Effect of Cerium on Photosynthetic Pigments and Photochemical Reaction Activity in Soybean Seedling Under Ultraviolet-B Radiation Stress

Effects of cerium (Ce) on photosynthetic pigments and photochemical reaction activity in soybean (Glycine max L.) under ultraviolet-B (UV-B) radiation stress were studied under laboratory conditions. UV-B radiation caused the decrease in chlorophyll content, net photosynthetic rate, Hill reaction activity, photophosphorylation rate and Mg²⁺-ATPase activity. Ce (III) (20 mg L⁻¹) could alleviate UV-B-induced inhibition to these photosynthetic parameters because values of these photosynthetic parameters in Ce (III) + UV-B treatment were obviously higher than those with UV-B treatment alone. Dynamic changes of the above photosynthetic parameters show that Ce (III) could slow down the decrease rate of these photosynthetic parameters during a 5-day UV-B radiation and quicken the restoration during recovery period. The final restoration degree of five parameters mentioned above in leaves exposed to low level of UV-B radiation (0.15 W m²) was higher than that exposed to high level (0.45 W m²). Correlating net photosynthetic rate with other four parameters, we found that the regulating mechanisms Ce (ΠΙ) on photosynthesis under various level of UV-B radiation were not the same. The protective effects of Ce (III) on photosynthesis in plants were influenced by the intensity of UV-B radiation.     

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.     

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.     

Photosynthetic and biochemical characterization of pigments and UV-absorbing compounds in <Emphasis Type="Italic">Phormidium tenue</Emphasis> due to UV-B radiation

We report the effect of UV-B radiation (0.8 ± 0.1 mW cm⁻²) and UV-B radiation supplemented with low-intensity PAR (∼80 μmol photons m⁻² s⁻¹) on the photosynthesis, photosynthetic pigments, phosphoglycolipids, oxidative damage, enzymatic antioxidants, and UV-absorbing compounds in Phormidium tenue, a marine cyanobacterium. UV-B radiation resulted in a decline in photosynthesis and photosynthetic pigments leading to lower biomass. P. tenue synthesized UV-absorbing compounds like mycosporine-like amino acids (MAAs) and scytonemin in response to UV-B radiation. Quantity of MAAs and scytonemin was higher when UV-B was supplemented with low-level PAR. UV-B treatment also resulted in quantitative changes in phosphoglycolipids of the membrane. The UV-B treatment resulted in a slight increase in the level of peroxidation of cell membrane and very little increase in the activity of superoxide dismutase (SOD). Results indicate that UV-B affected photosynthesis and that the main protective system was the synthesis of MAAs and scytonemin-like compounds rather than antioxidant enzymes such as SOD.     

Protective Effect of Rare Earth Against Oxidative Stress Under Ultraviolet-B Radiation

The effects of lanthanum (III) (La(III)) in protecting soybean leaves against oxidative stress induced by ultraviolet-B (UV-B) radiation were investigated. The increase in contents of hydrogen peroxide (H₂O₂) and superoxide () due to UV-B radiation suggested oxidative stress. The increase in the content of malondialdehyde (MDA) and the decrease in the index of unsaturated fatty acid (IUFA) indicated oxidative damage on cell membrane induced by UV-B radiation. La(III) partially reversed UV-B-radiation-induced damage of plant growth. The reduction in the contents of H₂O₂, , and MDA and increase in the content of IUFA, compared with UV-B treatment, also indicated that La(III) alleviated the oxidative damage induced by UV-B radiation. The increase in the activities of superoxide dismutase and peroxidase and the contents of ascorbate, carotinoids, and flavonoids were observed in soybean leaves with La(III) + UV-B treatment, compared with UV-B treatment. Our data suggested that La(III) could protect soybean plants from UV-B-radiation-induced oxidative stress by reacting with reactive oxygen species directly or by improving the defense system of plants.     

Effects of quercetin and enhanced UV-B radiation on the soybean (Glycine max) leaves

The possible ameliorative effects of quercetin on soybean [Glycine max (L.) Merr.] leaves exposed to UV-B radiation were conducted in greenhouse. The symmetrical leaves supplied with quercetin solution (0.2%, 1%) were exposed to UV-B radiation (0, 3.5, 6.5 kJ m⁻² d⁻¹). 0.2% quercetin ameliorated leaf photosynthesis, improved leaf water content (LWC), and decreased lipid oxidation. The unfavorable effect on photosynthetic parameter was displayed in 1% quercetin treatment. The effect of quercetin on phenylalanine ammonia lyase (PAL) activity varied with the quercetin concentration, UV-B radiation intensity and leaf development. In the later development polyphenol oxidase (PPO) activity was increased significantly by quercetin treatments. We suggested that quercetin with suitable concentration could serve as UV-B protective agent partly due to its antioxidant capacity.     

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.     

The interactive effect of water deficit and UV-B radiation on salicylic acid accumulation in barley roots and leaves

The aim of the paper was to determine the effect of water deficit (WD) and UV-B radiation acting individually and in combination on salicylic acid (SA) accumulation as well as on the activity of phenylalanine ammonia-lyase (PAL) and benzoic acid hydroxylase (BA2H) that control its biosynthetic route from phenylalanine. An additional aim was to test whether the interaction of these stresses limits the negative effect of a single stress on tissue hydration and membrane injury. Two-week-old seedlings were subjected to water deficit (WD), UV-B irradiation (UV-B) and three different combinations of WD and UV-B: (I) WD and UV-B applied at the same time, (II) UV-B applied before WD, and (III) WD applied before UV-B. Water deficit was imposed by immersing the root system in aerated nutrient solution with polyethylene glycol (PEG 6000) of water potential – 0.5 MPa. UV-B dosage was 24 kJ m⁻² day⁻¹ (0.84 W m⁻²) at the canopy level. UV-B and WD imposed individually and jointly, caused, in a time-dependent manner, an increase in SA content in both organs. Increased levels of SA in WD stressed plants were accompanied by an increase in the activity of PAL and BA2H. However, in plants exposed to UV-B were accompanied only by an increase in the activity of BA2H. Under WD conditions, an earlier increase of SA content was observed in roots than in leaves, which may indicate the involvement of SA in the signal transduction between roots and leaves. In plants exposed to sequential action of WD and UV-B, regardless of the order of its imposition, the effect of each single factor on SA accumulation in leaves was strengthened. WD had a greater effect on water loss and membrane injury than UV-B radiation. In plants exposed to WD after pre-treatment with UV-B radiation, a cross-tolerance mechanism was observed. Leaves of these plants did not show increased lipid peroxidation, measured in terms of malondialdehyde content, and a decrease in water content. This protective action was probably caused by the increase of the SA level in leaves of the UV-B treated plants prior to WD imposition.     

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.     

Photosynthetic responses to solar UV-A and UV-B radiation in low-and high-altitude populations of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis>

Two contrasting sea buckthorn (Hippophae rhamnoides L.) populations from the low (LA) and high (HA) altitudinal regions were employed to evaluate the plant physiological responses to solar UV-A radiation and near-ambient UV-B radiation (UV-B+A) under the sheltered frames with different solar ultraviolet radiation transmittance. LA-population was more responsive to solar UV-A. Some modification caused by UV-A only existed in LA-population, such as significant reduction of leaf size, relative water content, and chlorophyll (Chl) b content as well as δ¹³C elevation, coupled with larger increase of contents of total carotenoids (Cars). This higher responsiveness might be an effective pre-acclimation strategy adapting for concomitant solar UV-B stress. Near-ambient UV-B+A radiation caused significant reduction of leaf size and Chl content as well as slight down-regulation of photosystem 2 activity that paralleled with higher heat dissipation, while photosynthetic rate was modestly but significantly increased. The higher photosynthesis under near-ambient UV-B+A radiation could be related to pronounced increase of leaf thickness and effective physiological modification, like the increase of leaf protective pigments (Cars and UV-absorbing compound), constant high photochemical capacity, and improved water economy.     

Ultraviolet-B and water stress effects on growth,gas exchange and oxidative stress in sunflower plants

The effects and interaction of drought and UV-B radiation were studied in sunflower plants (Helianthus annuus L. var. Catissol-01), growing in a greenhouse under natural photoperiod conditions. The plants received approximately 1.7 W m(-2) (controls) or 8.6 W m(-2) (+UV-B) of UV-B radiation for 7 h per day. The UV-B and water stress treatments started 18 days after sowing. After a period of 12 days of stress, half of the water-stressed plants (including both UV-B irradiated or non-irradiated) were rehydrated. Both drought and UV-B radiation treatments resulted in lower shoot dry matter per plant, but there was no significant interaction between the two treatments. Water stress and UV-B radiation reduced photosynthesis, stomatal conductance and transpiration. However, the amplitude of the effects of both stressors was dependent on the interactions. This resulted in alleviation of the negative effect of drought on photosynthesis and transpiration by UV-B radiation as the water stress intensified. Intercelluar CO(2) concentration was initially reduced in all treatments compared to control plants but it increased with time. Photosynthetic pigments were not affected by UV-B radiation. Water stress reduced photosynthetic pigments only under high UV-B radiation. The decrease was more accentuated for chlorophyll a than for chlorophyll b. As a measure for the maximum efficiency of photosystem II in darkness F (v)/F (m) was used, which was not affected by drought stress but initially reduced by UV-B radiation. Independent of water supply, UV-B radiation increased the activity of pirogalol peroxidase and did not increase the level of malondialdehyde. On the other hand, water stress did not alter the activity of pirogalol peroxidase and caused membrane damage as assessed by lipid peroxidation. The application of UV-B radiation together with drought seemed to have a protective effect by lowering the intensity of lipid peroxidation caused by water stress. The content of proline was not affected by UV-B radiation but was increased by water stress under both low and high UV-B radiation. After 24 h of rehydration, most of the parameters analyzed recovered to the same level as the unstressed plants.     

Comparison of polyethylene glycol 3350 induced osmotic stress and soil drying for drought simulation in three woody species

 Drought simulation usually involves either soil drying or the use of an osmoticum, such as high molecular weight (>3000) polyethylene glycol (PEG). Although easy to apply, PEG absorption and toxicity remain a concern. This study compared the effects of soil drying and use of an osmoticum (PEG 3350). Osmotic stress and soil drought were applied to 5-month-old seedlings of jack pine (Pinus banksiana Lamb.) and black spruce [Picea mariana (Mill) B.S.P.] , which are both coniferous species from cold, boreal regions of North America, and flooded gum (Eucalyptus grandis W. Hill ex Maiden), a hardwood species growing in warmer, sub-tropical regions of Australia. Results showed that PEG 3350 was absorbed by roots, transported to shoots, and deposited on the leaves of both flooded gum and jack pine (but not black spruce). PEG lowered relative water content and damaged leaf tissues in both species, and also damaged stomata of flooded gum. Although 12 days of PEG-induced osmotic stress produced a decline in water potentials that was similiar to soil drying, it also caused significantly higher membrane injury and reduced net photosynthesis and stomatal conductance in leaves of all three species. Recovery of net photosynthesis and stomatal conductance in PEG-treated jack pine and black spruce was also slower after stress alleviation. Even a short exposure to PEG 3350 adversely affected seedlings compared to soil drought. These results confirmed that drought effects may vary, depending on the species and the method of stress induction. Received: 6 March 1996 / Accepted: 17 September 1996     

Response of barley seedlings to water deficit and enhanced UV-B irradiation acting alone and in combination

Responses of barley seedlings to water deficit (WD) induced by polyethylene glycol (PEG 6000) and ultraviolet (UV-B; 280–320 nm) radiation and their interaction (UV-B + WD) were examined. A decrease in dry matter yield and water content of leaves and roots was observed following application of WD and UV-B + WD, while no changes were found after treating barley plants with UV-B. Proline content was increased in leaves under WD conditions and UV-B + WD. In contrast, UV-B treatment had no effect on the accumulation of proline in leaves of barley plants. Changes in root proline content showed a varied response: WD induced an increase in the level of this amino acid, while UV-B as well as UV-B + WD suppressed root proline content. The lipid peroxidation product malondialdehyde (MDA) was increased in leaves under WD and UV-B + WD stresses. Root MDA content increased in WD-stressed plants, but it decreased in the case of combined application of both stresses. The applied stress factors operated in a variable manner on phenylpropanoid metabolism. Phenylalanine ammonia-lyase (PAL) activity in leaves and roots was stimulated after exposure to WD and application of UV-B + WD stresses, while UV-B stress did not affect its activity. On the other hand, UV-B treatment enhanced the activity of 4:coumarate-CoA ligase (4CL) in leaves and this enhancement was positively correlated with the accumulation of anthocyanins and flavonols. However, the combined application of WD and UV-B reduced the positive effect of UV-B on the accumulation of these compounds and the activity of 4CL. Surprisingly, anthocyanins and flavonols were not detected in roots of examined barley seedlings despite increased 4CL activity. The results suggest that UV-B-induced activation of 4CL as well as accumulation of anthocyanin and flavonols in leaves is beneficial for the response to this stress factor. On the other hand, WD-induced reduction of the effect of UV-B on 4CL activity and the contents of anthocyanin and flavonol might be a cause of membrane damage in UV-B- and WD-stressed plants. In addition, conversely to what could be expected, the UV-B effect was perceived by the water-stressed roots, which exhibited reduced lipid peroxidation (MDA) and proline accumulation in WD-stressed plants exposed to UV-B.     

Evaluation of the different levels of variability in the underwater light field of a shallow estuary

The underwater light climate of a shallow estuary located at the southern coast of the Baltic Sea has been investigated, with special emphasis on the spectral irradiance composition and on short-term irradiance fluctuations caused by vertical mixing and wave focussing. The inherent optical properties of the water body were dominated by phytoplankton pigment absorption in the long-wavelength range and by coloured, dissolved organic matter (cDOM) absorption in the wavelength range <500 nm, including ultraviolet-A (UV-A) and ultraviolet-B radiation (UV-B). Pronounced particulate scattering combined with the absorption values to give very high attenuation coefficients, especially for the shorter wavelengths of UV-B radiation. Photosynthetically active radiation (PAR) was found to be reduced to 1% of the surface value within 0.8 m in the inner, hypertrophic end of the estuary and within 1.9 m in the outer, eutrophic parts of this system, with corresponding 1% penetration depths for UV-B of 0.13 and 0.31 m. During late winter and early spring, the period when reduced atmospheric ozone concentrations and enhanced UV-B have been reported over northern Europe, the irradiance levels in the water column were greatly reduced, due to strong attenuation by ice cover and overlying snow. cDOM concentration of the water was also found to remain at a high level during these periods, and indeed throughout the year, thus reducing the exposure of organisms to UV-R and PAR still further. A complex irradiance regime was found in this system, with irregular and high amplitude fluctuations caused by wind-induced vertical mixing and wave focussing being superimposed upon the solar-angle-dependent seasonal and daily cycles. The methods used to quantify the short-term fluctuations are described, and their relevance to phytoplankton physiology is discussed. The wave-focussing effect is unique to the aquatic environment, and measurements showed that average subsurface irradiances could be increased by up to 5 times for periods lasting for <1 s. The highest irradiances recorded during wave-focussing events reached over 9,000 μmol photons m^–2 s^–1. Received in revised form: 7 April 2000 Electronic Publication     

The effects of enhanced ultraviolet-B and nitrogen supply on growth,photosynthesis and nutrient status of <Emphasis Type="Italic">Abies faxoniana</Emphasis> seedlings

Abies faxoniana is a key species in reforestation processes in the southeast of the Qinghai-Tibetan Plateau of China. The changes in growth, photosynthesis and nutrient status of A. faxoniana seedlings exposed to enhanced ultraviolet-B (UV-B), nitrogen supply and their combination were investigated. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ m⁻² day⁻¹; enhanced UV-B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (0; 20 g N m⁻²). The results indicated that: (1) enhanced UV-B significantly caused a marked decline in growth parameters, net photosynthetic rate (Pn), photosynthetic pigments and F _v/F _m, (2) supplemental nitrogen supply increased the accumulation of total biomass, Pn, photosynthetic pigments and F _v/F _m under ambient UV-B, whereas supplemental nitrogen supply reduced Pn, and not affect biomass under enhanced UV-B, (3) enhanced UV-B or nitrogen supply changed the concentration of nutrient elements of various organs.     

Gas exchange,chlorophyll fluorescence,and osmotic adjustment in two mango cultivars under drought stress

The responses of photosynthetic gas exchange, chlorophyll fluorescence, content of pigments, main osmolytes, and malondialdehyde (MDA) to water-withholding for 15 days and re-hydration in seedlings of two mango cultivars (Mangifera indica L. var. “Choke Anand’ and var. “Khieo Sawoei”) under 50% sunlight and full sunlight were investigated. For both cultivars, the water-witholding resulted in progressively decreases in leaf relative water content, net photosynthesis (P _n), stomatal conductance (g _s), and increases in the conversion of xanthophyll cycle pigments estimated by an index of leaf spectral reflectance (ΔPRI), carotenoid to chlorophyll ratio, non-photochemical quenching (NPQ), the contents of malondialdehyde (MDA) and compatible solutes (total soluble sugar and proline). The effect of the water stress was more pronounced in full sunlight than 50% sunlight. The maximum photochemistry efficiency measured at dawn was fairly constant during the period of the treatment for both cultivars under both light regimes. The water stress caused less pronounced inhibition of photosynthesis in “Choke Anand” than in “Khieo Sawoei” cultivar under both light regimes. After re-hydration, the recovery was relatively quicker in “Choke Anand” than in “Khieo Sawoei” cultivar. Both cultivars in both 50% and full sunlight showed complete recovery in photochemistry after 5 days of re-watering but photosynthesis did not show a complete recovery as indicated by gas exchange rates. As the results of lower NPQ, ΔPRI and osmotic adjustment in the cultivar “Khieo Sawoei” compared to the cultivar “Choke Anand”, the former cultivar was less tolerant to drought than the latter. Our study further showed that partial shading (e.g., 50% of sunlight) significantly alleviated the harmful effect of drought stress on mango cultivars but in fact stomata of seedlings grown in partial shade was more responsive to water deficit than in full light.     

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.     

UV-susceptibility of zoospores of the brown macroalga Laminaria digitata from Spitsbergen

The UV-susceptibility of zoospores of the lower sublittoral kelp Laminaria digitata was studied in the laboratory under varying fluence of spectral irradiance consisting of photosynthetically active radiation (PAR, 400–700 nm; = P), PAR + UV-A radiation (UV-A, 320–400 nm; = PA), and PAR + UV-A + UV-B radiation (UV-B, 280–320 nm; = PAB). In vivo absorption of phlorotannin, localisation of phlorotannin-containing physodes, structural changes, DNA damage and repair, photosynthesis and germination of zoospores were measured after exposure treatments and after 2–6 days of recovery in dim white light. Photodegradation of phlorotannins was observed after extended exposure to ultraviolet radiation (UVR). The UV-protective function of extra- and intracellular phlorotannins was, therefore, observed only after 8 h, but not after 16-h UVR exposure. The energetic cost of photoprotection may have caused the delay in ontogenic development of zoospores after 8-h exposure to PA and PAB treatment; longer exposure time corresponding to 16-h PA and PAB treatment eventually lead to cell degeneration at 6 days post-cultivation. The formation of cyclobutane–pyrimidine dimers (CPDs), as indicator of DNA damage, was not blocked by the UV-absorbing phlorotannins during the 16-h PAB exposure and the inability for DNA damage repair was likely responsible for low photosynthetic recovery and spore mortality. The higher sensitivity of L. digitata zoospores to UVR compared to other kelps such as Saccorhiza dermatodea and Alaria esculenta confirmed our hypothesis that the depth distribution of adult sporophytes in the field correlates to the sensitivity of their corresponding early life history stages to different stress factors in general and UVR in particular.     

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.     

Raffinose in seedlings of winter vetch (<Emphasis Type="Italic">Vicia villosa</Emphasis> Roth.) under osmotic stress and followed by recovery

During germination of winter vetch (Vicia villosa Roth.) seeds, the degradation of raffinose family oligosaccharides and galactosyl pinitols occurred faster in axis than in cotyledons. After 7 days of germination, all α-d-galactosides disappeared and the soluble carbohydrates in seedling tissues consisted of d-pinitol, sucrose, fructose, glucose and myo-inositol. Osmotic stress caused by incubation of seedlings in PEG 8000 solution (−0.5, −1.0, and −1.5 MPa) for 48 h induced the activity of crucial enzymes of the RFOs pathway, i.e. galactinol synthase and raffinose synthase, in both the root and epicotyl but not in cotyledons. The root and epicotyl accumulated elevated amounts of galactinol and raffinose as the osmotic potential was lowered. This process was transient because when PEG solution was replaced with water, galactinol and raffinose were degraded, thus confirming their direct involvement in the response of tissues to osmotic stress. Among other soluble carbohydrates, only sucrose accumulated in response to stress. The results did not show potential role of d-pinitol in the adjustment of winter vetch seedlings to osmotic stress.