UV-B induced changes in antioxidant enzymes and their isoforms in cucumber (Cucumis sativus L.) cotyledons

To assess the role of antioxidant defense system on exposure to ultra-violet-B (UV-B) radiation, the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of antioxidants ascorbic acid (AA) and alpha-tocopherol were monitored in cucumber (Cucumis sativus L. var long green) cotyledons. UV-B enhanced the activity of antioxidant enzymes as well as AA content, but decreased the level of alpha-tocopherol. Significant increase was observed in the activities of SOD and GPX. Analysis of isoforms of antioxidant enzymes by native-PAGE and activity staining revealed three isoforms of GPX in unexposed dark-grown cotyledons (control), and their intensity was enhanced by UV-B exposure. In addition, four new isoforms of GPX were observed in cotyledons after UV-B exposure. Although no new isoforms were observed for the other antioxidant enzymes, the activities of their existing isoforms were enhanced by UV-B.     

Responses of the flavonoid pathway to UV-B radiation stress and the correlation with the lipid antioxidant characteristics in the desert plant Caryopteris mongolica

Caryopteris mongolica is a dwarf shrub mainly found in grassland and desert areas of north-west China, and which can survive severe environmental stress. This study aimed to assess the responses of the flavonoid pathway to UV-B radiation treatments and its correlation to the lipid peroxide and antioxidant systems in C. mongolica. In UV-B radiation experiments, plants were exposed to UV-B radiation treatments with a intensity of 30 J/s for 1, 4 and 24 h, respectively. A control group without UV-B radiation treatment was also used. The chlorophyll fluorescence parameters, contents of chlorophyll and carotenoid, levels of lipid peroxidation, activities of antioxidant system enzymes, accumulations of total flavonoids and anthocyanins, and activities of phenylalanine ammonialyase (PAL) and chalcone isomerase (CHI) under different UV-B radiation treatments were investigated. The correlations between products and key enzymes in the flavonoid pathway and the lipid peroxide and antioxidant systems were also analyzed. The results showed that chlorophyll fluorescence parameters decreased within 24 h of treatment. The chlorophyll contents decreased within 4 h and remained stable after 24 h. Carotenoid content significantly increased. The level of MDA, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and peroxidase (POD) and the contents of total flavonoids and anthocyanidins increased, while catalase (CAT) activity decreased under UV-B stress. The activities of PAL and CHI also increased with the increased content of total flavonoids. The flavonoid products anthocyanidins had a significant positive correlation with MDA level, as well as the activities of antioxidant enzyme SOD. In conclusion, UV-B radiation induced the degradation of photosynthetic pigments and decreased photochemical efficiency of Photosystem II; increased the contents of MDA, total flavonoids and anthocyanidins; and also enhanced activities of antioxidant enzymes (SOD, APX and POD) and key enzymes (PAL and CHI) in the flavonoid pathway in C. mongolica. Thus, we speculate that the flavonoid pathway were involved in the regulation of stress resistance in C. mongolica.     

干旱胁迫对2种光合类型C4荒漠植物叶片光合特征酶和抗氧化酶活性的影响

以荒漠C₄草本植物蔷薇猪毛菜(NADP苹果酸酶型,NADP-ME）和粗枝猪毛菜（NAD苹果酸酶型,NAD-ME）为研究对象,采用盆栽控水试验设置正常供水和轻度、中度、重度干旱处理（土壤含水量分别为田间持水量80%、60%、45%和35%）,通过测定不同程度干旱胁迫下叶片含水量、C₄光合特征酶和抗氧化酶活性等指标,探讨不同类型C₄荒漠植物光合特征酶和抗氧化系统对干旱逆境的适应机制。结果显示：（1）2种植物叶片含水量均随干旱胁迫的加剧不同程度降低。（2）叶片磷酸烯醇式丙酮酸羧化酶（PEPC）活性在中度干旱胁迫下显著增加而在重度干旱胁迫下急剧下降;蔷薇猪毛菜NAD-ME活性和粗枝猪毛菜NADP-ME活性都很低,且它们基本不受干旱胁迫的影响;随干旱胁迫的加剧,蔷薇猪毛菜NADP-ME活性呈下降趋势,而粗枝猪毛菜NAD-ME活性先显著增加而在重度干旱胁迫下显著降低。（3）随着干旱胁迫的加剧,叶片超氧化物歧化酶（SOD）活性呈下降趋势,过氧化物酶（POD）活性在不同程度干旱胁迫下均有不同程度增加;过氧化氢酶（CAT）活性在中度干旱胁迫下均有不同程度的增加,但在重度干旱胁迫下蔷薇猪毛菜CAT活性降低,而粗枝猪毛菜CAT活性显著增加;丙二醛（MDA）含量随干旱胁迫的加剧均有不同程度的增加。研究认为,一定程度干旱胁迫下,2种荒漠植物的PEPC活性均有增加;不同光合类型C₄植物叶片脱羧酶（NADP-ME和NAD-ME）对干旱胁迫的响应有明显的差异。POD和CAT是这两种C₄植物适应干旱胁迫的主要抗氧化酶,但蔷薇猪毛菜CAT在重度干旱胁迫下没有起到积极保护作用。     

<Emphasis Type="Italic">Isatis indigotica</Emphasis> seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B

Sterilized seeds of Isatis indigotica (Brassicacae) were divided into four groups based on irradiation pretreatments. These control groups (C) were non irradiated, He–Ne laser treated seeds (L), UV-B treated seeds (B) and He–Ne laser followed by UV-B radiation treated seeds (LB). Laser radiation was provided by He–Ne laser, UV-B radiation was provided by filtered Qin brand 30 W fluorescent sun lamps. Malondialdehyde (MDA), proline, UV-B absorbing compounds and ascorbic acid (AsA) concentrations, as well as, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were measured in the cotyledons of seedlings from all the four irradiation treatments. The result indicate that UV-B radiation enhanced the concentration of MDA while decreasing the activities of SOD, CAT, POD and the concentration of AsA in the seedlings compared with the controls. The concentration of MDA decreased, while the activities of SOD, CAT, POD and the concentration of AsA increased in seedling treated with He–Ne laser and UV-B compared to UV-B alone. The concentration of proline and UV absorbing compounds increased progressively with treatments i.e. UV-B irradiation, He–Ne laser irradiation, and He–Ne laser irradiation followed by UV-B irradiation compared to the controls. The present data suggest that Isatis indigotica seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B.     

He-Ne激光对增强UV-B辐射下小麦幼苗膜脂过氧化的缓解作用

采用He-Ne激光(5 mW/mm2)辐照增强UV-B辐射(10.08 kJ/m2.d)的晋麦8号小麦幼苗,通过测定小麦幼苗叶片细胞质膜透性、丙二醛(MDA)的含量以及脂氧合酶(LOX)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)和谷光苷肽过氧化物酶(GPX)的活性变化,研究He-Ne激光对增强UV-B辐射的小麦幼苗膜脂过氧化的影响。结果显示,He-Ne激光辐照可使经UV-B辐射后小麦幼苗叶片质膜相对透性、MDA含量、LOX活性降低,而使CAT、APX和GPX的活性均升高。分析表明UV-B辐射增强可导致膜脂过氧化加剧,而一定剂量的He-Ne激光能够通过促进酶促抗氧化系统酶的活性来缓解紫外线辐射下小麦幼苗的膜脂过氧化作用。     

Role of salicylic acid in regulating ultraviolet radiation-induced oxidative stress in pepper leaves

The effect of salicylic acid (SA) counteracting the UV-A, UV-B, and UV-C-induced action on pepper (Capsicum annuum L.) plants was studied. For this purpose, the activities of antioxidant enzymes (peroxidase, polyphenol oxidase, ascorbate peroxidase, catalase, and glutathione reductase) were measured. Plants were sprayed with SA and treated with UV-A (320–390 nm), UV-B (312 nm), and UV-C (254 nm) radiation with a density of 6.1, 5.8, and 5.7 W/m². The activities of antioxidant enzymes were enhanced in leaves in response to UV-B and UV-C radiation. SA treatment moderated an increase in the activities of some antioxidant enzymes (peroxidase, ascorbate peroxidase, catalase, and glutathione reductase) in plants that were treated with UV radiation. The activity of antioxidant enzyme polyphenol oxidase in plants that were treated with UV-B, UV-C, and SA was significantly increased. The aim of the present study was to investigate the possible protective effect of SA treatment on UV-A, UV-B, and UV-C stress.     

Modulation of enzyme activities and expression of genes related to primary and secondary metabolism in response to UV-B stress in cucumber (Cucumis sativus L.)

Abstract

Exposure to UV-B at ambient or enhanced levels is known to trigger a variety of responses in all living organisms, including higher plants. Here we show that in Cucumis sativus L. UV-B radiation affects enzyme activity of key oxydative pentose phosphate pathway (OPPP) enzymes glucose-6-phosphate dehydrogenase (G6P-DH) and 6-phosphogluconate dehydrogenase (6-PGlu-DH), of key phenolic compounds enzyme phenylalanine ammonia lyase (PAL) as well as erythrose-4-phosphate, tryptophan and tyrosine levels. Furthermore, we found an increased activity of antioxidant enzymes such as peroxidase (POX) and catalase (CAT) in treated plants, with respect to the controls. In order to confirm the biochemical results, we isolated total RNA from both controls and UV-B treated plants to be used for gene expression analysis. We demonstrated that UV-B increases the gene expression level of peroxidase (POX), catalase (CAT) and phenylalanine ammonia lyase (PAL). Finally, our results are useful for understanding protective strategies against UV-B radiation and for elucidating what components are involved in stress-induced signals within the plant.     

Localization of antioxidant enzymes in the cellular compartments of sorghum leaves

The localization of antioxidant enzymes between the mesophyll and bundle sheath cells were determined in sorghum (Sorghum vulgare L.) leaves. The activity of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) were assayed in whole leaf, mesophyll and bundle sheath fractions of sorghum leaves subjected to water-limited conditions. Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5–2.0 MPa. The purity of the isolates was tested using the marker enzymes like RuBPcase and PEPcase. GR was mostly localized in mesophyll fraction, while SOD, APX and peroxidase were located in bundle sheath cells. Catalase was found to be equally distributed between the two cell types. Under water stress conditions, most of the SOD activity was found in the bundle sheath tissues. Little or no activity of the enzymes CAT, APX or POD was found in the mesophyll extracts when exposed to water stress. GR activity increased when exposed to low water regimes. From this study, it is clear that antioxidants are differentially distributed between the mesophyll and bundle sheath cells in sorghum leaves. Under water stress conditions, the mesophyll cells showed less damage from oxidative stress when compared to the bundle sheath cells. This is critical for determining the sensitivity of sorghum to extreme climatic conditions.     

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.     

Enhancement of antioxidant production in <Emphasis Type="Italic">Spirulina platensis</Emphasis> under oxidative stress

The present study examined the possibility of increasing the contents of some bioactive compounds of Spirulina platensis cultivated in medium containing various hydrogen peroxide concentrations (2, 4, 6 and 8 mM) as a model for environmental stress. A positive correlation was observed between the increase of H₂O₂ and increasing amounts of cellular lipophilic antioxidants (total carotenoids and α-tocopherol) and hydrophilic antioxidants [glutathione (GSH) and ascorbic acid (AsA)]. HPLC profile of carotenoids revealed that algae responded to the change of H₂O₂ exposure by the accumulation of higher amounts of β-carotene, astaxanthine, luteine, zeaxanthin and cryptoxanthin. S. platensis showed significant linear increase in activities of antioxidant enzymes, i.e., catalase (CAT), peroxidase (PX), ascorbate peroxidase (APX) and superoxide dismutase (SOD), with increasing H₂O₂ concentrations. A pronounced increase of oxidative lesions’ indexes [thiobarbituric acid reactive substances (TBARS) and paramagnetic radical-EPR signal] was found in algal grown at 8 mM H₂O₂. These data revealed that S. platensis behaved with different strategies against H₂O₂ exposure which is dose dependent and their response strongly correlated with the scavenging enzymes (SOD, CAT, PX and APX) and antioxidant compounds (GSH, AsA, β-carotene, astaxanthine and α-tocopherol) in the antioxidant defense systems. Therefore, S. platensis could be considered as good candidates for successful cultivation in artificial open ponds under different environmental conditions, as high value health foods, functional foods and as source of wide spectrum of nutrients.     

Antioxidant defense system in leaves of Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassica juncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.     

Changes in activities of antioxidant enzymes and their gene expression during leaf development of sweetpotato

To understand the functions of antioxidant enzymes during leaf development in sweetpotato, we investigated the activities of several antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APX) and catalase (CAT). Significant increases were observed in the activities of SOD, POX and APX during the late stage of leaf development, whereas CAT activity increased during the early developmental stage. By RT-PCR analysis, various POX and APX genes showed differential expression patterns during leaf development. Four POX genes swpa3, swpa4, swpa6, swpb4 and one APX gene swAPX1 exhibited high levels of gene expression during the senescence stage of leaf development, but two POX genes, swpa1 and swpa7 were preferentially expressed at both the mature green and the late senescence stages of leaf development. These results indicate that hydrogen peroxide (H₂O₂)-related antioxidant enzymes are differentially regulated in the process of leaf development of sweetpotato.     

Cloning, expression and physiological analysis of broccoli catalase gene and Chinese cabbage ascorbate peroxidase gene under heat stress

The objectives of this work were to clone the catalase (CAT) gene from broccoli (Brassica oleracea) and the ascorbate peroxidase (APX) gene from Chinese cabbage and measure the regulation of CAT and APX gene expressions under heat-stress conditions. Different genotypes responded differently to heat stress according to their various antioxidant enzymes and physiological parameters. CAT and APX gene expression profiles were well matched with the data for CAT and APX enzyme activities in the broccoli and Chinese cabbage plants, respectively. Full-length of the CAT and APX cDNA were 1,768 and 1,070 bp, respectively. A phylogenetic analysis of CAT and APX indicated that plant CATs and APXs diverged into two major clusters.     

Antioxidant enzymes as biochemical markers for sharka resistance in apricot

The activity of antioxidant enzymes in different apricot (Prunus armeniaca L.) cultivars, resistant or susceptible to Plum pox virus (PPV), was analyzed during the years 2002 and 2003. Resistant cultivars showed higher activities of catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) than susceptible cultivars. Only CuZn-SOD isozymes were detected in the apricot cultivars. However, no correlation was observed between this isozyme pattern and the resistance to PPV. On the other hand, PPV-resistant apricot cultivars could have a greater capability for elimination of H₂O₂ and recycling of ascorbate-glutathione cycle, and they have at least two of these enzymatic activities (CAT, APX and DHAR) over the average. In contrast, this response was not observed in the susceptible cultivars. All these data suggest that the activities of CAT, APX and DHAR could be used as biochemical markers of sharka resistance in apricot.     

Effects of Chromium Picolinate on Oxidative Damage in Primary Piglet Hepatocytes

A proven photocatalyst, titanium dioxide in the form of nano-anatase, is capable of undergoing electron transfer reactions under light. In previous studies, we had proven that nano-anatase could absorb ultraviolet light (UV-B) and convert light energy to stable chemistry energy finally via electron transport in spinach chloroplasts.The mechanisms by which nano-anatase promotes antioxidant stress in spinach chloroplasts under UV-B radiation are still not clearly understood. In the present paper, we investigate the effects of nano-anatase on the antioxidant stress in spinach chloroplasts under UV-B radiation. The results showed that nano-anatase treatment could significantly decrease accumulation of superoxide radicals, hydrogen peoxide (H₂O₂), and malonyldialdehyde (MDA) content, and increase activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and elevate evolution oxygen rate in spinach chloroplasts under UV-B radiation. Together, nano-anatase could decrease the oxidative stress to spinach chloroplast caused by UV-B radiation.     

Cadmium mitigates ultraviolet-B stress in Anabaena doliolum: Enzymatic and non-enzymatic antioxidants

Impact of ultraviolet-B (UV-B) and Cd, applied individually and in combination, measured in terms of oxygen-evolution, chlorophyll (Chl) and protein contents, lipid peroxidation, and enzymatic and non-enzymatic antioxidants of Anabaena doliolum, revealed a greater oxidative damage induced by UV-B than by Cd. While superoxide dismutase (SOD) showed a greater stimulation by UV-B than Cd, the activities of catalase (CAT) and glutathione reductase (GR) declined after UV-B treatment. Cd treatment, however, enhanced the activities of ascorbate peroxidase (APX) and GR. CAT activity increased at low but decreased at high dose of Cd. Increase in carotenoid (Car) content in UV-B treated cells suggested a shielding effect of Car against UV-B stress. A 15-and 10-fold rise in α-tocopherol (α-TOC) content at high dose of Cd and/or UV-B offered testimony to the antioxidant role of α-TOC.     

Protective role of selenium in wheat seedlings subjected to enhanced UV-B radiation

Selenium (Se) is beneficial for some plants and is able to increase resistance and antioxidant capacity of plants subjected to stressful environment. In this work, the effects of enhanced ultraviolet-B (UV-B) radiation, Se supply, and their combination on growth and physiological traits of wheat (Triticum aestivum L., cv. Han NO.7086) seedlings were studied. The objective was to elucidate whether Se could alleviate the expected adverse effects of UV-B stress on seedlings. UV-B treatment caused a marked decline in growth parameters and total chlorophyll content and changed biomass allocation between aboveground and underground parts, which led to an increase in the root/shoot ratio. UV-B treatment also increased MDA content and the rate of superoxide radical (O₂^·−) production, although it increased some antioxidant (proline, phenolic compounds, and flavonoids) content and activity of antioxidant enzymes (peroxidase, superoxide dimutase, catalase (CAT)). Se treatment only increased total chlorophyll content and CAT activity. Compared with UV-B treatment alone, the combined treatment with UV-B and Se induced a significant increase in the biomass, total chlorophyll content, antioxidant content, and activity of antioxidant enzymes, and an evident decrease in MDA content and the rate of O₂^·− production. The results of this study demonstrated that Se alleviated the damage caused by UV-B to wheat seedlings to some extent by increasing antioxidant enzyme activity and antioxidant content.     

Effects of paraquat on lipid peroxidation and antioxidant enzymes in aquatic fern <Emphasis Type="Italic">Azolla microphylla</Emphasis>

Paraquat is most extensively used methyl viologen herbicide to control weeds in the rice-Azolla ecosystem. The effects of different paraquat (PQ) dosages on growth, lipid peroxidation, and activity of antioxidant enzymes of Azolla microphylla Kaul. were investigated. The results indicated that Azolla fronds survived only at the concentrations of 2–6 μM PQ. Frond fragmentation and browning occurred after 24 h at 8 μM PQ. At 24 h, the amount of proteins decreased by 48.7 % in Azolla fronds exposed to 10 μM PQ than that in control fronds. The supplementation of 10 μM PQ increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) by 2,4-, 1,8-, 3,0-, and 2,2-fold, respectively, as compared with control. The content of PQ and activities of SOD, CAT, GPX, and APX were found to be positively correlated. Our study showed that PQ (2–6 μM) caused ROS overproduction in Azolla fronds, which were scavenged by induced activities of antioxidant enzymes.     

Effect of UV-B radiation on the growth and antioxidant enzymes of Antarctic sea ice microalgae <Emphasis Type="Italic">Chlamydomonas</Emphasis> sp. ICE-L

The effect of ultraviolet-B (UV-B) radiation on Antarctic phytoplankton has become an attractive ecological issue as a result of annual springtime ozone depletion. The effects of UV-B radiation on the growth and antioxidant enzymes were investigated using Antarctic sea ice microalgae Chlamydomonas sp. ICE-L as the material in this study. The results demonstrated that UV-B radiation could notably inhibit the growth, especially at high UV-B radiation intensity (70 μW cm⁻²). Malondialdehyde and O₂ ^·− content in ICE-L increased rapidly in early days (1–3 days) exposed to UV-B radiation enhancement, then decreased rapidly. In the stress of UV-B radiation enhancement, the superoxide dismutase, peroxidase and Catalase activities of 1–4 days in ICE-L were obviously higher than those in the control, and their activities became higher at high UV-B radiation intensity (70 μW cm⁻²). These enzymes activity of 7 days would kept stable at low UV-B radiation intensity (35 μW cm⁻²), but kept high level at high UV-B radiation intensity (70 μW cm⁻²). However, the ascorbate peroxidase activity in ICE-L kept stable under the stress of UV-B radiation enhancement. The above experimental results indicated that the antioxidant enzyme system played an important role in the adaptation of Antarctic ice microalgae under the UV-B radiation change of Antarctic ecosystems.     

Induction of tolerance to oxidative stress in the green alga, Chlamydomonas reinhardtii, by abscisic acid

The effect of abscisic acid (ABA) on the tolerance to oxidative stress in a freshwater green alga, Chlamydomonas reinhardtii, was investigated. Exogenously added ABA enhanced the growth of this alga, which was observed under continuous illumination but not in the dark. The cells treated with ABA for 24 h showed tolerance to oxidative stress caused by exposure to paraquat or hydrogen peroxide. In the ABA‐treated cells, the activities of two antioxidant enzymes, catalase (CAT) and ascorbate peroxidase (APX), were significantly higher than those in the untreated control. The result suggests that ABA plays a role in the enhancement of tolerance to oxidative stress by increasing the activity of antioxidant enzymes.