RESUMO
The glutathione peroxidase homologous gene (Gpxh gene) in Chlamydomonas reinhardtii is up-regulated under oxidative stress conditions. The Gpxh gene showed a remarkably strong and fast induction by the singlet oxygen-generating photosensitizers neutral red, methylene blue and rose Bengal. The Gpxh mRNA levels strongly increased, albeit much more slowly, upon exposure to the organic hydroperoxides tert-butyl hydroperoxide (t-BOOH) and cumene hydroperoxide. In contrast, the Gpxh mRNA levels were only weakly induced by exposure to the superoxide-generating compound paraquat and by hydrogen peroxide. A comparison of the Gpxh mRNA levels with those of the heat shock protein HSP70A and the iron superoxide dismutase gene showed qualitative and quantitative differences for the three genes under oxidative stress conditions tested. The Gpxh gene is specifically induced by singlet-oxygen photosensitizers and the relative induction by other compounds is much weaker for Gpxh than for the other genes investigated. Using Gpxh promoter fusions with the arylsulfatase reporter gene, we have shown that the Gpxh was transcriptionally up-regulated by singlet-oxygen photosensitizers. It is also shown that the Gpxh promoter contains a region between 104 and 179 bp upstream of the transcription start that is responsible for the mRNA up-regulation upon exposure to 1O2 but not t-BOOH. Within this region a regulatory sequence homologous to the mammalian cAMP response element (CRE) and activator protein 1 (AP-1) binding site was identified within a 16 bp palindrome.
Assuntos
Proteínas de Algas/genética , Chlamydomonas reinhardtii/genética , Glutationa Peroxidase/genética , Oxigênio/farmacologia , Animais , Arilsulfatases/efeitos dos fármacos , Arilsulfatases/genética , Arilsulfatases/metabolismo , Relação Dose-Resposta a Droga , Proteínas de Choque Térmico HSP70/genética , Peróxido de Hidrogênio/farmacologia , Luz , Estresse Oxidativo , Oxigênio/metabolismo , Fármacos Fotossensibilizantes/farmacologia , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/metabolismo , RNA Mensageiro/efeitos da radiação , Proteínas Recombinantes de Fusão/efeitos dos fármacos , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Deleção de Sequência , Oxigênio Singlete , Superóxido Dismutase/genética , Ativação Transcricional/efeitos dos fármacos , Ativação Transcricional/efeitos da radiação , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/efeitos da radiaçãoRESUMO
The photosynthetic single cellular alga Chlamydomonas reinhardtii has been used as a model organism to examine in detail the physiological, biochemical and molecular processes of photosynthesis, flagella synthesis and movement, mineral stress, interactions between nucleus, chloroplasts and mitochondria and other processes. In this review we summarize part of the current knowledge on adaptive responses in C. reinhardtii when it is exposed to oxidative stress and to changes in light intensity, concentration of minerals, herbicides and metals. The individual responses are linked in order to understand the response of the cell, which is continuously subjected to fluctuations, as a whole.
