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Twenty-three species belonging to the class Euglenophyceae were recorded from the Museum Lake, Thiruvananthapuram, India. A canonical correspondence analysis (CCA) between environmental variables and the dominant euglenophytes indicated interaction with certain physical and chemical parameters, in particular rainfall, electrical conductivity and phosphate versus their distribution in the Museum Lake. The dominant species were Euglena deses, Trachelomonas hispida and Trachelomonas volvocina . The CCA results indicate interaction between a variety of environmental parameters and species abundance. A closer examination suggests some external factor (e.g. evaporation) affecting water quality rather than the environment changing the algal biomass. With low rainfall the phosphate concentration increased from 1.5 to 6.9 mg P/l (likely as a result of anoxic conditions in the muddy bottom) and simultaneously nitrate was (partly) taken up by these dominant algae, as a result of which N : P ratios decreased from 4.5 to 0.7. The present study shows that the dominant euglenoid species co-occur in relatively hard water with high phosphorus concentration, and can be considered as useful bio-indicators in assessing the health and extent of deterioration of a lake ecosystem.

The enzyme superoxide dismutase (SOD) holds a key position in the microalgal antioxidant network. The present research focused on oxidative stress responses in the Antarctic diatom Chaetoceros brevis F. Schutt during transition to excess (including ultra- violet radiation (UVR)) and limiting irradiance con- ditions. Over a 4 d period, cellular responses of thiobarbituric acid reactive substances (TBARS, a general oxidative stress indicator), SOD activity, photosynthetic and xanthophyll cycle pigments, PSII efficiency, and growth were determined. In addition, oxidative responses were measured during a daily cycle. Changing irradiance conditions significantly affected growth rates of C. brevis. PSII efficiency decreased significantly during periodic excess irradi- ance and increased under low irradiance conditions. Transition to excess irradiance increased the ratio of xanthophyll to light-harvesting pigments, whereas the opposite was observed for cultures transferred to low irradiance. This acclimation process was com- pleted after 2 d in the new irradiance environment. SOD activity increased significantly after the first day regardless of the new irradiance environment but returned to preexposure values on the fourth day. We hypothesize that SOD activity may be tem- porarily elevated in C. brevis after irradiance shifts, thereby reducing oxidative stress when photoaccli- mation is in progress.

Antioxidant enzymes such as superoxide dismutase (SOD) play a key role in the removal of reactive oxygen species produced during visible and ultraviolet irradiance stress in microalgae and plants. However, little is known about the enzymatic antioxidative stress responses in ecologically important Antarctic marine microalgae. SOD in particular is difficult to analyze, possibly due to problems in obtaining sufficient quantities necessary for reliable and reproducible enzymatic assays. The aim of the present work was to create a sensitive, easy-to-use and reliable method for SOD determination in Antarctic microalgal material by comparing and optimizing existing protein extraction procedures and SOD assays in the marine Antarctic diatom Chaetoceros brevis. Optimization was achieved in cell disruption (sonication) and protein extraction procedures, extraction buffers, SOD assay methods (xanthine/xanthine oxidase and NBT/ riboflavin photometric quantitative methods and native gel electrophoresis qualitative method) and the assay temperature. Protein extraction was optimal at low sonication amplitudes after a few pulses, irrespective of the type of buffer used. Extraction efficiency varied highly between the tested buffers; most protein was extracted in the presence of 1% of Triton X-100. SOD activity was best quantified using the NBT/riboflavin method in combination with a buffer containing potassium phosphate and Triton X-100. Moreover, the NBT/ riboflavin method was demonstrated to be the most reliable and sensitive method at low temperatures (5 degrees C). (c) 2007 Elsevier B.V. All rights reserved.

Enteromorpha prolifera (Scheldt Estuary) and E. linza (Thermaikos Gulf) were incubated at three salinities with 100 and 200 µg L-1Cd and Zn. The objective was to measure effects of Cd, Zn and nitrogen (N) status on the pools of metal-binding non-protein thiols: glutathione and phytochelatins, (?-glutamyl-cysteinyl)n-glycine (PC). In E. linza, ammonium pools were higher, but amino acid pools, total N and protein contents were lower than in E. prolifera. Reduced glutathione (GSH) pools were positively correlated with free glutamate and protein contents. In E. linza GSH pools increased and the ratio of reduced to oxidized glutathione (GSH:(GSH + 0.5GSSG)), an indicator of oxidative stress, decreased with Cd contents, indicating Cd-induced glutathione oxidation. Total glutathione pools (reduced plus oxidized) ranged from 16 nmol S gdwt-1 in controls (at 0.5 µmol Cd gdwt-1) to 179 nmol S gdwt-1 (at 1.9 µmol Cd gdwt-1) at the highest cadmium dosage. Cadmium stimulated PC synthesis in E. prolifera which suggests that in N-rich algae, glutathione pools were high enough for PC synthesis. In both species GSH and protein increased with Zn contents, whereas GSH:(GSH + 0.5GSSG) decreased, which would indicate Zn-induced oxidative stress; in E. linza, at the highest salinity the glutathione redox ratio decreased from 0.61 (at 2.9 µmol Zn gdwt-1) to 0.26 (at 4.9 nmol S gdwt-1) (at 0.5 mol Cd gdwt-1). PCs were not synthesized in response to Zn, which may have resulted in Zn-induced GSH oxidation. The presence of both oxidative effects (Cd, Zn) and detoxification (Cd) could be identified by observing the responses of glutathione and PC pools to metal stress. [KEYWORDS: Cadmium ; Enteromorpha ; Glutathione ; Macroalgae ; Phytochelatins ; Zinc]

Short-term photosensitivity and oxidative stress responses were compared for three groups of marine microalgae: Antarctic microalgae, temperate diatoms and temperate flagellates. In total, 15 low-light-acclimated species were exposed to simulated surface irradiance including ultraviolet radiation (SSI). Photosensitivity was assessed as the rate of recovery of Fv/Fm in the hours following SSI treatment. Before, during and after the SSI treatment, oxidative stress responses were assessed by following xanthophyll content and cycling, and activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase, and glutathione redox status. When acclimated to low irradiance, antioxidant levels were not group specific. Superoxide dismutase activity was positively correlated with cell size, whereas in general, ascorbate peroxidase activity appeared to be lower and glutathione redox status appeared to be higher in the Antarctic than in the temperate species. After SSI exposure, the strong inhibition of PSII was followed by variable rates of recovery, although four species remained photosynthetically inactive. SSI tolerance appeared unrelated to geographic or taxonomic background, or to cell size. PSII recovery was enhanced in species with decreasing superoxide dismutase activity, glutathione redox status and increased xanthophyll cycle activity. We conclude that antioxidant responses are highly species specific and not related to the geographic or taxonomic background. Furthermore, xanthophyll cycling seems more important than antioxidants. Finally, it can be hypothesized that glutathione could function as a stress sensor and response regulator.