温度和紫外辐射胁迫对西藏飞蝗抗氧化系统的影响

为探讨西藏飞蝗(Locusta migratoria tibetensis Chen)对环境的适应机制,报道了温度和紫外辐射胁迫对西藏飞蝗抗氧化系统影响。以西藏飞蝗成虫为试材,研究5—20℃低温、30—45℃高温胁迫和紫外线辐射对其抗氧化酶活性和膜脂过氧化物丙二醛(MDA)含量的影响。在5—20℃低温胁迫下,成虫体壁和消化道超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性及丙二醛(MDA)含量分别随温度降低而升高;在30—35℃高温胁迫下,成虫SOD、POD和CAT活性分别随温度升高而升高,当温度超过35℃时,3种氧化酶活性均下降。长波紫外辐射(UV-A)和中波紫外辐射(UV-B)对处理后24h和72h成虫的SOD活性的影响大于可见光,在UV-A、UV-B和可见光3种光波长处理下,成虫的POD和CAT活性随光照时间的延长而增加,其中UV-B对两种酶活性影响大于UV-A和可见光,表现为UV-B处理组>UV-A处理组>可见光处理组;UV-A和UV-B处理能导致虫体体壁MDA含量明显升高,且对脂质过氧化的诱导存在时间效应;雌虫体壁、雌虫消化道、雄虫体壁和雄虫消化道的MDA含量分别在UV-B72h、UV-A72h、UV-A72h和UV-B72h达最大值0.72、0.88、0.66和0.94 nmol/g鲜重。在20—5℃低温胁迫下,西藏飞蝗成虫抗氧化酶活性升高,能较好的保护自身免遭活性氧自由基的伤害;西藏飞蝗对高温忍耐力差,在高于35℃高温胁迫下,成虫SOD、POD、CAT活性均下降;在长波和中波紫外辐射下,西藏飞蝗抗氧化酶活性显著升高,是西藏飞蝗对紫外线辐射强度大的青藏高原的一种重要适应。     

Countermeasures against space radiation induced oxidative stress in mice

Of particular concern for the health of astronauts during space travel is radiation from protons and high atomic number (Z), high energy particles (HZE particles). Space radiation is known to induce oxidative stress in astronauts after extended space flight. In the present study, the total antioxidant status was used as a biomarker to evaluate oxidative stress induced by proton and HZE particle radiation in the plasma of CBA mice and the protective effect of dietary supplement agents. The results indicate that exposure to proton and HZE particle radiation significantly decreased the plasma level of total antioxidants in the irradiated CBA mice. Dietary supplementation with l-selenomethionine (SeM) or a combination of selected antioxidant agents (which included SeM) could partially or completely prevent the decrease in the total antioxidant status in the plasma of animals exposed to proton or HZE particle radiation. These findings suggest that exposure to space radiation may compromise the capacity of the host antioxidant defense system; this adverse biological effect can be prevented at least partially by dietary supplementation with agents expected to have effects on antioxidant activities.     

Emphasis of biological research for space radiation]

The paper summarized issues, current status and the recent topics in biological research of space radiation. Researches to estimate a risk associated with space radiation exposure during a long-term manned space flight, such as in the International Space Station, is emphasized because of the large uncertainty of biological effects and a complexity of the radiation environment in space. The Issues addressed are; 1) biological effects and end points in low dose radiation, 2) biological effects under low dose rate and long-term radiation exposure, 3) modification of biological responses to radiation under space environments, 4) various aspects of biological end points vs. cellular and molecular mechanisms, 5) estimation of human risk associated with radiation exposure in space flight, 6) regulations for radiation exposure limits for space workers. The paper also summarized and introduced recent progress in space related radiation researches with various biological systems.     

GSM 900 MHz microwave radiation affects embryo development of Japanese quails

A wide range of non thermal biological effects of microwave radiation (MW) was revealed during the last decades. A number of reports showed evident hazardous effects of MW on embryo development in chicken. In this study, we aimed at elucidating the effects of MW emitted by a commercial model of GSM 900 MHz cell phone on embryo development in quails (Coturnix coturnix japonica) during both short and prolonged exposure. For that, fresh fertilized eggs were irradiated during the first 38 h or 14 days of incubation by a cell phone in "connecting" mode activated continuously through a computer system. Maximum intensity of incident radiation on the egg's surface was 0.2 μW/cm2.The irradiation led to a significant (p<0.001) increase in numbers of differentiated somites in 38-hour exposed embryos and to a significant (p<0.05) increase in total survival of embryos from exposed eggs after 14 days exposure. We hypothesized that observed facilitating effect was due to enhancement of metabolism in exposed embryos provoked via peroxidation mechanisms. Indeed, a level of thiobarbituric acid (TBA) reactive substances was significantly (p<0.05-0.001) higher in brains and livers of hatchlings from exposed embryos. Thus, observed effects of radiation from commercial GSM 900 MHz cell phone on developing quail embryos signify a possibility for non-thermal impact of MW on embryogenesis. We suggest that the facilitating effect of low doses of irradiation on embryo development can be explained by a hormesis effect induced by reactive oxygen species (ROS). Future studies need to be done to clarify this assumption.     

Exposure to ultraviolet radiation (290-400 nm) causes oxidative stress, DNA damage, and expression of p53/p73 in laboratory experiments on embryos of the spotted salamander, Ambystoma maculatum

Developing embryos of the spotted salamander, Ambystoma maculatum, exposed to ultraviolet radiation (UVR; 290-400 nm) in the laboratory show a significant sensitivity to UVB (290-320 nm) radiation. Embryos in laboratory experiments exhibited significant DNA damage during exposures to UVR despite a significant increase in the production of the protective pigment melanin in response to UVR exposure. DNA damage occurs as a result of both the direct effects of exposure to UVR, and the indirect effects are mediated by the production of reduced oxygen intermediates. The production of reactive oxygen species initiates the expression of p53/p73 that leads to either DNA repair or apoptosis. When similar experiments are conducted on salamander embryos exposed to solar UVR in vernal pools, the embryos show significantly less sensitivity and higher survivorship. The differences between laboratory and field experiments are a result of the attenuation of UVR caused by the accumulation of dissolved organic carbon within the pools of these wooded areas. These findings suggest that northeastern populations of spotted salamanders are sensitive to UVR but are not significantly affected by present-day irradiances of UVR in the field. These results do suggest that continued decreases in stratospheric ozone over temperate latitudes have the potential to affect spotted salamanders in their natural habitats.     

Enhanced stress resistance of dormant bdelloids (rotifera)

Dormant rotifers (Macrotrachela quadricornifera) were exposed to several stresses on ground, on stratospheric balloons and on Shuttle, and their resistance was recorded iii terms of survival. On ground, active and dormant animals were exposed to temperature and gravity variations and to UV radiation. In all tests the dormant rotifers were significantly more resistant than the hydrated ones. On balloons, dormant animals were exposed during approx. 20-h-flight to stratospheric conditions such as vacuum broad temperature changes and radiation. Recovery was rather poor, but the result could not be ascribed to any particular factor, because effect of single factors could not be discriminated. On Shuttle, dormant rotifers were exposed to hypogravity and vibrations and their recovery was very similar to ground controls. On the whole, dormant animals were more resistant than active ones under lab conditions, but no experiment has been run exposing active and dormant rotifers to space conditions, so far.     

Ultraviolet light‐induced impairment of goldfish embryo development and evidence for photorepair mechanisms

Goldfish Carassius auratus embryos were subjected to artificial ultraviolet‐B (UVB) radiation (280–320 nm) at various times during development to evaluate the effects on production of anatomically normal larvae. The UVB radiation used in these experiments included a higher proportion of shorter wavelengths compared to the natural spectrum. The development of embryos exposed to UVB for 2 or 4 h at 26 h post‐fertilization was severely impaired whereas similar exposures at 50 or 74 h post‐fertilization had no effect. A 2 h exposure to UVB commencing at 2 h post‐fertilization did not adversely affect embryonic development whereas a 4 h exposure to a lower dose did. At 50 h post‐fertilization, when embryos were normally resistant to UVB, denial of access to visible light and UVA before, during and after exposure to UVB caused impairment of development. Analysis of DNA fragment length after incubation with an endonuclease suggested that UVB damage at 50 h was caused by formation of pyrimidine dimers. This study demonstrated that the sensitivity of goldfish embryos to UVB varied during development and that resistance to UVB in later developmental stages included a photorepair mechanism.     

Effects of dietary supplements on space radiation-induced oxidative stress in Sprague-Dawley rats

Of particular concern for the health of astronauts during space travel is radiation from protons and high-mass, high-atomic-number (Z), and high-energy particles (HZE particles). Space radiation is known to induce oxidative stress in astronauts after extended space flight. In the present study, the total antioxidant status was used as a biomarker to evaluate oxidative stress induced by gamma rays, protons and HZE-particle radiation. The results demonstrate that the plasma level of total antioxidants in Sprague-Dawley rats was significantly decreased (P < 0.01) in a dose-dependent manner within 4 h after exposure to gamma rays. Exposure to protons and HZE-particle radiation also significantly decreased the serum or plasma level of total antioxidants in the irradiated animals. Diet supplementation with L-selenomethionine alone or a combination of selected antioxidant agents was shown to partially or completely prevent the decrease in the serum or plasma levels of total antioxidants in animals exposed to gamma rays, protons or HZE particles. These findings suggest that exposure to space radiation may compromise the capacity of the host antioxidant defense and that this adverse biological effect can be prevented at least partially by dietary supplementation with L-selenomethionine and antioxidants.     

Effects of dietary antioxidant supplementation on the development of malignant lymphoma and other neoplastic lesions in mice exposed to proton or iron-ion radiation

Malignancy is considered to be a particular risk associated with exposure to the types of ionizing radiation encountered during extended space flight. In the present study, two dietary preparations were evaluated for their ability to prevent carcinogenesis in CBA mice exposed to different forms of space radiation: protons and highly energetic heavy particles (HZE particles). One preparation contained a mixture of antioxidant agents. The other contained the soybean-derived Bowman-Birk protease inhibitor (BBI), used in the form of BBI Concentrate (BBIC). The major finding was that there was a reduced risk of developing malignant lymphoma in animals exposed to space radiation and maintained on diets containing the antioxidant formulation or BBIC compared to the irradiated animals maintained on the control diet. In addition, the two different dietary countermeasures also reduced the yields of a variety of different rare tumor types observed in the animals exposed to space radiation. These results suggest that dietary supplements could be useful in the prevention of malignancies and other neoplastic lesions developing from exposure to space radiation.     

The effects of UV radiation on photosynthesis in an Antarctic diatom (Thalassiosira sp.): Does vertical mixing matter?

The reduction of Antarctic stratospheric ozone results in significant increases in ultraviolet B radiation (UVB-R, 280-320 nm) reaching ocean's surface, potentially damaging phytoplankton. Several studies refer to the negative direct and indirect effects of UVB-R and ultraviolet A (UVA-R, 320-400 nm, which is not modified by ozone concentration) on different targets within algal cells. There are, however, internal and external processes, like vertical mixing, which can in part counteract such effects. The hypothesis that vertical mixing is a significant factor reducing the negative effects of ultraviolet radiation (UV-R, 280-400 nm) on planktonic algae photosynthesis was tested at Potter Cove (South Shetland Is., Antarctica). Three laboratory (solar simulator, SOLSI) and two field (natural Sun exposure) experiments were conducted. Vertical mixing was studied exposing cells of Thalassiosira sp., a typically bloom forming diatom in Antarctic waters, to variable light conditions simulating 6 h cycles (Mix treatment), whereas incubations at two fixed depths were used as controls (0.5 and 5 m, S_fix and D_fix treatments, respectively). Light effects were studied for each of the previous exposure conditions considering three treatments: PAR-T (exposure to PAR, photosynthetic active radiation, 400-700 nm), UVA-T (exposure to PAR and UVA-R) and UVB-T (exposure to PAR, UVA-R and UVB-R). During SOLSI experiments no significant differences were found between the different light treatments under simulated normal and medium ozone concentrations. Under low ozone conditions, 40% reduction in photosynthesis was observed in the UVB-T for surface incubations. In contrast, no significant differences were observed among the light treatments under mixing conditions. Field and laboratory experiments showed similar results. However, during one of the field experiments when ozone was low, not only S_fix but Mix incubations presented a significant reduction in photosynthesis, suggesting that vertical mixing under such conditions was not efficient enough to prevent harmful UVB-R effects. On the other hand, during a day with high insulation and normal ozone, but with elevated absorption of light in the water column, no significant effects of any of the studied factors were detected.In conclusion, vertical mixing was shown to play a significant role in protecting algae under low ozone concentrations, lessening photoinhibition by UVB radiation. The differences between laboratory and field experiments are discussed in terms of the relative significance of UVB-R dose and dose rate on both types of experiments.     

Effects of temperature and UV radiation increases on the photosynthetic efficiency in four scleractinian coral species

Experiments were performed on coral species containing clade A (Stylophora pistillata, Montipora aequituberculata) or clade C (Acropora sp., Pavona cactus) zooxanthellae. The photosynthetic efficiency (F(v)/F(m)) of the corals was first assessed during a short-term increase in temperature (from 27 degrees C to 29 degrees C, 32 degrees C, and 34 degrees C) and acute exposure to UV radiation (20.5 W m(-2) UVA and 1.2 W m(-2) UVB) alone or in combination. Increasing temperature to 34 degrees C significantly decreased the F(v)/F(m) in S. pistillata and M. aequituberculata. Increased UV radiation alone significantly decreased the F(v)/F(m) of all coral species, even at 27 degrees C. There was a combined effect of temperature and UV radiation, which reduced F(v)/F(m) in all corals by 25% to 40%. During a long-term exposure to UV radiation (17 days) the F(v)/F(m) was significantly reduced after 3 days' exposure in all species, which did not recover their initial values, even after 17 days. By this time, all corals had synthesized mycosporine-like amino acids (MAAs). The concentration and diversity of MAAs differed among species, being higher for corals containing clade A zooxanthellae. Prolonged exposure to UV radiation at the nonstressful temperature of 27 degrees C conferred protection against independent, thermally induced photoinhibition in all four species.     

Genetic Variability of Flight Metabolism in DROSOPHILA MELANOGASTER . III. Effects of Gpdh Allozymes and Environmental Temperature on Power Output

The effect of allozyme variation at the sn-glycerol-3-phosphate dehydrogenase (Gpdh) locus on variation in the mechanical power output of the flight muscles of Drosophila melanogaster was investigated. The influence of different rearing and flight temperatures and of their interactions with the Gpdh allozymic genotypes (allotypes) on flight ability also were analyzed. Populations from three continents were used, and Gpdh allotypes were generated from crosses between randomly paired isofemale lines made autozygous for each of the two alleles by inbreeding. Measurements made during tethered flight, together with wing morphology, were used to estimate power output using both Weis-Fogh's and Ellington's formulas. Analyses of variance (ANOVA) indicated significant main effects for both environmental components (rearing and flight temperatures) but for only one of the three genetic components (genetic backgrounds within continent); Gpdh allotypes and populations (continent of origin) were not significant. The interaction between rearing and flight temperature was highly significant, indicating some physiological adaptation. The effect of Gpdh allozymes depended on both rearing and flight temperature and was either significant or marginally so, depending on which set of formulas was used. In either case, the S/S allotype showed a 2-4% greater power output than the F/F allotype at low temperature for both interactions. In addition, the S/S allotype showed significantly greater power output than the F/F allotype among flies raised at 15 degrees and flown at 15 degrees, whereas the reverse was true for flies raised at 30 degrees and flown at 30 degrees. Significant differences among the three allotypes for GPDH activity level were found in general, with S/S having the highest, F/S intermediate and F/F the lowest activity, and an inverse relationship existed between rearing temperature and activity. The temperature effects on power output are consistent with the geographical and seasonal variation observed at the Gpdh locus in nature. In general, the results show that Gpdh can be considered a minor polygene affecting quantitative variation in the power output during flight and that genotype-by-environment interaction is an important component of that effect.     

Amphibian defenses against ultraviolet-B radiation

As part of an overall decline in biodiversity, amphibian populations throughout the world are disappearing. There are a number of potential causes for these declines, including those related to environmental changes such as increasing ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion. UV-B radiation can kill amphibian embryos or can cause sublethal effects that can harm amphibians in later life stages. However, amphibians have defenses against UV-B damage that can limit damage or repair it after exposure to UV-B radiation. These include behavioral, physiological, and molecular defenses. These defenses differ interspecifically, with some species more able to cope with exposure to UV-B than others. Unfortunately, the defense mechanisms of many species may not be effective against increasing persistent levels of UV-B radiation that have only been present for the past several decades due to human-induced environmental damage. Moreover, we predict that persistent UV-B-induced mortality and sublethal damage in species without adequate defenses could lead to changes in community structure. In this article we review the effects of UV-B radiation on amphibians and the defenses they use to avoid solar radiation and make some predictions regarding community structure in light of interspecific differences in UV-B tolerance.     

The embryonic development of Xenopus laevis under a low frequency electric field

The aim of this study was to determine the effects of a low frequency electric field on the early embryonic development of frogs. The embryos of African clawed toads, Xenopus laevis, were exposed to a 20-μA electric current during the cleavage stages. The developmental processes of embryos during and after electric field exposure were monitored for teratogenic effects. All the embryos continuously exposed to the electric field died without undergoing any developmental processes. However, when the embryos were exposed to the electric field for 20-min periods (four times/over 2 d), the embryos developed into both normal tadpoles (70 %) and malformed tadpoles with light edema, reduced pigmentation, or axial anomalies, such as crooked tails. After exposure, the control embryos were at development stage 35.5 (2 d 2 h), while the normal embryos of the assay group were at developmental stage 41(3 d 4 h). There was a 1 d 2 h difference between the two developmental stages, revealing the importance of that time period for embryogenesis. In conclusion, the effects of electric current on Xenopus embryos are dependent on the initial developmental stage and the duration of exposure.     

Effect of temperature on secondary metabolites production and antioxidant enzyme activities in Eleutherococcus senticosus somatic embryos

Somatic embryos of Eleutherococcus senticosus were exposed at 12, 16, 24 and 30 °C for duration of 45 days in bioreactor. The effects of such treatments on the growth, eleutheroside B, E, E₁, total phenolics, flavonoids, chlorogenic acid concentrations and antioxidant enzymes activities were investigated. The results revealed that low (12 and 18 °C) and high (30 °C) temperature caused significant decrease in fresh weight (FW), dry weight (DW), total phenolics, flavonoids and total eleutheroside accumulation, while low temperature increased eleutheroside E accumulation in somatic embryos. Low temperature significantly increased superoxide dismutase (SOD), catalase (CAT), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) activities whereas a strong increase in ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) activity was obtained at 12 °C grown somatic embryos. In contrast, high temperature significantly decreased antioxidant enzymes activities and even guaiacol peroxidase (G-POD) activity also decreased at low temperature in comparison to 24 °C grown embryos. These data suggest that low and high temperature treatment provoked an oxidative stress in E. senticosus embryos, as shown by the increase in lipid peroxidation. The increase in lipid peroxidation was paralleled by a rise in lipoxygenase (LOX) activity and hydrogen peroxide (H₂O₂) content. However, this stress was more prominent at high temperature than low temperature grown embryos. This result suggests that the reduced growth of embryo at 30 °C was concomitant with reduced efficiency of these protective enzymes. On the other hand, increases in antioxidant activities at 12 and 18 °C could also be a response to the cellular damage; however, this increase could not stop the deleterious effects of low temperature, but reduced stress severity thus allowing embryo growth to occur.     

Physiological and biochemical responses of fruit exocarp of tomato (Lycopersicon esculentum Mill.) mutants to natural photo-oxidative conditions

Photo-oxidative stress was imposed under natural solar radiation on exposed and shaded sections of detached fruit of immature green tomato (Lycopersicon esculentum Miller = Solanum lycopersicum L.) mutants (anthocyanin absent, beta-carotene, Delta, and high pigment-1) and their nearly isogenic parents ('Ailsa Craig' and 'Rutgers'). After 5 h exposure to high solar irradiance, either with or without ultraviolet (UV) radiation, surface colour changes, pigment composition, photosynthetic efficiency, antioxidant metabolites and enzyme activities, and selected flavonoids and antioxidant proteins in exocarp tissue were evaluated. The imposed photo-oxidative stress reproduced the symptoms observed on attached fruit. Both high temperature and solar irradiance caused fruit surface discoloration with faster degradation of chlorophyll (Chl) than carotenoids (Car), leading to an increase in the Car/Chl ratio. Surface bleaching was mostly caused by visible light, whereas elevated temperatures were mostly responsible for the inactivation of photosynthesis, measured as decreased F(v)/F(m). Ascorbate, glutathione, and total soluble protein concentrations decreased in the exocarp as the duration of exposure increased. Specific activities of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), and catalase increased with exposure, suggesting that these proteins were conserved during the imposed stress. GR protein expression remained stable during the imposed stress, whereas, MDHAR protein expression increased. Quercetin and kaempferol concentrations increased rapidly upon exposure, but not to UV radiation, suggesting rapid photo-protection in response to visible light; however, naringenin synthesis was not induced. The apparent increased tolerance of hp-1 fruit is discussed.     

低温20℃对意大利蜜蜂未受精卵发育的影响

【目的】蜜蜂是狭温性昆虫的代表,低温对意大利蜜蜂Apis mellifera ligustica未受精卵发育的影响尚不清楚。【方法】将0~66 h卵龄的意大利蜜蜂未受精卵放置在20℃下分别处理梯度时间。【结果】低温20℃导致意大利蜜蜂未受精卵的孵化率下降,发育历期延长。0、3、6、9 h卵龄的卵对低温极敏感,处理0.5 h孵化率下降,处理4.0 h,全部死亡;发育12、24 h的卵在低温中处理4.0 h不受影响(P>0.05),处理12.0 h,全部死亡;发育36 h以上的卵则较耐低温,处理12.0 h无影响(P>0.05),处理36.0 h,各卵龄没有全部死亡,其中最低的孵化率为25.4%。12~66 h的卵在低温20℃下的发育历期(y)与处理时间(x)呈现显著的线性回归关系,发育历期延长的时间约等于处理时间长。【结论】意大利蜜蜂未受精卵对低温20℃的敏感性与卵龄关系密切,低卵龄的意大利蜜蜂未受精卵比高卵龄更易受低温影响。这些结果为深入研究温度对蜜蜂胚胎发育影响的机制奠定基础,也为蜜蜂的科学饲养提供了理论依据。     

Reviewing the Technical Designs for Experiments with Ultraviolet-B Radiation and Impact on Photosynthesis, DNA and Secondary Metabolism

The ultraviolet-B (UV-B) portion of sunlight has received much attention in the last three decades, because radiation from this spectral region increases due to the stratospheric ozone depletion, which results from increases of chlorofluorocarbons in the atmosphere. Plant responses to UV-B exposure vary greatly and the interpretation of and comparison between studies is hindered, mainly by the contrasting experimental conditions used and interactive factors such as low light levels and possible artifacts due to the artificial experimental conditions. It seems likely that increases in solar UV-B radiation of the magnitude anticipated under current stratospheric ozone projections will not significantly inhibit photosynthesis and cause DNA damage in plants. This is in part due to the well-evolved protection mechanisms present in most plant species. One of the significant plant responses to UV-B is changes in foliar secondary chemistry, which could be translated into significant effects at higher trophic levels through plant-herbivore interactions and decomposition. Enhanced UV-B radiation due to stratospheric ozone depletion could also cause morphological changes that would affect competitive interactions, especially if contrasting UV-B sensitivity exists among the competitors.     

Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms isolated from the Solthörn tidal flat (Lower Saxony,southern North Sea) – Part I: growth and antioxidative defence strategies

The unconsolidated sediment of intertidal mudflats constitutes a highly unstable environment, due to continuously changing water levels and currents as well as temporary exposure to the air. Therefore, diatoms inhabiting marine intertidal areas are subjected to strongly changing surface light and UV intensities due to exposure at low tide. Five marine intertidal diatoms (Achnanthes exigua, Cocconeis peltoides, Diploneis littoralis, Navicula digitoradiata and Amphora exigua) were isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea). Semi-continuous cultures were used to determine the effect of UV radiation (photosynthetically active radiation only [PAR], PAR+UV-B, PAR+UV-A, PAR+UV-B+UV-A) during short- and long-term exposure (6 h or 30 days). Growth rates, chlorophyll a (chl a), antioxidant capacities, accumulation of phenolic compounds (e.g. flavonoids) and DMSP, and activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase and glutathione reductase) were assessed. UV-A had only minor effects on cells, while growth rate, chl a content and protein content were significantly reduced after long-term UV-B exposure. Achnanthes exigua extracts showed the highest antioxidant capacity. The highest activity of SOD, APX and MDHAR was found under long-term combined UV exposure (PAR+UV-B+UV-A). Overall, the antioxidative defence of the five isolates was stimulated during exposure to UV radiation, as may be found during emersion. Emersion induces oxidative stress and, as a result, growth of the five diatom taxa was inhibited to suit changing environmental conditions. All five taxa tested in the present study showed species-specific acclimatization potentials, providing possible explanations for variability in population, species composition and ecosystem structures in the face of climatic variations.