Root morphology, root-hair development and rhizosheath formation on perennial grass seedlings is influenced by soil acidity

Cadmium (Cd) exerts a detrimental effect on the metabolism of plants, whereas selenium (Se) may protect them against various stressors through its antioxidative activity. In this in vitro study we investigated the impact of Se (2 µM Na₂SeO₄) on the growth, nutrient (P, S, K, Ca, Mg, B, Mn, Fe and Zn) concentrations and cell integrity of rape (Brassica napus oleifera) and two wheat (Triticum aestivum) genotypes subjected to Cd stress (600 µM CdCl₂). Rape accumulated both Cd and Se more than did wheat. In all plants, Cd markedly reduced the biomass, enhanced lipid peroxidation and diminished plasmalemma fluidity. A drop in the K uptake and the reduced plasmalemma permeability diminished the K efflux from the leaf cells. In contrast, Cd elevated S concomitantly with Zn, indicating an activity of detoxifying SH groups and SOD isoenzymes. When added alone, Se promoted the growth of all plants, it enhanced the accumulation of S, but the impact on other nutrients remained minor. In Cd-stressed plants, Se tended to counterbalance the Cd-induced changes in nutrients, it also reduced the lipid peroxidation and exerted positive effects on the cell membrane stability. The Cd stress and the protective role of Se were most evident in rape. The Finnish wheat genotype was less tolerant to Cd than the Polish one.     

Calcium protects <Emphasis Type="Italic">Trifolium repens</Emphasis> L. seedlings against cadmium stress

The effect of calcium (Ca²⁺) on Trifolium repens L. seedlings subjected to cadmium (Cd²⁺) stress was studied by investigating plant growth and changes in activity of antioxidative enzymes. Physiological analysis was carried out on seedlings cultured for 2 weeks on half-strength Hoagland medium with Cd²⁺ concentrations of 0, 400 and 600 μM, and on corresponding medium supplied with CaCl₂ (5 mM). Exposure to increasing Cd²⁺ reduced the fresh weight of the upper part (stems + leaves) of the seedlings more strongly than that of the root system. In both parts of T. repens seedlings H₂O₂ level and lipid peroxidation increased. In the upper part, Cd²⁺ exposure led to a significant decrease in the activity of superoxide dismutase, catalase and glutathione peroxidase and an increase in ascorbate peroxidase activity. In contrast, the roots showed an increase in the activity of antioxidative enzymes under Cd²⁺ stress. Ca²⁺ addition to medium reduced the Cd²⁺ accumulation, and considerably reversed the Cd²⁺-induced decrease in fresh mass as well as the changes in lipid peroxidation in the both parts of T. repens seedlings. Ca²⁺ application diminished the Cd²⁺ effect on the activity of antioxidative enzymes in the upper part, even though it did not significantly affect these enzymes in the roots. So the possible mechanisms for the action of Ca²⁺ in Cd²⁺ stress were considered to reduce Cd²⁺ accumulation, alleviate lipid peroxidation and promote activity of antioxidative enzymes.     

Cadmium accumulation and oxidative burst in garlic (Allium sativum)

To investigate the temporal sequence of physiological reactions of garlic (Allium sativum) to cadmium (Cd) treatment, seedlings developed from cloves were grown in increasing concentrations of CdCl2, ranging from 1-10 mM, for up to 8 days in sand. Analysis of Cd uptake indicated that most Cd accumulated in roots, but some was also translocated and accumulated in leaves at longer exposure time (after 12h) and higher concentrations (5 and 10mM) of CdCl2. Changes in activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were characterized in leaves of garlic seedlings. Cd (5 and 10 mM) initially inhibited the activities of SOD and CAT but thereafter recovered or even increased compared with control plants. POD activities at 5 and 10 mM of Cd increased more than 3-4 times over control plants within 12 h and then dropped, but were still higher than controls at the end of the experiment. Otherwise lipid peroxidation enhanced with the increasing of incubation time and concentrations of external Cd. Leaves exposed to 1 mM CdCl2 showed a less pronounced response and only a small reduction in shoot growth. These results suggested that in leaves of garlic seedlings challenged by CdCl2 at higher concentrations, induction of these various enzymes is part of a general defense strategy to cope with overproduction of reactive oxygen. The possible mechanism of antioxidative enzymes changing before Cd accumulation in leaves of garlic seedlings is discussed.     

Cadmium-induced changes in antioxidant enzyme activities in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. cv. Dongjin)

We studied how the relationship between cadmium (Cd) toxicity and oxidative stress influenced the growth, photosynthetic efficiency, lipid peroxidation, and activity of ntioxidative enzymes in the roots and leaves of rice(Oryza sativa L Dongjin). Plants were exposed to Cd for 21 d. Both seedling growth and photosynthetic efficiency decreased gradually with increasing cadmium concentrations. Lipid peroxidation increased slowly in both roots and leaves, causing oxidative stress. However, each tissue type responded differently to Cd concentrations with regard to the induction/ inhibition of antioxidative enzymes. The activity of Superoxide dismutase (SOD) increased in both roots and leaves. Ascorbate peroxidase (APX) activity increased in leaves treated with up to 0.25 μM Cd, then decreased gradually at higher concentrations. In contrast, APX activity in roots increased and remained constant between 0.25 and 25 μM Cd. Enhanced peroxidase (POD) activity was recorded for treatments with up to 25/M Cd, gradually decreasing at higher concentrations in the leaves but remaining unchanged in the roots. Catalase (CAT) activity increased in the roots, but decreased in the leaves, whereas the activity of glutathione reductase (GR) was enhanced in both roots and leaves, where it remained elevated at higher Cd concentrations. These results suggest that rice seedlings tend to cope with free radicals generated by Cd through coordinated, enhanced activities of the antioxidative enzymes involved in detoxification.     

Effects of exogenous nitric oxide on cadmium toxicity, element contents and antioxidative system in perennial ryegrass

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in ryegrass seedlings (Lolium perenne L.) were studied by investigating the symptoms, plant growth, chlorophyll content, lipid peroxidation, H⁺-ATPase enzyme and antioxidative enzymes. Addition of 100???M CdCl₂ caused serious chlorosis and inhibited the growth of ryegrass seedlings, and dramatically increased accumulation of Cd in both shoots and roots, furthermore, the absorption of macro and micronutrients were inhibited. Addition of 50, 100, 200???M SNP significantly decreased the transport of Cd from roots to shoots, alleviated the inhibition of K, Ca, Mg and Fe, Cu, Zn absorption induced by Cd, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in ryegrass seedlings exposed to Cd, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances. Addition of 50, 100, 200???M SNP significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes also showed the same changes. Addition of 50, 100, 200???M SNP increased activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in ryegrass seedlings exposed to Cd. Addition of 100???M SNP had the most significant alleviating effect against Cd toxicity while the addition of 400???M SNP had no significant effect with Cd treatment.     

Exogenous Application of Selenium Mitigates Cadmium Toxicity in <Emphasis Type="Italic">Brassica juncea</Emphasis> L. (Czern &amp; Cross) by Up-Regulating Antioxidative System and Secondary Metabolites

The main aim of the present study was to examine the role of selenium (Se) in ameliorating the toxic effect of cadmium (Cd) in mustard (Brassica juncea) plants. The plants exposed to elevated levels of Cd exhibited reduced biomass, pigment content, and relative water content (RWC). However, supplementation of Se restores the negative effect of Cd and increases biomass, pigment content, and RWC. Osmolyte (proline and glycine betaine) and sugar content were increased under Cd stress and further increase was observed with addition of Se. Cd decreased protein content and supplementation of Se increases it to appreciable levels. Cd also increased production of H₂O₂ and lipid peroxidation, electrolyte leakage, and the activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and glutathione reductase. Supplementation of Se decreased accumulation of H₂O₂ and lipid peroxidation, increased the activities of antioxidant enzymes to greater levels, and regulates Cd accumulation in roots and shoots. Ascorbic acid (AsA) and flavonoids decreased with elevated concentrations of Cd; however, tocopherol and total phenols were increased with the same concentrations of Cd. Se application maintains AsA and flavonoid content, and further increase in tocopherol and total phenols were observed with Se in the present study. Overall the results confirm that exogenous application of Se mitigates the negative effects of Cd stress in mustard plants through the regulation of osmoprotectants, antioxidant enzymes, and secondary metabolites.     

Antioxidative response to cadmium in roots and leaves of tomato plants

Treatment of tomato seedlings (Lycopersicon esculentum Mill. cv. 63/5 F1) with increasing CdCl₂ concentrations in the culture medium resulted in Cd accumulation more important in roots than in leaves. Biomass production was severely inhibited, even at low Cd concentration. Cd reduced chlorophyll content in leaves and enhanced lipid peroxidation. An increase in antioxidative enzyme (superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase) activities was more pronounced in leaves than in roots, while catalase activity increased only in roots. In addition, changes in isoenzyme composition were observed using the non-denaturing polyacrylamid gel electrophoresis.     

Selenium as an anti-oxidant and pro-oxidant in ryegrass

Selenium is an essential element for antioxidation reactions in human and animals. In order to study its biological role in higher plants, ryegrass (Lolium perenne) was cultivated in a soil without Se or amended with increasing dosages of H₂SeO₄ (0.1, 1.0, 10.0 and 30.0 mg Se kg⁻¹). Ryegrass was harvested twice and the yields were analyzed for antioxidative systems and growth parameters. Selenium exerted dual effects: At low concentrations it acted as an antioxidant, inhibiting lipid peroxidation, whereas at higher concentrations, it was a pro-oxidant, enhancing the accumulation of lipid peroxidation products. The antioxidative effect was associated with an increase in glutathione peroxidase (GSH-Px) activity, but not with superoxide dismutase (SOD) and αα-tocopherol, which was the only tocopherol detected. In the second yield, the diminished lipid peroxidation due to a proper Se addition coincided with promoted plant growth. The oxidative stress found at the Se addition level ≥ 10 mg kg⁻¹ resulted in drastic yield losses. This result indicates that the toxicity of Se can be attributed, in addition to metabolic disturbances, to its pro-oxidative effects. Neither the growth-promoting nor the toxic effect of Se could be explained by the changes in the total chlorophyll concentration. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of phytochelatins and modulation of antioxidants in response to cadmium stress in Cuscuta reflexa--an angiospermic parasite

Effect of cadmium on growth, antioxidative enzymes namely catalase, peroxidase, glutathione reductase, level of glutathione and phytochelatin synthesis was investigated in callus and seedlings of Cuscuta reflexa. A time, concentration and tissue dependent response of Cd was observed. Cd inhibited the growth of callus and seedlings by 50% at 300 and 500 micromol/L concentrations, respectively. Shorter exposure of low concentration of Cd led to augmentation of antioxidant activity, both in callus and seedlings, while longer exposure and high concentration of Cd led to a concentration dependent decrease in callus. Analysis of phytochelatin (PC) synthesis in callus and seedlings of C. reflexa revealed both quantitative and qualitative changes. Cd at low concentrations led to synthesis of predominantly PC4, while at higher concentrations, PC3 was the major form being synthesized. Amelioration of antioxidative systems of C. reflexa in response to Cd stress might be playing a protective role, alleviating the damaging effects of ROS, generated during Cd stress. Concomitantly, chelation and sequestering of toxic Cd ions in this parasite was mediated by synthesis of PC. The response to Cd stress shown by this holoparasitic plant was found to be similar to those of non-parasitic plants (hosts).     

Antioxidative and growth-promoting effect of selenium on senescing lettuce

In human and animal cells, Se plays an essential role in antioxidation and exerts an antiaging function but it is toxic at high dietary intake. To increase its intake in forage and foodstuffs, Se fertilization is adopted in some countries where soils are low in bioavailable Se, even though higher plants are regarded not to require Se. To test its ability to counteract senescence-related oxidative stress in higher plants, a pot experiment was carried out with lettuce (Lactuca sativa) cultivated with increasing amounts of H₂SeO₄. The yields harvested 7 or 14 weeks after sowing revealed that a low Se dosage (0.1 mg kg^–1 soil) stimulated the growth of senescing seedlings (dry weight yield by 14%) despite a decreased chlorophyll concentration. The growth-promoting function was related to diminished lipid peroxidation. In young and senescing plants, the antioxidative effect of Se was associated with the increased activity of glutathione peroxidase (GSH-Px). In the senescing plants, the added Se strengthened the antioxidative capacity also by preventing the reduction of tocopherol concentration and by enhancing superoxide dismutase (SOD) activity. When no Se was added, tocopherols and SOD activity diminished during plant senescence. The higher Se dosage (1.0 mg kg^–1 soil) was toxic and reduced the yield of young plants. In the senescing plants, it diminished the dry weight yield but not the fresh weight yield.     

Membrane permeability and micro- and macroelement accumulation in spring wheat cultivars during the short-term effect of salinity- and PEG-induced water stress

The comparative responses of ten spring wheat cultivars to water stress were investigated. Wheat plants were cultured under hydroponics conditions (Hoagland nutrient) to the stage of three-leaf seedlings. Then, the water medium was supplemented with PEG (drought) or NaCl (salinity) to obtain a water status equal to −1.5 MPa. After a 2-day treatment, the changes in the following parameters were determined: fresh and dry weight, macro- and microelement accumulation, membrane injury (electrolyte leakage, lipid peroxidation) and fatty acid content of the phospholipid fraction of plasmalemma (in comparison to plants not stressed, taken as a control). Generally, the plants were more significantly influenced by water stress stimulated by PEG than by NaCl treatment, as compared to the plants cultivated in the control media. The results of the decrease in water content in leaves and electrolyte leakage from cells corresponded well with the intensity of lipid peroxidation (determined by malondialdehyde—MDA-content) and were chosen for the selection of investigated genotypes for tolerance to both stresses. The more tolerant genotypes exhibited the opposite changes in phospholipid fatty acid unsaturation for two applied stresses i.e. NaCl treatment caused a decrease in unsaturation whereas in PEG-treated plants an increase in unsaturation was observed. These changes were reversed for less tolerant plants, i.e. NaCl treatment influenced an increase in fatty acid unsaturation whereas in PEG-treated plants a decrease in unsaturation was measured. The ratio of U/S (unsaturated to saturated fatty acids) correlated with the total amount of accumulated macroelements. The content of Mg, Ca and S in leaves of plants undergoing both stress factors (NaCl and PEG) dropped whereas the K and P content increased in leaves of wheat seedlings cultured on media containing NaCl only. For microelements, a decrease in the accumulation of these nutrients was detected in all investigated seedlings. However, a greater reduction in the level of these elements occurred in seedlings grown on media with PEG in comparison to those grown on NaCl containing media.     

Effect of Selenium Pre-treatment on Antioxidative Enzymes and Lipid Peroxidation in Cd-exposed Suckling Rats

Since there are no data about the protective role of selenium (Se) against cadmium (Cd)-induced oxidative damage in early life, we studied the effect of Se supplementation on antioxidative enzyme activity and lipid peroxidation (through thiobarbituric acid reactive substances; TBARS) in suckling Wistar rats exposed to Cd. Treated animals received either Se alone for 9 days (8 μmol, i.e., 0.6 mg Se as Na₂SeO₃ kg⁻¹ b.w., daily, orally; Se group), Cd alone for 5 days (8 μmol, i.e., 0.9 mg Cd as CdCl₂ kg⁻¹ b.w., daily, orally; Cd group), or pre-treatment with Se for 4 days and then co-treatment with Cd for the following 5 days (Se + Cd group). Our results showed that selenium supplementation, with and without Cd, increased SOD activity in the brain and kidney, but not in the liver and GSH-Px activity across all tissues compared to control rats receiving distilled water. Relative to the Cd group, Se + Cd group had higher kidney and brain SOD and GSH-Px activity (but not the liver), while in the liver caused increased and in the brain decreased TBARS level. These results suggest that Se stimulates antioxidative enzymes in immature kidney and brain of Cd-exposed rats and could protect against oxidative damage.     

Anti- and pro-oxidative effects of flavonoids on metal-induced lipid hydroperoxide-dependent lipid peroxidation in cultured hepatocytes loaded with α-linolenic acid

Lipid hydroperoxide (LOOH)–dependent lipid peroxidation was induced in α-linolenic acid (LNA)-loaded hepatocytes by adding Fe, Cu, V, or Cd ions at concentrations from 20 to 500 μM. The effects of structurally related flavonoids at concentrations from 10 to 500 μM on the lipid peroxidation were examined. The results with regard to each flavonoid subclass are as follows: (i) Flavonols such as myricetin, quercetin, fisetin, and kaempferol, but not morin, showed dose-dependent antioxidative activity against metal-induced lipid peroxidation at all metal concentrations. Myricetin, quercetin, and fisetin were the most effective antioxidants, although their efficacies depended on the metal ion. Kaempferol and morin had antioxidative activity equal to the other flavonols in the presence of Cu ions, but were much less effective for the other three metal ions. (ii) Flavones, luteolin, apigenin, and chrysin were antioxidative at low Fe concentrations, but were pro-oxidative at high Fe concentrations. Luteolin exhibited antioxidative activity similar to that of catechol-containing flavonols in the presence of the other three metal ions. Apigenin and chrysin also acted as pro-oxidants with V or with all metal ions, respectively. (iii) Taxifolin, a flavanone, also showed both anti- and prooxidative activity, depending on Fe concentrations, but with other metal showed only antioxidative activity ions. (iv) Epigallocatechin, a flavanol, was antioxidative with all metal ions, and its activity was similar to that of catechol-containing flavonols. The various effects of flavonoids on metal-induced lipid peroxidation in LNA-loaded hepatocytes is discussed with regard to the change in redox potential of flavonoid–metal complexes.     

Changes in wheat plastid membrane properties induced by cadmium and selenium in presence/absence of 2,4-dichlorophenoxyacetic acid

The aim of the work was to recognize the effect of cadmium (Cd) and selenium (Se) onto properties of plastid lipid membranes. Plastids were isolated from wheat calli cultured during 2 weeks on Murashige–Skoog media with presence/absence of 2,4-dichlorophenoxyacetic acid. Plastids obtained in presence of 2,4-D represented an earlier developmental stage in comparison to those, got in absence of 2,4-D, which reached a pre-chloroplast stage. The studied metals were introduced to culture media separately (2 μM Na₂SeO₄ or 800 μM CdCl₂) or together (Se + Cd). The changes of following properties of plastid envelope membrane caused by both metals were measured: composition of main lipid fractions, their fatty acid saturation, membrane fluidity, lipid peroxidation and membrane zeta potential. Results of experiments led to the conclusion that galactolipid component plays a predominant role in modification of plastid membrane properties responding to Cd and Se addition. It was shown that galactolipid protecting reaction to Cd toxic action can consists in increased plastid envelope membrane stiffness. The presence of hormone (2,4-D) and Se did not counterbalance Cd toxic effects (at least under concentration level applied in the experiments). Se applied separately can probably stimulate plastid/chloroplast transformation in wheat cells by increasing a galactolipid unsaturation degree. The zeta potentials seem to be important physicochemical parameter in determination of properties of membranes exposed to metal stress conditions.     

亚硒酸盐对油菜幼苗硒吸收、根系形态及生理指标的影响

以甘蓝型油菜(湘农油571)为试验材料,通过溶液培养研究了外源四价硒条件下,油菜幼苗硒吸收分配、生理特性及根系形态的变化.结果表明： 油菜幼苗的硒富集能力随施硒量增加显著降低,而硒分配系数一直稳定在0.9左右,不受硒浓度影响.10 μmol·L^-1硒可以通过显著改善油菜幼苗根系生理指标和根系形态来促进油菜幼苗的生长,其对生理指标的影响主要表现为：显著降低油菜幼苗根系超氧阴离子自由基(O₂^-_·)产生速率,并显著提高超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,从而显著降低根系的膜脂过氧化物质(MDA)含量,降幅达26.0%,进〖JP2〗而显著提高根系活力,增幅达17.4%;其对构型指标促进程度依次为：根体积>总表面积>分根数>总根长>根尖数>平均直径,但这些正效应均与1 μmol·L^-1硒处理无显著差异,表明少量硒(≤10 μmol·L^-1)可以通过提高油菜幼苗根系抗氧化酶活性和降低膜脂过氧化物含量,来提高根系活力和改善根系构型,最终促进油菜幼苗生长.     

Selenium-induced protection of photosynthesis activity in rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) seedlings subjected to cadmium stress. Fluorescence and EPR measurements

Fluorescence and electron paramagnetic resonance measurements were used to study selenium influence on photosystem activity in rape seedlings affected by Cd stress. Water cultures containing Hoagland nutrients were supplemented with 400 μM of CdCl₂, 2 μM of Na₂SeO₄ and a mixture of both CdCl₂ and Na₂SeO₄. The seedlings were cultured till the first leaf reached about 1 cm in length. Cadmium-induced changes in the activity of both photosystems were partly diminished by Se presence in the nutrient medium. Electron microscopy photographs confirmed less degradation in chloroplasts of plants cultured on media containing Se. It is suggested that sucrose groups of starch, which is deposited in greater amounts in Cd-stressed plants, may act as traps for free radicals produced under those conditions.     

Ultrastructure and lipid alterations induced by cadmium in tomato (Lycopersicon esculentum) chloroplast membranes

The effects of cadmium (Cd) uptake on ultrastructure and lipid composition of chloroplasts were investigated in 28-day-old tomato plants (Lycopersicon esculentum var. Ibiza F1) grown for 10 days in the presence of various concentrations of CdCl2. Different growth parameters, lipid and fatty acid composition, lipid peroxidation, and lipoxygenase activity were measured in the leaves in order to assess the involvement of this metal in the generation of oxidative stress. We first observed that the accumulation of Cd increased with external metal concentration, and was considerably higher in roots than in leaves. Cadmium induced a significant inhibition of growth in both plant organs, as well as a reduction in the chlorophyll and carotenoid contents in the leaves. Ultrastructural investigations revealed that cadmium induced disorganization in leaf structure, essentially marked by a lowered mesophyll cell size, reduced intercellular spaces, as well as severe alterations in chloroplast fine structure, which exhibits disturbed shape and dilation of thylakoid membranes. High cadmium concentrations also affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the fatty acid content and a shift in the composition of fatty acids, resulting in a lower degree of fatty acid unsaturation in chloroplast membranes. The level of lipid peroxides and the activity of lipoxygenase were also significantly enhanced at high Cd concentrations. These biochemical and ultrastructural changes suggest that cadmium, through its effects on membrane structure and composition, induces premature senescence of leaves.     

Root phospholipids in Azospirillum-inoculated wheat seedlings exposed to water stress

Azospirillum-plant association is accompanied by biochemical changes in roots which, in turn, promote plant-growth and tolerance to water stress. To shed light on the possible factors underlying these effects, roots from Azospirillum brasilense Sp245-inoculated Triticum aestivum seedlings growing in darkness under osmotic stress were analyzed for phospholipid (PL) composition, fatty acid (FA) distribution profiles and degree of unsaturation of the major PL classes. Azospirillum inoculation diminished ion leakage and increased 2,3,5-tripheniltetrazolium reducing ability in roots of well irrigated and water-stressed wheat seedlings. Total root PL content remained unaltered in all treatments. Six PL classes were detected, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) comprising over 80% of the total. While water stress increased PC content and diminished that of PE, none of these changes were observed either under Azospirillum inoculation alone or when both treatments were combined. The major FAs found in both PC and PE were 16:0, 18:0, 18:1, 18:2, and 18:3. Higher PC and lower PE unsaturation than in well irrigated controls were observed in roots from Azospirillum-inoculated, water-stressed seedlings. Azospirillum inoculation could contribute to protect wheat seedlings from water stress through changes in the FA distribution profiles of PC and PE major root phospholipids.     

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20 μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20 μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.     

CO2激光预处理对PEG6000胁迫下小麦幼苗根中抗氧化酶活性的影响

用CO2激光对小麦种子分别辐照0、1、3、5min,待其生长至12d时,用10%（W/V）PEG6000胁迫其幼苗,研究激光预处理对PEG6000水分胁迫下小麦幼苗根部脂质过氧化伤害的防护作用。结果表明,CO2激光预处理3min可使水分胁迫的小麦幼苗根部MDA、H2O2含量和O2.-产生速率显著降低（P〈0.05）,可显著提高（P〈0.05）小麦幼苗根部SOD、POD、CAT、APX活性和根长、根干重。激光预处理3min可抑制由水分胁迫引起的小麦幼苗根部脂质过氧化作用。