Chloroplast genomes encode rRNAs, tRNAs, and proteins involved in transcription, translation, and photosynthesis. l h e expression of 15 plastid genes representing each of these functions was quantitated during chloroplast development in barley (Hordeum vulgare). l h e transcription of all plastid genes increased during the initial phase of chloroplast development and then declined during chloroplast maturation. RNAs corresponding to rpoBrpoC1-rpoC2, which encode subunits of a plastid RNA polymerase, and rpsl6, which encodes a ribosomal protein, reached maximal abundance early in chloroplast development prior to genes encoding subunits of the photosynthetic apparatus (rbcl, afp6, psaA, petB). lranscription of rpoB as well as 16s rRNA, trnfM-tmC, and trnK was high early in chloroplast development and declined 10-fold relative to r b c l transcription during chloroplast maturation. RNA hybridizing to psbA and psbD, genes encoding reaction center proteins of photosystem II, was differentially maintained in mature chloroplasts of illuminated barley. Differential accumulation of psbD mRNA relative to r b c l mRNA was due to light-stimulated transcription of psbD. In contrast, enhanced levels of psbA mRNA in mature chloroplasts were due primarily to selective stabilization of the psbA mRNA. These data document dynamic modulation of plastid gene transcription and mRNA stability during barley chloroplast development.

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