Poster: Oxidative Stress
Abs #
145: Acclimation to oxidative stress in Chlamydomonas
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Presenter: |
Ledford, Heidi K., hledford@nature.berkeley.edu |
Authors | Ledford, Heidi K. (A) Huang, Shih-Yau (A) Chin, Brian (A) Niyogi, Krishna K. (A) | | Affiliations: |
(A): University of California, Berkeley
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The ability to respond to changes in oxidative load is an absolute requirement for survival in an aerobic environment. Previous studies have shown the importance of redox poising for the proper regulation of oxidative stress responses in plants, yet little is known about how plant cells sense and respond to perturbations in cellular redox state.
We are investigating the regulation of oxidative stress responses in the model alga Chlamydomonas reinhardtii. In contrast to E. coli and S. cerevisiae, Chlamydomonas does not exhibit a strong acclimation response to hydrogen peroxide. Instead, we have found that pretreatment with nonlethal doses of rose bengal or neutral red (photosensitizing dyes that produce singlet oxygen upon exposure to light) results in the transient activation of defense responses, enabling pretreated cells to survive subsequent exposure to otherwise lethal levels of the dye. Pretreatment with rose bengal only confers protection when administered in the light, suggesting that activation of defense responses is dependent upon the production of low levels of singlet oxygen. Acclimation to singlet oxygen does not involve changes in carotenoid or tocopherol concentrations, but is dependent upon transcription and de novo protein synthesis. Microarray analysis of RNA levels for ~2900 genes indicates that expression of the antioxidant enzyme glutathione peroxidase is strongly induced during exposure to rose bengal, as is a putative sigma-class glutathione S-transferase. To isolate regulatory components involved in acclimation, we have screened an EMS-mutagenized population for mutants that fail to acclimate. Characterization of these mutants may clarify the mechanisms by which singlet oxygen stress responses are regulated in photosynthetic organisms.
