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.     

Comparative assessment of selenite (SeIV) detoxification to elemental selenium (Se0) by <Emphasis Type="Italic">Bacillus</Emphasis> sp.

Bacillus licheniformis, B. subtilis, B. cereus, Bacillus pumilus and Exiguobacterium sp., which were resistant up to 20 mg Na₂SeO₃/ml in nutrient broth and 40 mg/ml on nutrient agar plates, were isolated from contaminated soil and water. They grew from 25 to 45°C and pH 5 to 9. They had multiple metal and antibiotic resistances. All strains reduced selenite (SeIV) to elemental selenium (Se0) aerobically with a maximum reduction of 97% by B. pumilus after 144 h with Na₂SeO₃ at 500 μg/ml.     

In vitro differential effects of sodium selenite on the growth of human hepatoma cells and human embryonic liver cells

The effects of various concentrations of Na₂SeO₃ on human hepatoma cells and human embryonic liver cells was investigated in vitro. For human hepatoma cells, mitotic index and cell count decreased with increasing selenium concentrations. At 1 μg/mL Na₂SeO₃, mitotic activity of human hepatoma cells were partially arrested. In human embryonic liver cells continuously treated with Na₂SeO₃, (1 μg/mL) cell count of the treated group decreased only by d 7; mitotic index, labeled index, and mean silver grain number per 50 labeled nuclei were the same as in the control group on exposure to 1, 3, and 5 μg/mL for up to 72 h. In mixed cultures of human hepatoma and embryonic liver cells treated with 3 and 5 μg/mL of Na₂SeO₃ for 24 h, hepatoma cells showed vacuolated cytoplasms, distorted nuclei, condensed chromatin, and even pyknosis, whereas the embryonic liver cells retained a normal morphology under the same treatment.     

Growth and fruitbody formation ofGanoderma lucidum on media supplemented with vanadium, selenium and germanium

Responses of mycelia ofGanoderma lucidum to vanadium, selenium and germanium were examined over a wide range of concentrations (10–1, 120 μg/ml) in pure culture. Se and V were found to be highly toxic, but Ge was not toxic at the levels tested.Ganododerma lucidum cultivated on substrates of sawdust with V (30–80 μg/g) developed mature fruitbodies, but the bioaccumulation of V was quite low (2.5–7 μg/g in pileus, 12.5–21.5 μg/g in stipe and <1 μg/g in basidiospores). Se as Na₂SeO₄ labeled with⁷⁵Se was effectively taken up from substrates and accumulated in fruitbodies (mainly in pileus), then depleted by discharge of basidiospores. Ge as GeCl₄ labeled with⁷⁷Ge was easily uptaken and translocated into fruitbodies.     

Effect of selenium compounds on the damage induced by oxysterol on rat arterial walls

Wistar rats were fed Se-deficient (0.017±0.002 mg Se/kg) and Seadequate (0.32±0.045 Se mg/kg) diets for 12 mo and then were given 5 mg/kg of cholestane-3β,tα,6β-triol (3-triol), intravenously. Se compounds (Na₂SeO₃ and ebselen) were supplemented in different doses and times to the Se-deficient rats. Twenty-four hours after 3-triol infusion, the changes in ultrastructures of rat aorta were examined by scanning electron micrography (SEM) and transmission electron micrography (TEM). SEM examinations showed that 3-triol induced diffused injuries on arterial endothelial urfaces of long-term Se-deficient rat, and a large number of holes or craterlike defects were observed. TEM examinations further showed that 3-triol induced swelling, necrosis, and shedding of endothelial cells, which resulted in the destruction of endothelial integrity. Mean-while, smooth muscle cells proliferated and migrated toward intimae; the breakage of internal elastic lamina benefited the migration of smooth muscle cells. Supplemented with Na₂SeO₃ (40 μg/kg, 10 d per continuum) and ebselen (20 mg/kg), respectively, exhibited significant protection from damages induced by 3-triol. It seems that protecting mechanisms were different between Na₂SeO₃ and ebselen. The present investigation gave visual evidence that both injuries induced by cholesterol oxides and the Se nutritional status contributed to the development of atherosclerosis.     

Enhancement of the antioxidants ergothioneine and selenium in Pleurotus eryngii var. eryngii basidiomata through cultural practices

Antioxidants are molecules that may reverse, prevent or slow cellular damage caused by free radicals. Increasing dietary intake of antioxidants is thought to reduce oxidative stress that may contribute to the development of several diseases. Mushrooms are known to contain antioxidants such as selenium, ergothioneine and phenolics that may serve this role. Here we sought to enhance selenium and ergothioneine concentration in Pleurotus eryngii var. eryngii basidiomata by modifying the techniques used for their commercial cultivation. To enhance selenium content in mushrooms, substrates were supplemented with sodium selenite (Na₂SeO₃) to reach selenium concentrations of 5 and 10 μg/g. Basidiomata of one commercial isolate (WC888) accumulated selenium up to 4.6 and 9.3 μg/g (d.w.), respectively. Therefore, a serving size (85 g) of fresh P. eryngii mushrooms produced on substrates supplemented with 5 and 10 μg/g of Na₂SeO₃ would supply 70.4 and 116.3% of the daily value of selenium (DV = 70 μg), respectively. Since selenium-enriched mushrooms would supply more than 20% of the DV, they could be considered an excellent source of selenium. Ergothioneine concentration was enhanced in mushrooms produced on low-moisture (55%) substrate compared to the commonly used 60% (high-moisture) in commercial cultivation. Mushrooms produced on low-moisture substrate had ergothioneine concentrations of 3.0 mg/g, while mushrooms produced on high-moisture substrate contained 2.2 mg/g or less. Use of a casing overlay for mushroom production resulted in significant yield increases on low-moisture substrate but not on high-moisture substrate.     

定向驯化对异养蛋白核小球藻硒的耐受性及富集能力的影响

硒(Se)是生物体必不可少的微量元素,硒缺乏会导致人产生克山病、大骨节病等疾病,缺硒也会给畜牧业带来巨大损失。目前的补硒产品存在硒含量和生物利用度低、安全性差等问题,而通过小球藻培养可获得生物利用度高、安全性好的有机硒,因此是非常有应用前景的补硒产品。首先,为了获得对硒的耐受性和富集能力更强的藻种,研究通过定向驯化的方式逐步提高培养基中Na₂SeO₃浓度来驯化蛋白核小球藻,并对驯化时间和驯化过程中Na₂SeO₃的浓度梯度进行了优化。结果表明,驯化后的藻种对硒的耐受性和富集能力明显提高。在5L发酵罐中,驯化后的藻株可以耐受40mg/L的Na₂SeO₃,胞内有机硒合成速率提高了175.6%。之后,在5L发酵罐中进一步优化了硒的补加方式,在异养培养过程中分批补料添加40mg/LNa₂SeO₃时,最终获得的蛋白核小球藻细胞干重达106.4g/L,有机硒含量为1227mg/kg,有机硒合成速率为1.36mg/(L·h)。研究结果与已有蛋白核小球藻异养富硒文献报道的最高细胞密度75g/L和最高有机硒含量560mg/kg相比分别提高了41.9%和119.1%。上述结果表明,通过定向驯化的方法,可大大提高蛋白核小球藻对硒的耐受性和富集能力。     

Accumulation and volatilization of different chemical species of selenium by plants

Selenium (Se) removal from polluted waters and soils is especially complicated and highly expensive. Phytoremediation has been suggested as a low-cost, efficient technology for Se removal. Plants remove Se by uptake and accumulation in their tissues, and by volatilization into the atmosphere as a harmless gas. Unraveling the mechanisms of Se uptake and volatilization in plants may lead to ways of increasing the efficiency of the phytoremediation process. The objectives of this study were: (i) to determine the effect of different Se forms in the root substrate on the capacity of some plant species to take up and volatilize Se; (ii) to determine the chemical species of Se in different plant parts after the plants were supplied with various forms of Se; and (iii) to determine the influence of increasing sulfate levels on plant uptake, translocation, and volatilization of different Se species. Plants of broccoli (Brassica oleracea var. botrytis L.), Indian mustard (Brassica juncea L.), sugarbeet (Beta vulgaris L.) and rice (Oryza sativa L.) were grown hydroponically in growth chambers and treated for 1 week with 20 μM Se as Na₂SeO₄, Na₂SeO₃ or L-selenomethionine (SeMeth) and increasing sulfate levels. The data show that shoots of SeO₄-supplied plants accumulated the greatest amount of Se, followed by those supplied with SeMeth then SeO₃. In roots, the highest Se concentrations were attained when SeMeth was supplied, followed by SeO₃, then SeO₄. The rate of Se volatilization by plants followed the same pattern as that of Se accumulation in roots, but the differences were greater. Speciation analysis (X-ray absorption spectroscopy) showed that most of the Se taken up by SeO₄-supplied plants remained unchanged, whereas plants supplied with SeO₃ or SeMeth contained only SeMeth-like species. Increasing the sulfate level from 0.25 mM to 10 mM inhibited SeO₃ and SeMeth uptake by 33% and 15–25%, respectively, as compared to an inhibition of 90% of SeO₄ uptake. Similar results were observed with regard to sulfate effects on volatilization. We conclude that reduction from SeO₄ to SeO₃ appears to be a rate-limiting step in the production of volatile Se compounds by plants. Inhibitory effects of sulfate on the uptake and volatilization of Se may be reduced substantially if Se is supplied as, or converted to, SeO₃ and/or SeMeth rather than SeO₄. Received: 27 February 1998 / Accepted: 30 March 1998     

Elements of margin of safety,toxicity and action of sodium selenite in a lipopolysaccharide rat model

ProjectBoth septic shock and sodium selenite (Na₂SeO₃) lead to multiple organ failure through oxidation. Na₂SeO₃ has direct oxidant effects above the nutritional level and indirect anti-oxidant properties.In a lipopolysaccharide (LPS) rat model we assessed margin of safety, toxicity and beneficial effect of pentahydrate Na₂SeO₃ (5H₂O·Na₂SeO₃) at oxidant doses.ProcedureIn a three-step study on 204 rats we: (i) observed toxic effects of Na₂SeO₃ injected intraperitoneously (IP) and determined its Minimum Dose Without Toxic effect (MDWT) 0.25–0.35 mg/kg selenium (Se) content; (ii) injected IP LPS at 70% lethal dose (LD) followed, or not, one hour later by IP Na₂SeO₃ at MDWT and (iii) by doses > MDWT. At 48 h, in survivors, we measured plasma creatinine, lactate, aspartate and alanine aminotransferase (AST, ALT), nitric oxide (NO) and Se concentrations.Results(i) Na₂SeO₃ alone did not increase NO and lactate. Encephalopathy appeared at 1 mg Se/kg. Creatinine increased at 1–1.75 mg Se/kg, AST, ALT at 3–4.5 mg Se/kg, and the minimum LD was 3 mg Se/kg. (ii) Mortality after LPS was 37/50 (74%, [62–86%]) vs. 20/30 (67%, [50–84%]) when followed by Na₂SeO₃ at MDWT (p = 0.483) with a decreased in NO (−31%, p = 0.038) a trend for lactate decrease (−19%, p = 0.068) and an increased Se in plasma of survivals. (iii) All rats died at doses ≥0.6 mg/kg (p < 0.001).ConclusionMechanisms of LPS and Na₂SeO₃ toxicity differ (i.e. NO, lactate). In septic shock 5H₂O·Na₂SeO₃ toxicity increased, margin of safety decrease, but IP administration of dose considered as oxidant of 5H₂O·Na₂SeO₃ showed beneficial effects.     

Arsenite-Induced Apoptosis Is Prevented by Selenite in A375 Cell Line

Arsenic trioxide induces apoptosis and clinical remission in patients diagnosed with acute promyelocytic leukemia. The human malignant melanoma A375 cells were treated with NaAsO₂ (0.1–130 μM) and also treated with combined 10 μM NaAsO₂ and 10 μM Na₂SeO₃. NaAsO₂ arrested cell growth in the G1 phase and induced apoptosis in a concentration- and time-dependent manner. In contrast, administration of Na₂SeO₃ antagonized the cell growth inhibition and apoptosis induced by NaAsO₂. The NaAsO₂ treatment resulted in a marked increase in p53 protein as early as 4 h and in Bcl-2 protein level by 12 h. In addition, p53 downregulation accompanied the combined treatment of NaAsO₂ and Na₂SeO₃. Thus, our results indicate upregulation of p53 and Bcl-2 play a crucial role in the NaAsO₂-induced G1 arrest and apoptosis of A375 cells and that downregulation p53 appears to contribute to the inhibition by Na₂SeO₃ of the effects induced by NaAsO₂.     

The effect of dietary selenium supplementation on cadmium absorption and retention in suckling rats

Selenium (Se) reduces cadmium (Cd) toxicity in adult animals, but its effects in newborn animals are still unknown. This study investigated Cd (as CdCl₂) absorption, distribution, and retention in suckling rats receiving oral Se supplementation (as Na₂SeO₃) in equimolar doses (8 μmol Cd and/or Se per kg b.w./day). Selenium was given either before and during Cd exposure (Se_pre + Cd group; pre-treatment group) or only during Cd exposure (Se + Cd group). Rats were treated from postnatal day (PND) 6–14 as follows: controls (H₂O, PND 6–14), Se (PND 10–14), Cd (PND 10–14), Se_pre + Cd (Se PND 6–14 + Cd PND 10–14) and Se + Cd (Se + Cd PND 10–14). Selenium supplementation, especially pre-treatment, decreased Cd levels in the blood, brain, liver and kidney of suckling rats. Selenium levels in plasma, brain, and kidney also decreased. These findings suggest that higher Se intake could efficiently reduce Cd retention during the suckling period.     

In vitro production of radiolabeled red clover (<Emphasis Type="Italic">Trifolium pratense</Emphasis>) isoflavones

Red clover isoflavones are increasingly used in dietary supplements for their purported estrogenic effects. However, little is known about their metabolism in animals due to a lack of commercially available isotopically labeled tracers. The goal of this research was to establish red clover cell culturing methodology for ¹⁴C-biolabeling of isoflavones. When root, leaf, and petiole-derived suspension cultures were grown in darkness or light, dark-grown, petiole-derived solution cultures produced the highest concentrations of the two major red clover isoflavones, formononetin (0.67 mg/g FM inoculum) and biochanin A (0.13 mg/g FM inoculum). Varying levels and timing of copper chloride elicitor did not significantly affect isoflavone accumulation. Approximately 38% of the ¹⁴C-sucrose dose accumulated in the cells. Eighteen percent of the initial labeled dose was detected in the isoflavone-rich methanolic extract and of that, 22% accumulated in isoflavones.     

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.     

Study of the Action of Se and Cu on the Growth Metabolism of <Emphasis Type="Italic">Escherichia coli</Emphasis> by Microcalorimetry

The biological effect of Se and Cu²⁺ on Escherichia coli (E. coli) growth was studied by using a 3114/3236 TAM Air Isothermal Calorimeter, ampoule method, at 37°C. From the thermogenesis curves, the thermokinetic equations were established under different conditions. The kinetics showed that a low concentration of Se (1–10 μg/mL) promoted the growth of E. coli, and a high concentration of Se (>10 μg/mL) inhibited the growth, but the Cu²⁺ was always inhibiting the growth of E. coli. Moreover, there was an antagonistic or positive synergistic effect of Se and Cu²⁺ on E. coli in the different culture medium when Se was 1–10 μg/ml and Cu²⁺ was 1–20 μg/ml. There was a negative synergistic effect of Se and Cu²⁺ on E. coli when Se was higher than 10 μg/ml and Cu²⁺ was higher than 20 μg/ml. The antagonistic or synergistic effect between Se and Cu²⁺ on E. coli was related to the formation of Cu–Se complexes under the different experimental conditions chosen.     

Supplementation with organic or inorganic selenium in heat-distressed quail

The present study was carried out to determine the effects of different sources of selenium (Se; sodium selenite [Na₂SeO₃] or selenomethionine [Se-Met]) supplementation on egg production, egg quality, levels of malondialdehyde (MDA), and Se in serum and egg yolk in heat-stressed Japanese quail (Coturnix coturnix japonica). The birds (n = 360; 55 days old) were randomly assigned to 12 treatment groups consisting of six replicates of five birds each in a 2 × 2 × 3 factorial arrangement of treatments (temperatures, selenium sources, selenium levels). Birds were kept in wire cages in a temperature-controlled room at either 22 (thermoneutral) or 34°C (heat stress) for 8 h/day (09:00–17:00; till the end of study) and fed a basal (control) diet or the basal diet supplemented with either 0.15 or 0.30 mg of Na₂SeO₃ or selenomethionine/kg of diet. Heat exposure decreased live weight, feed intake, feed efficiency, egg production, and egg quality when basal diet was fed (P < 0.0001). A linear increase in feed intake (P = 0.001) and body weight (P = 0.001), egg production (P = 0.001), and improvement in feed efficiency (P = 0.001) and egg quality (P = 0.001) were found in Se-supplemented quail reared under heat stress conditions. Serum, egg white, and egg yolk Se (P ≤ 0.001) concentrations increased linearly, whereas serum, liver, and egg yolk MDA concentrations decreased linearly (P = 0.001) as dietary Na₂SeO₃ or Se-Met supplementation increased. An interaction between dietary Se sources, temperature, and levels of supplementation (P ≤ 0.05) for these parameters was detected. Supplementation with Se improved egg production, egg quality, and antioxidant status of birds, and the effects of Se-Met were relatively greater than Na₂SeO₃ in heat-stressed quail. Results of the present study suggest that supplementation with Se-Met can be considered to be more protective than Na₂SeO₃ by reducing the negative effects of oxidative stress induced by heat stress in quail.     

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.     

Accumulation of isoflavones and pterocarpan phytoalexins in cell suspension cultures of different cultivars of chickpea (Cicer arietinum)

Cell suspension cultures of chickpea (Cicer arietinum L.) were established from cultivars ILC 3279 and ILC 1929, resistant and susceptible towards the chickpea pathogenic fungus Ascochyta rabiei. The two cell culture lines possess identical growth properties and show high accumulation of the isoflavones biochanin A and formononetin together with their glucoside and malonylglucoside conjugates. The cultures of the two cultivars, however, significantly differ in their accumulation of the phytoalexins medicarpin and maackiain essentially as previously demonstrated for the plant genotypes. Phytoalexin formation was elicited by using yeast extract as an inducing agent.     

Effects of Selenium Source and Level on Growth Performance, Tissue Selenium Concentrations, Antioxidation, and Immune Functions of Heat-Stressed Broilers

An experiment is conducted to investigate the effects of selenium (Se) source and level on growth performance, tissue Se concentrations, antioxidation, and immune functions of heat-stressed broilers from 22 to 42?days of age. A total of 210 22-day-old Arbor Acres commercial male chicks were assigned by body weight to one of seven treatments with six replicates of five birds each in a completely randomized design involving a 3?×?2 factorial arrangement plus one Se-unsupplemented basal diet control (containing 0.027?mg of Se/kg). The three Se sources were sodium selenite (Na₂SeO₃), Se yeast, and AMMS Se (Se protein), and the two supplemental Se levels were 0.15 or 0.30?mg Se/kg. All birds were reared under heat-stressed condition (33?±?1?°C during 0900?C1700?hours and 27?±?1?°C during 1900?C0700?hours with a relative humidity of 60?C80?%). The results showed that heat-stressed chicks fed Se-supplemented diets had higher (P?<?0.10) average daily feed intake, Se concentrations in liver and breast muscle, liver glutathione peroxidase (GSH-Px) activity, serum antibody titers against H5N1(Re-4 strain), H5N1(Re-5 strain) and lower (P?<?0.01) mortality compared with the control. Chicks fed the diets supplemented with 0.30?mg/kg of Se had higher (P?<?0.05) Se concentrations in liver and breast muscle, liver GSH-Px activity, and serum antibody titer against H5N1 (Re-4 strain) than those fed the diets supplemented with 0.15?mg/kg of Se. Broilers fed the diets supplemented with Se yeast had higher (P?<?0.001) Se concentrations in liver and breast muscle than those fed the diets supplemented with Na₂SeO₃ or AMMS Se. However, broilers fed the diets supplemented with AMMS Se had higher (P?<?0.05) serum antibody titers against H5N1 (Re-4 strain) and H5N1 (Re-5 strain) than those fed the diets supplemented with Na₂SeO₃. These results indicated that Se yeast was more effective than Na₂SeO₃ or AMMS Se in increasing tissue Se retention; however, AMMS Se was more effective than Na₂SeO₃ or Se yeast in improving immune functions of heat-stressed broilers.     

The antimutagenic effect of selenium on 7,12-dimethylbenz(a)anthracene and metabolites in the amesSalmonella/microsome system

The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene, and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na₂SeO₃ reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion. Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na₂SeO₄ inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that form and concentration are important factors in this trace element's efficacy.     

Effects of ethylene on somatic embryogenesis and galanthamine content in <Emphasis Type="Italic">Leucojum aestivum</Emphasis> L. cultures

The influence of ethylene on in vitro morphogenesis of Leucojum aestivum and galanthamine accumulation was studied. Calli were cultivated on Murashige and Skoog (MS) medium supplemented with 25 μM 4-amino-3,5,6-trichloropicolinic acid (picloram) and 0.5 μM benzyladenine (BA). During incubation under these conditions, callus cultures produced ethylene (9.5 nL/g fresh weight: F.W.) whereas no ethylene was found in somatic embryos cultivated on medium supplemented with 0.5 μM α-naphthalene acetic acid (NAA) and 5 μM zeatin. Application of the precursor of ethylene 1-aminocyclopropane-1-carboxylic acid (ACC) increased ethylene production in both cultures, and decreased callus growth by a factor of 1.2, whereas callus growth was enhanced by a factor of 1.1 in the presence of an inhibitor of ethylene silver nitrate (AgNO₃) or by a factor of 1.2 with an absorbent potassium permanganate (KMnO₄). ACC enhanced the induction of somatic embryos and the development of globular embryos. Removal of ethylene by KMnO₄ during somatic embryogenesis led to the development of plants with greater length. Silver thiosulphate (STS) induced galanthamine production in callus cultures (0.1% dry weight), whereas ACC induced galanthamine production in somatic embryo cultures (2% dry weight).