The effect of the DNA hypermethylating 3′-azido-3′-deoxythymidine (AZT) on plastidogenesis was investigated on asynchronous, etiolated Euglena gracilis exposed to continuous light for 72 h. Based on (i) fluorescence and electron microscope aspects of the plastids, (ii) cytochemical localizations of functional PSI and PSII, (iii) immunolocalization of LHCII apoproteins, and (iv) spectrophotometric and HPLC analyses of the photosynthetic pigments, it was found that AZT, at a dose of 5 μM, which does not encroach on cell viability and only slightly interferes with cell proliferation, causes profound alterations of plastids in 10 - 15 % of the cells, without apparently affecting the rest of the cell population. Proplastid-to-chloroplast transformation slowed in this cell sub-population and occurred without the normal co-regulation that characterizes the process in wild type Euglena. In particular, thylakoid assembly was partially prevented while building materials continued to be synthesized and accumulated in the stroma. Chlorophylls were over-synthesized, while carotenoids, phaeophytin and phylloquinone dramatically diminished. The assemblage of PSI and PSII was inhibited. The external envelopes and thylakoid membranes were frequently damaged. Plastids, whose total volume increased with respect to the controls, were often malformed and interconnected. Their fluorescence under UV light declined quickly. The fact that AZT acts specifically at the plastid level, causing effects that are greatly opposed to those previously observed in the alga treated with the DNA demethylating 5-azacytidine, points to a relationship between DNA methylation and plastid differentiation in Euglena.
De-regulation of light-induced plastidogenesis in etiolated Euglena gracilis Klebs treated with DNA hypermethylating 3'-azido-3'-deoxythymidine.
PANCALDI, Simonetta;BONORA, Angelo;BALDISSEROTTO, Costanza;NERI, Luca Maria;FASULO, Maria Palmira
2001
Abstract
The effect of the DNA hypermethylating 3′-azido-3′-deoxythymidine (AZT) on plastidogenesis was investigated on asynchronous, etiolated Euglena gracilis exposed to continuous light for 72 h. Based on (i) fluorescence and electron microscope aspects of the plastids, (ii) cytochemical localizations of functional PSI and PSII, (iii) immunolocalization of LHCII apoproteins, and (iv) spectrophotometric and HPLC analyses of the photosynthetic pigments, it was found that AZT, at a dose of 5 μM, which does not encroach on cell viability and only slightly interferes with cell proliferation, causes profound alterations of plastids in 10 - 15 % of the cells, without apparently affecting the rest of the cell population. Proplastid-to-chloroplast transformation slowed in this cell sub-population and occurred without the normal co-regulation that characterizes the process in wild type Euglena. In particular, thylakoid assembly was partially prevented while building materials continued to be synthesized and accumulated in the stroma. Chlorophylls were over-synthesized, while carotenoids, phaeophytin and phylloquinone dramatically diminished. The assemblage of PSI and PSII was inhibited. The external envelopes and thylakoid membranes were frequently damaged. Plastids, whose total volume increased with respect to the controls, were often malformed and interconnected. Their fluorescence under UV light declined quickly. The fact that AZT acts specifically at the plastid level, causing effects that are greatly opposed to those previously observed in the alga treated with the DNA demethylating 5-azacytidine, points to a relationship between DNA methylation and plastid differentiation in Euglena.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
