Molecular effects of some stress factors on the chloroplast genetic apparatus of the flagellate Euglena gracilis

The chloroplast system of the flagellate Euglena gracilis is particularly s ensitive to various chemical and physical factors. Ofloxacin, a quinolone a ntibacterial chemotherapeutical, the mutagen nitrosoguanidine, as well as t he hyperthermic cultivation at 33 degrees C for 7 days, induce complete ble aching of Euglena cultures. Treatment with all those factors results in a m ass degradation of E. gracilis chloroplast DNA. Significant decrease in the hybridisation signal intensity is connected with prolongation of cell expo sure to the stress factors. No evidence for chloroplast genome rearrangemen t was obtained for chloroplasts of chemically stressed cells. On the contra ry, heat induced loss of chloroplast functions is associated with partial r estructurations of the chloroplast genome. Electrophoretograms of E. gracil is total RNA show distinct difference between wild type cells and bleached mutants. Bands for 23S and 16S rRNA are absent in all mutants. Subsequent h ybridisation with DNA probes for nuclear encoded chloroplast proteins as Ru bisco SSU and LHCPII provided identical signals for wild type cells and all mutants. However, in the case of the petJ gene for cytochrome cs variable hybridisation signals were obtained with northern blots from an ofloxacin-b leached mutant depending on the light regime.