title: Photosensitizers neutral red (type I) and rose bengal (type II) cause light-dependent toxicity in Chlamydomonas reinhardtii and induce the Gpxh gene via increased singlet oxygen formation.
abstract: The connection between the mode of toxic action and the genetic response caused by the type I photosensitizer and photosynthesis inhibitor neutral red (NR) and the type II photosensitizer rose bengal (RB) was investigated in the green alga Chlamydomonas reinhardtii. For both photosensitizers, a light intensity-dependent increase in toxicity and expression of the glutathione peroxidase homologous gene (Gpxh) was found. The toxicity of RB was reduced by the singlet oxygen (1O2) quenchers 1,4-diazabicyclo[2.2.2]octane and L-histidine, and the RB-induced Gpxh expression was stimulated in deuterium oxide-supplemented growth medium. These observations clearly indicate the involvement of 1O2 in both toxicity and the genetic response caused by RB. NR up-regulated the expression of typical oxidative and general stress response genes, probably by a type I mechanism, and also strongly induced the Gpxh expression. The stimulating effect of deuterium oxide in the growth medium suggested the involvement of 1O2 also in the NR-induced response. Indeed, an increased 1O2 formation was detected with EPR-spin trapping in NR-treated spinach thylakoids. However, none of the 102 quenchers could reduce the light-dependent toxicity of NR in C. reinhardtii, indicating that NR has a different mode of toxic action than RB.
authors.affiliation: Department of Environmental Microbiology and Molecular Ecotoxicology, Swiss Federal Institute for Environmental Science and Technology (EAWAG), Ueberlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Beat B
authors.initials: BB
authors.lastname: Fischer
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.forename: Rik L
authors.initials: RL
authors.lastname: Eggen
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005786:Gene Expression Regulation / Q000187:drug effects; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D008027:Light; D009499:Neutral Red / Q000378:metabolism / Q000633:toxicity*; D018384:Oxidative Stress / Q000235:genetics / Q000528:radiation effects; D017319:Photosensitizing Agents / Q000633:toxicity*; D010879:Piperazines / Q000378:metabolism; D012395:Rose Bengal / Q000378:metabolism / Q000633:toxicity*; D026082:Singlet Oxygen / Q000378:metabolism* / Q000528:radiation effects; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000528:radiation effects
chemical_list: D017319:Photosensitizing Agents; D010879:Piperazines; D026082:Singlet Oxygen; D012395:Rose Bengal; D009499:Neutral Red; D006639:Histidine; D005979:Glutathione Peroxidase; C007306:triethylenediamine