ABSTRACT
The assessment of genotoxic potential in surface water requires test methods, among which are those that detect initial DNA damage in organisms of aquatic biocenosis. The microgel electrophoresis (MGE) "comet assay" was applied to a ubiquitous unicellular green alga (Chlamydomonas reinhardtii) to detect DNA damage caused by genotoxins. For this, the test protocol described by Singh NP et al. [Exp Cell Res 175: 184-191, 1988] was modified. Major modifications were the use of alkaline lysis buffer with ionic detergents and the reduction of preincubation and electrophoresis times. Short-time exposure of Chlamydomonas to the well-known genotoxicants 4-nitroquinoline-1-oxide (4-NQO), N-nitrosodimethylamine, and hydrogen peroxide led to dose-dependent DNA damage. Chlamydomonas responded very sensitively to treatment with increasing doses of 4-NQO. At a concentration of 25 nM, significant DNA damage was observed. At higher 4-NQO doses (> 100 nM), DNA damage was visible as complete DNA fragmentation into fine granules. N-Nitrosodimethylamine caused genotoxic effects at a concentration range from 0.014 to 0.14 mM without producing complete DNA fragmentation at the concentrations tested (highest dose, 140 mM). To evaluate the influence of illumination conditions during exposure, cells were incubated with increasing doses of H2O2 (0.25-1.0 mM) in darkness and in light. Our results indicate that incubation in light enables Chlamydomonas to cope with oxidative stress more efficiently than under dark conditions. To a certain extent, cytotoxic as well as genotoxic effects of H2O2 depend on the illumination condition or repair and anti-oxidative protection mechanisms activated by light, respectively.
Subject(s)
4-Nitroquinoline-1-oxide/toxicity , Chlamydomonas reinhardtii/drug effects , DNA Damage , DNA/drug effects , Dimethylnitrosamine/toxicity , Hydrogen Peroxide/toxicity , Water Pollutants, Chemical/toxicity , Animals , Cell Nucleus/drug effects , Cell Nucleus/ultrastructure , Chlamydomonas reinhardtii/genetics , Chlamydomonas reinhardtii/ultrastructure , DNA, Protozoan/drug effects , ElectrophoresisABSTRACT
Fossil-fueled power plants typically operate below their design capacities for a large fraction of their service life. In the United States, increased fuel and capital costs attributable to this off-design operation are considerable. This article describes the reasons for off-design operation and its importance in designing and selecting new power plants. Recent studies of coal gasification combined-cycle power plants show how computer simulations of off-design performance can aid in the design process, and they suggest that such simulations can be useful in reducing the cost of building and operating new power plants.
