TEMPORAL AND SPATIAL PATTERN OF PLASTID GENE-EXPRESSION DURING CRUCIFER SEEDLING DEVELOPMENT AND EMBRYOGENESIS

Several genes which are located close together on mustard (Sinapis alba L.) chloroplast DNA have been found to differ in their temporal mode of expression throughout seedling development. One predominant expression program, exemplified by the psbA gene, is characterized by an early (light-independent) rise in transcript levels, followed by subsequent further accumulation to levels which are much higher in the light than in darkness (development of 'competence' for photocontrol). Other genes located next to the psb A gene show transient or constitutive modes of expression, with no light-dark difference in transcript levels throughout seedling development. The characteristics of light-responsive expression were shown for the nuclear rbcS gene family in Brassica napus L. and Sinapis alba L. cotyledons. The spatial distribution of rbcS and psbA transcripts across sections of crucifer cotyledons appeared to be relatively uniform, but restricted to photosynthetically active cells. Finally, assessment of these transcripts in immature seeds and embryos of Capsella bursa-pastoris has provided in-situ evidence for tissuespecific gene expression during early development © 1990 Springer-Verlag.