| Dark-grown Euglena gracilis Z were exposed to white light which induces chloroplast development including a massive formation of thylakoid membranes and carbon dioxide-fixing enzyme RuBPCase. Results showed both nuclear and plastid gene expression are differentially regulated during chloroplast development. The comparison of the fold-increase between mRNA and protein suggests a strong post-transcriptional control on LSU gene expression. Expression of CP I and 26 kd and 28 kd LHCP genes appears subject to control in the nucleus up to 1 day. After this, post-transcriptional control appears to be important. The level of CP a (58 kd) apoprotein is regulated by its mRNA throughout greening. The protein turnover of both of subunits of RuBPCase and all of the apoproteins of CP complexes showed drastic turnover in the dark-grown cells compared to light-exposed cells, suggesting that post-translational control is the main regulation mechanism on these proteins in the dark-grown cells. Accumulation kinetics of CFo-III subunit of ATPase suggests two waves of synthesis and insertion of this polypeptide into the thylakoid membranes during chloroplast development. Overall, light-induced regulation of the proteins shows that (1) the accumulation of different plastid proteins is subject to different controls, (2) the multiple controls, either overlapping or invoked at specific times, may regulate the synthesis of any one plastid protein during light-induced chloroplast development in Euglena. |
