NaCl induced cross-acclimation to UV-B radiation in four Barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) cultivars

The effect of pre-treatment with 200 mM NaCl on the response of four barley cultivars (Hordeum vulgare L. cv. Bülbül-89, Kalaycı-97, Tarm-92 and Tokak-157/37) to UV-B radiation was investigated. Salt stress as well as UV-B irradiation led to a decrease of the total chlorophyll (chl) content in all cultivars, except in Kalaycı-97. While carotenoids are almost not affected by NaCl treatment, UV-B irradiation caused an increase by 5–20% of carotenoid content of all cultivars. UV-B induced damages of photosynthetic apparatus were estimated by the rate of photosynthetic electron transport measured by chl fluorescence and the rate of oxygen evolution, the latter being more affected. Pre-treatment with NaCl alleviated harmful effect of UV-B irradiation on F _v/F _m and ETR, but not on oxygen evolution. UV-B-induced and UV-B-absorbing compounds with absorption at 300 and 438 nm increased as a result of UV-B treatment. The level of stress marker proline increased considerably as a result of NaCl treatment, while UV-B irradiation resulted in a pronounced increase of the level of H₂O₂. MDA enhanced in the seedlings subjected to salt and UV-B stress. Established cross-acclimation to UV-B as a result of salt treatment could be due to the increased free proline and the level of UV-B absorbing compounds in barley seedlings subjected to NaCl.     

Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. II. Time-course, comparison with flavonoid responses and adaptive significance

UV-B radiation inhibits hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order lo further characterize the response and gain insight into its potential ecological significance, the time-course of inhibition was measured and compared with the time-course of flavonoid accumulation in the same seedlings. When a background of strong (> 620 μmol m^?2 s^?1) white light (WL) was supplemented with low irradiance UV-B (～ 3 μmol m^?2 s^?1). substantial (～ 50%) inhibition of elongation occurred within 3 h of the light treatment. The magnitude of UV-B-induced elongation inhibition was similar in wild type (WT) and au-mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV-B on elongation, induction of flavonoid accumulation in WT and au seedlings undergoing de-etiolation was a much slower response. Several UV-absorbing compounds appeared to be specifically induced by light, and some of them accumulated faster under the WL + UV-B treatment than under WL alone. However, there was little or no delectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific UV-B effect was measurable only after 6 h of continuous treatment. Indeed. UV-B-screening properties of crude alcoholic extracts were not different between WL and WL + UV-B treatments until after 9 or 24 h. When the light treatments were applied to seedlings that were just breaking through the soil surface. UV-B was found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de-etiolating seedlings is an evolved response lo UV-B, which may serve to minimize seedling exposure to sunlight until protective pigmentation responses (triggered by WL and UV-B) have taken place in the seedlings epidermis.     

Physiological responses of wheat seedlings to drought and UV-B radiation. Effect of exogenous sodium nitroprusside application

Physiological and biochemical responses of wheat seedlings to drought, UV-B radiation, and combined stress were investigated. Drought, UV-B, and combined stresses retarded seedling growth by 26.5, 29.1, and 55.9%, respectively. One reason for growth retardation may be the oxidative damage indicated by an increase in the H₂O₂ content and lipid peroxidation degree. Furthermore, there was negative correlation between shoot fresh weight and H₂O₂ content, fresh weight and the content of thiobarbituric acid-reacting substances (TBARS), and the positive correlation between H₂O₂ content and TBARS (R ² = 0.9251, 0.9005, and 0.9007, respectively). The activities of superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase increased under drought, UV-B, and the combination of stresses, while catalase activity decreased under the combined stress as compared to the control. The combination of drought and UV-B caused more severe damage to wheat seedlings than stress factors applied separately. Thus, the combined application of drought and UV-B had more strong adverse effects on wheat seedlings. The addition of 0.2 mM sodium nitroprusside (SNP) enhanced wheat seedling growth under drought, UV-B, and combined stress, likely, due to decreasing the accumulation of H₂O₂ and lipid peroxidation as well as activating the antioxidant enzymes. However, SNP treatment decreased the proline content. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 5, pp. 763–769. The text was submitted by the authors in English.     

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.     

<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.     

Response of Barley Seedlings to UV-B Radiation as Affected by Proline and NaCl

Barley (Hordeum vulgare L. cv. Alfa) seedlings were treated for 4 d before UV-B irradiation with 0.05 mM proline or 150 mM NaCl. UV-B exposure induced synthesis of yellow coloured compounds with maximum absorbance at 438 nm. The content of these compounds was increased in proline-treated and decreased in NaCl-treated plants. UV-B radiation reduced chlorophyll/carotenoids ratio, oxygen evolution rate and photochemical efficiency of PS 2 as estimated by chlorophyll fluorescence and increased proline accumulation, H₂O₂ generation and lipid peroxidation. Exogenous proline had no effect on the parameters studied and did not change the response of plants to UV-B radiation. NaCl inhibited photochemical efficiency of PS 2, reduced oxygen evolution and increased H₂O₂ concentration and lipid peroxidation. The combination of NaCl and proline treatment led to lowering the inhibitory effect of NaCl in non UV-B irradiated seedlings. There was not relationship between the level of UV-B-induced compounds and UV-B tolerance of barley seedlings.     

UV-B response of green and etiolated barley seedlings

7-d-old etiolated and green barley seedlings (Hordeum vulgare L. cv. Alfa) were irradiated with UV-B for 30 min and then kept for 24 h in light or darkness. Chlorophyll (Chl) synthesis was inhibited by about 30 % as a result of UV-B irradiation, but there were no significant changes in photochemical activity measured by variable to maximum fluorescence ratio (F_v/F_m), quantum yield (Φ_PS2) and oxygen evolution rate. Electron transport of etiolated seedlings was similar to that of green ones, nevertheless, the Chl content was more then 2-fold lower. Ribulose-1,5-bisphosphate carboxylase/oxygenase large and small subunits were diminished as a result of UV-B irradiation in etiolated and green plants, especially in those kept in the darkness. Catalase activity decreased and total superoxide dismutase activity increased in green and etiolated plants following UV-B treatment. When benzidine was used as a substrate, an isoform located between guaiacol peroxidases 2 and 3 (guaiacol peroxidase X) appeared, which was specific for UV-B treatment. As a result of irradiation, the contents of UV-B absorbing and UV-B induced compounds increased in green seedlings but not in etiolated seedlings.     

UV-B辐射胁迫对杨桐幼苗生长及光合生理的影响

通过对UV-B辐射胁迫下亚热带典型木本杨桐幼苗的生长及光合生理的研究,探讨植物对于UV-B辐射胁迫的生理响应及适应性机理,进而揭示UV-B辐射变化对亚热带森林树种的影响.实验设置UV-B辐射滤光组、自然光对照组以及辐射增强组,选择亚热带典型树种杨桐(Cleyera japonica Thunb.)幼苗为实验材料.研究结果表明:(1)增强UV-B辐射会降低杨桐幼苗的叶绿素含量,而降低辐射则会显著促进叶绿素的增加,且这种胁迫在时间上具有积累性.(2)增强或降低辐射强度都会抑制杨桐地径的生长,增强辐射会产生更显著的抑制;降低辐射强度会对杨桐幼苗的株高生长产生促进作用,反之,则会抑制其生长.3个测定期数据综合分析显示随着处理时间的加长,这种胁迫作用有减小的趋势.(3)对光响应曲线的分析表明相对于自然光条件下的UV-B辐射,降低其强度对杨桐幼苗光合作用有显著的促进作用,反之则会抑制,不过抑制作用并不显著;对于光合特征参数的分析表明增强或降低UV-B辐射会显著降低杨桐幼苗的光饱和点(LSP)和光补偿点(LcP),而对最大净光合速率(Amax)、表观光合量子效率(AQY)、暗呼吸速率(Rd)影响均不显著,表明辐射胁迫对杨桐幼苗利用光能的效率影响不大,从而也并未对杨桐的光合作用产生显著性的伤害,但是由于森林树种的多年生特性,这种影响将是积累性的或延迟的,UV-B所造成的光合作用或光能利用率的微小变化都可能会积累成长期影响.因此,对森林树种进行长期研究是必要的.     

Silicon Improves the Tolerance of Wheat Seedlings to Ultraviolet-B Stress

Enhanced ultraviolet-B (UV-B) irradiation is one of the most important abiotic stresses that could influence the growth and physiological traits of plants. In this work, we reported the effects of silicon on the growth and physiological characteristics of wheat seedlings (Triticum aestivum L. cv Hengmai5229) subject to UV-B stress. Treatments with silicon significantly increased total biomass and chlorophyll (a + b) content, and reduced malondialdehyde (MDA) content and the rate of superoxide radical (O₂⁻) production in wheat seedlings subjected to UV-B stress. Silicon treatments also induced an increased in soluble sugar, anthocyanins, and flavonoid content. Leaf silicon concentration increased with the increasing of silicon supply to soil. Positive correlations were found in leaf silicon concentration with total biomass, chlorophyll (a + b), proline, and soluble protein content, respectively. MDA content and the rate of O₂⁻ production were negatively correlated with leaf silicon concentration in seedlings. The results demonstrated that silicon alleviated the damage caused by UV-B on wheat seedlings to some extent by the increase in antioxidant compounds content and leaf silicon concentration.     

Risposte Fotomorfogeniche Indotte Dalla Radiazione UV-B in Brassica Oleracea var. Capitata

Abstract

Photomorphogenic responses induced by UV-B radiation in Brassica oleracea var. capitata.—Ultraviolet radiation can induce a plethora of “damaging” and “non damaging” effects in higher plants. We analyzed two possible photomorphogenic responses to UV-B radiation, the anthocyanin accumulation and the inhibition of hypocotyl elongation by modifying the UV spectral range with specific cut-off filters, under two levels of photon fluence rate. Experimental results suggest that detrimental effects are due to shorter wavelenghts of UV-B region (less than 305 nm); in contrast some adaptative responses may be induced by longer wavelenghts of UV-B region (between 305 and 320 nm). We attempted to determine the involvment of endogenous anthocyanin content in the UV-B photoprotection. Our experiments suggest a secondary role of anthocyanin accumulation in UV-B plant adaptation.     

滤除自然光中UV-B辐射成分对高山植物美丽风毛菊光合生理的影响

采用滤除自然光谱中UV-B辐射成分的方法, 探讨了高山植物美丽风毛菊(Saussurea superba)光合机构对青藏高原强UV-B辐射的响应和适应特性。结果表明, 强太阳光中的UV-B成分能引起净光合速率的降低。连续16天不同天气下的观测表明, 滤除UV-B处理时3 min暗适应的光化学量子效率有升高的趋势; 晴天下稳态光化学效率的分析也显示滤除UV-B处理的实际光化学量子效率和光化学猝灭系数有升高趋势, 意味着自然光中的UV-B成分可限制美丽风毛菊叶片PSII反应中心的激发能捕获效率。PSII有效光化学量子效率的增加和非光化学猝灭系数的降低进一步表明, UV-B辐射能导致有效光化学效率的降低和非光化学能量耗散的增加。由上可知, 自然强UV-B辐射是限制美丽风毛菊叶片光合作用的一个因素。滤除UV-B辐射处理对光合色素含量的影响较小, 无论以叶面积还是叶鲜重为基础的滤除UV-B处理仅有微弱的增加趋势, 说明强UV-B辐射具有加速光合色素的光氧化进程, 促进细胞成熟和叶片衰亡的潜在作用。同样UV-B吸收物质的含量也几乎没有变化, 表明强太阳辐射环境下生活的高山植物美丽风毛菊叶表皮层中已具有较多的紫外线屏蔽物质, 足以抵御目前环境中强太阳UV-B辐射可能引起的伤害, 较少受UV-B辐射波动的影响。     

Responses in growth,physiology and nitrogen nutrition of dragon spruce (<Emphasis Type="Italic">Picea asperata</Emphasis>) seedlings of different ages to enhanced ultraviolet-B

In the southeast of the Qinghai–Tibetan Plateau of China, dragon spruce (Picea asperata) is a key species and widely used in reforestation processes in the area. The paper mainly studied the effects of ultraviolet-B (UV-B) on growth, physiology and nitrogen nutrition of 3- and 6-year-old dragon spruce seedlings. The experimental design included ambient UV-B (control) and enhanced UV-B (+UV-B, a 30% increase). Enhanced UV-B significantly decreased growth, needle and root nitrogen concentration, needle nitrate reductase activity and increased UV-B absorbing compounds and malondialdehyde (MDA) content of two old dragon spruce seedlings. Glutamine synthetase activity was not affected by enhanced UV-B in two old dragon spruce seedlings. On the other hand, different old seedlings also exhibited different physiological responses to enhanced UV-B radiation. Chlorophyll content, carotenoids content and soluble protein content in 3-year-old seedlings significantly reduced by enhanced UV-B, but those in 6-year-old seedlings were not affected by enhanced UV-B. Proline content of 6-year-old seedlings were increased by enhanced UV-B. Compared with the 3-year-old seedlings, the 6-year-old seedlings showed lower reduction of growth and MDA content, and accumulated more proline and UV-B absorbing compounds for protecting seedlings under enhanced UV-B. The results implicated that 3-year-old seedlings were more sensitivity to enhanced UV-B than 6-year-old seedlings.     

Some effects of enhanced UV-B irradiation on the growth and composition of plants

Barley (Hordeum vulgare), corn (Zea mays), bean (Phaseolus vulgaris), and radish (Raphanus sativus) seedlings were continuously irradiated under a lighting device for 5–10 d at an increased ultraviolet (UV)-B fluence rate. In their growth parameters, composition, and leaf surface, these four species responded differently to the increased UV-B exposure. Bean seedlings suffered the most serious effects, radish and barley less, and corn was hardly influenced at all. In all plant species, the fresh weight, the leaf area, the amounts of chlorophylls, carotenoids and the galactolipids of the chloroplasts were reduced. The lipid content of the corn and bean seedlings also diminished. But all the irradiated plants showed a rise in their protein content compared to the control plants. The content of flavonoids increased in barley and radish seedlings by about 50%. The effects on growth parameters and composition were more extensive with increasing UV-B fluence rates, at least as shown in the case of barley seedlings. The fresh weights fell proportionally with the chlorophylls and carotenoids. In contrast, the flavonoid content of barley leaves rose parallel to the increasing UV-B fluence rates and reached 180% of the value in the control plants with the highest UV-B fluence rate. Scorching appeared regularly in the form of bronze leaf discoloration at the highest UV-B fluence rates. Scanning electron micrographs of the leaf surface of UV-B irradiated plants showed deformed epidermal structures.Abbreviations MGDG monogalactosyldiglyceride - DGDG digalactosyldiglyceride - SL sulfoquinovosyldiglyceride - PG phosphatidylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - LA leaf are - FW fresh weight - DW dry weight - SEM scanning electron microscopy - C total carotenoids - Chl total chlorophyll     

Enhancement in leghemoglobin content of root nodules by exclusion of solar UV-A and UV-B radiation in soybean

The impact of exclusion of solar UV-B (280–320 nm) and UV-A+B (280–400 nm) radiation on the root nodules was studied in soybean(Glycine max var. MACS 330). Soybean plants were grown in the tropical region of Indore (Latitude-22.4°N), India under field conditions in metal cages covered with polyester exclusion filters that specifically cut off UV-B (<320 nm) and UV-A+B (<400 nm) radiation; control plants were grown under ambient solar radiation. Leghemoglobin content was analyzed in the root nodules on the 50^th day after emergence of seedlings. Exclusion of UV radiations significantly enhanced the leghemoglobin content in the nodules on fresh weight basis; 25% and 45% higher amount of leghemoglobin were present in the nodules after the exclusion of UV-B and UV-A+B radiation respectively. Analysis by native and SDS-PAGE showed high intense bands of leghemoglobin after the exclusion of UV-A+B as compared to control. Exclusion of UV radiation also enhanced the growth of roots as well as aerial parts of the plants. UV Exclusion increased nodulation by increase in the number and size of nodules. The results are discussed in the light of advantage of exclusion for enhancing protein/nitrogen content in the plants.     

Superoxide dismutase production by Isaria fumosorosea on metals and its role in stress tolerance and fungal virulence

Superoxide dismutase (SOD) is an anti-oxidant enzyme which also plays a role in fungal virulence. The present study was conducted to elucidate its role in fungal infection and stress tolerance of entomopathogenic fungi, Isaria fumosorosea. SOD activity of I. fumosorosea conidia differed significantly on the growth medium supplemented with different metal compounds. The use of Cu + Zn proved to be the most active inducer of SOD activity. Cu + Zn treatment enhanced the fungal tolerance to oxidative stress generated by menadione in the medium (0–3 mM) as evaluated by colony growth. The conidial tolerance to UV-B radiation and heat was evaluated by assays of spore germination. Conidia produced on cultures with Cu + Zn were more tolerant to UV-B and thermal stress as well as exhibiting a higher rate of virulence against P. xylostella larvae. Our study highlights that SOD contributes significantly to the virulence and stress tolerance of I. fumosorosea and reveals possible means to improving field persistence and efficacy of a fungal formulation by manipulating the antioxidant enzymes of fungal pathogens.     

Antioxidant Capacity of Flavonoid in Soybean Seedlings under the Joint Actions of Rare Earth Element La(III) and Ultraviolet-B Stress

The dynamic state of antioxidant capacity of flavonoid was investigated for a further demonstration of alleviating the damage of the ultraviolet (UV)-B radiation in the La-treated soybean seedlings under UV-B stress. Using hydroponics culture, the effects of lanthanum on the contents of flavonoid and its ability of antioxidant under elevated ultraviolet-B radiation (280–320 nm) was studied. The results showed flavonoid content in soybean seedlings with UV-B treatment during the stress and convalescent period was increased initially and then decreased, compared with control. Membrane permeability and MDA contents increase at first (first to fifth day) and then decrease (6th–11th day). A similar change of flavonoid content and clearance of flavonoid scavenging and ·OH in soybean seedlings occurred. Flavonoid content and ability of flavonoid scavenging and ·OH in soybean seedlings with La(III) + UV-B treatment were higher than those of UV-B treatment. Meanwhile, membrane permeability and MDA contents in soybean seedlings were lower than those of UV-B treatment. Compared with control, phenylalanine content in soybean seedlings with UV-B treatment is depressed, phenylalanine content in soybean seedlings with La(III) treatment was enhanced. However, phenylalanine content in La(III) + UV-B treatment is not decreased but slightly increased, compared with UV-B treatment. It suggested that the regulative effect of La(III) of the optimum concentration on flavonoid improved the metabolism of ROS, diminished the concentration of MDA and maintained normal plasma membrane permeability, and that its protective effect against low UV-B radiation is superior to that of high UV-B radiation. The defensive effect of La(III) on soybean seedlings under UV-B stress is carried out on the layer of defense system.     

Changes in leaf expansion and epidermal screening effectiveness in Liquidambar styraciflua and Pinus taeda in response to UV-B radiation

Absorption or screening of ultraviolet-B (UV-B) radiation by the epidermis may be an important protective method by which plants avoid damage upon exposure to potentially harmful UV-B radiation. In the present study we examined the relationships among epidermal screening effectiveness, concentration of UV-absorbing compounds, epidermal anatomy and growth responses in seedlings of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.). Seedlings of each species were grown in a greenhouse at the University of Maryland under either no UV-B radiation or daily supplemental UV-B radiation levels of 4, 8 or 11 kJ m^?2 of biologically effective UV-B (UV-B_BE) radiation. Loblolly pine seedlings were subsequently grown in the field under either ambient or supplemental levels of UV-B radiation. At the conclusion of the growing season, measurements of epidermal UV-B screening effectiveness were made with a fiber-optic microprobe. In loblolly pine, less than 0.5% of incident UV-B radiation was transmitted through the epidermis of fascicle needles and about 1% was transmitted in primary needles. In contrast, epidermal transmittance in sweetgum ranged from about 20% in leaves not preconditioned to UV-B exposure, to about 10% in leaves grown under UV-B radiation. The concentration of UV-absorbing compounds was unaffected by UV-B exposure, but generally increased with leaf age. Increases in epidermal thickness were observed in response to UV-B treatment in loblolly pine, and this accounted for over half of the variability in UV-B screening effectiveness. In spite of the low levels of UV-B penetration into the mesophyll, delays in leaf development (both species) and final needle size (loblolly pine) were observed. Seedling biomass was reduced by supplemental UV-B radiation in loblolly pine. We hypothesize that the UV-induced growth reductions were manifested by changes in either epidermal anatomy or epidermal secondary chemistry that might negatively impact cell elongation.     

Responses of Wheat Roots to Exogenous Selenium Supply Under Enhanced Ultraviolet-B

Effects of selenium (Se) on growth and some physiological traits of roots in wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress are reported. Responses of roots were different depending on the Se concentration. Compared with the control, root weight of wheat seedlings treated with 1.0 and 2.0 mg Se kg⁻¹ soil increased by 39.47% and 16.28%, respectively. The lower amount Se (0.5 mg kg⁻¹) and the higher amount Se treatments (3.0 mg kg⁻¹) did not significantly affect on root weight. Se treatments significantly increased root activity, flavonoids and proline content, and activities of peroxidase and superoxide dimutase in wheat roots exposed to enhanced UV-B. In addition, the treatments with 0.5, 1.0, and 2.0 mg Se kg⁻¹ significantly reduced malondialdehyde content and the rate of superoxide radical (O₂⁻) production of roots, whereas the higher amount Se treatment only induced a decrease in the rate of O₂⁻ production. The results of this study demonstrated that optimal Se supply promoted roots growth of wheat seedlings, and that optimal Se supply could reduce oxidative stress in wheat roots under enhanced UV-B radiation.     

Antioxidant Responses of Wheat Seedlings to Exogenous Selenium Supply Under Enhanced Ultraviolet-B

The paper reports the effects of selenium (Se) supply on growth and antioxidant traits of wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress. Antioxidant responses of seedlings were different depending on the Se concentration. Compared with the control, the lower amount used (0.5 mg Se kg⁻¹ soil) had no significant effect on biomass accumulation. The treatments with 1.0, 2.0, and 3.0 mg Se kg⁻¹ promoted biomass accumulation of wheat seedlings, and the increased amount in biomass was the most at 1.0 mg Se kg⁻¹ treatment. Se treatments with 1.0, 2.0, and 3.0 mg kg⁻¹ also significantly increased activities of peroxidase (POD) and superoxide dismutase (SOD) and reduced the rate of superoxide radical (O₂⁻) production and malondialdehyde (MDA) content of wheat seedlings. In addition, anthocyanins and phenolic compounds content in wheat seedlings evidently increased by the treatments with 1.0 and 2.0 mg Se kg⁻¹. The lower Se treatment had no significant effect on MDA content, although it increased activities of antioxidant enzymes (POD, SOD, and catalase activities) and reduced the rate of O₂⁻ production in wheat seedlings. These results suggest that optimal Se supply is favorable for the growth of wheat seedlings and that optimal Se supply can reduce oxidative stress of seedlings under enhanced UV-B radiation.     

Carbon and nitrogen partitioning in the freshwater submerged macrophyte <Emphasis Type="Italic">Vallisneria gigantea</Emphasis> in response to ultraviolet-B irradiance

The aim of this study was to determine the effect of ultraviolet-B (UV-B) exposures (0.55 and 1.1 W m⁻²) on the distributional variations of plant carbon and nitrogen content in both below- and aboveground parts in Vallisneria gigantea Graebner in laboratory conditions for a 3-month period. Plant biomass, total organic nitrogen, total organic carbon, lignin, water soluble carbohydrates and chlorophyll a and b were analysed and compared using repeated measures of analysis of variance (ANOVA) between UV-B-exposed and nonexposed treatments. A significant reduction (F _{(2, 15)} = 754.5, P < 0.001) was observed in leaf chlorophyll a concentrations at UV-B exposure levels. In the high UV-B irradiation group, a significant decrease (50.3%) was observed compared with the initial aboveground biomass. The total organic nitrogen content at both high and low UV-B exposure levels declined significantly by 25.6% and 24.3%, respectively, in aboveground samples, while significant increases of 39.6% and 40%, respectively, were observed in belowground tissues, compared with non-UV-B treatment groups. The partitioning of total organic carbon in the aboveground tissues was reflected by significant increase in lignin and water soluble carbohydrates in aboveground tissues under UV-B stress. However, total organic nitrogen demonstrated greater partitioning into the belowground tissues of V. gigantea. This study highlights the defense mechanisms of V. gigantea through changes in the percentage composition of carbon and nitrogen compounds with negative effects on nutrient regeneration, which can be accelerated in a system exposed to UV-B irradiation at or above biologically effective levels.