Abstract
When heterotrophic Euglena gracilis, either dark-grown or exponentially growing, is transferred to autotrophic conditions, the chloroplasts are preferentially induced to develop while cell division is delayed. The nucleic acid extracts from purified isolated chloroplasts were found to contain all the major molecular species such as soluble RNA, DNA, and ribosomal RNA. During the early hours of chloroplast induction under autotrophic conditions, a chloroplast-specific messenger RNA (mRNA), which is not found under continued heterotrophic conditions, is formed. Treatment with streptomycin and 5-fluorouracil, which are known to inhibit chloroplast development, also inhibit the formation of this mRNA. The induction appears to be very similar to the inducible systems described in bacteria and the evidence indicates that chloroplast DNA is the primer for the newly formed mRNA. Streptomycin appears to block the chloroplast development before transcription at DNA level, while 5-fluorouracil blocks through a general interference with RNA metabolism including that of mRNA.
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