of different age. In proplastids, transcription of the rrn operon is predominant and the increasing transcriptional activity during biogenesis of chloroplasts is mainly the consequence of additional transcription of mRNA and tRNA genes. During maturation of chloroplasts, rrn transcription preferentially decreases and, conversely, transcription of the psbD gene increases. The importance of these changes in plastid DNA transcription is discussed in relation to chloroplast ageing.