Zinc phytotoxicity to oilseed rape grown on zinc-loaded substrates consisting of Fe oxide-coated and calcite sand

The risk of zinc (Zn) phytotoxicity in soils has increased in various regions following application of different anthropogenic materials. In order to assess the relative efficiency of Fe oxide and calcite in sorbing Zn and hence alleviating Zn phytotoxicity, we grew oilseed rape for 28 days in pots containing Zn-loaded model substrates consisting of Fe oxide (ferrihydrite)-coated sand (FOCS, 0.2–0.5 mm, 0.3 m² ferrihydrite g^–1 sand) and calcium carbonate (calcite) sand (CCS, 0.2–0.5 mm, 0.3 m² calcite g^–1 sand). Five substrates containing 5, 10, 20, 40, and 80% FOCS and supplied with ZnSO₄ at a rate of 30, 100, 300, and 1000 mg Zn kg^–1 were used in the cropping experiment and in an in vitro study of Zn desorption for 62 days. Plants exhibited good growth and a similar dry matter yield (DMY) at the 30 and 100 mg Zn kg^–1 rates. On the other hand, DMY was markedly reduced at the 300 and, especially, at the 1000 mg Zn kg^–1 rate, particularly for the substrates with the higher FOCS proportions. Symptoms of phytotoxicity (viz. chlorosis, purple colouration due to P deficiency) were apparent at such rates and were accompanied by high Zn concentrations in both shoot (average values >1000 and >1500 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively) and root (average values >2500 and >6000 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively). Total Zn uptake was maximal at 300 mg Zn kg^–1. The results of water extractable Zn in the substrate after cropping and the dissolved Zn concentrations measured in substrate–water systems (desorption experiment) suggest that, on a surface area basis, calcite is more effective than Fe oxide to retain Zn and thus alleviate phytotoxicity at high Zn loadings. However, the Zn-sorption capacity of the Fe oxide cannot be neglected, particularly at low Zn loadings, where Fe oxide seems to exhibit a higher affinity for Zn – but not a higher Zn-sorption capacity – than does calcite.     

Cd Hyperaccumulative Characteristics of Australia Ecotype Solanum Nigrum L. and Its Implication in Screening Hyperaccumulator

A pot culture experiment was used to determine the differences in uptake characteristics of a cadmium hyperaccumulator Solanum nigrum L. discovered in China, an ecotype from Melbourne, Australia and a non-hyperaccumulator Solanum melogena. Australian ecotype was not significantly different to the China ecotype. In particular, Cd concentration in leaves and shoots of S. nigrum collected from Australia were 166.0 and 146.3 mg kg^?1 respectively when 20 mg kg^?1 Cd spiked, and were not significantly different to the ecotype imported from China which had 109.8 and 85.3 mg kg^?1 respectively, in the stems and leaves. In contrast, the tolerance of the eggplant to Cd was significantly less than the two S. nigrum ecotypes. Although some morphological properties of S. nigrum collected from Australia were different from that of the plants collected from China, Cd hyperaccumulator characteristics of two ecotypes were similar. The results suggested that the tolerance and uptake of Cd may be a constitutive trait of this species.     

Change in water quality during the passage through a tropical montane rain forest in Ecuador

We studied five 20-m transects onthe lower slope under tropical lower montanerain forest at 1900–2200 m above sea level. We collectedsamples of soil and of weekly rainfall,throughfall, litter leachate, and stream waterbetween 14 March 1998 and 30 April 1999 anddetermined the concentrations of Al, totalorganic C (TOC), Ca, Cl^–, Cu, K, Mg, Mn,NH₄ ⁺-N, NO₃ ^–-N, total N (TN), Na, P, S, and Zn. The soils were shallowInceptisols; pH ranged 4.4–6.3 in the Ohorizons and 3.9–5.3 in the A horizons, totalCa (6.3–19.3 mg kg^–1) and Mgconcentrations (1.4–5.4) in the O horizon weresignificantly different between the transects.Annual rainfall was 2193 mm; throughfall variedbetween 43 and 91% of rainfall, cloud waterinputs were 3.3 mm a^–1 except forone transect (203). The volume-weighted mean pHwas 5.3 in rainfall and 6.1–6.7 in throughfall.The median of the pH of litter leachate andstream water was 4.8–6.8 and 6.8, respectively.The concentrations of Ca and Mg in litterleachate and throughfall correlatedsignificantly with those in the soil (r =0.76–0.95). Element concentrations inthroughfall were larger than in rainfallbecause of leaching from the leaves (Al, TOC,Ca, K, Mg), particulate dry deposition (TOC,Cu, Cl^–, NH₄ ⁺-N), and gaseousdry deposition (NO₃ ^–-N, total N, S).Net throughfall (= throughfall-rainfalldeposition) was positive for most elementsexcept for Mn, Na, and Zn. High-flow eventswere associated with elevated Al, TOC, Cu, Mn,and Zn concentrations.     

Photosynthetic performance of transplanted ecotypes ofEcklonia cava(Laminariales, Phaeophyta)

Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m^–2s^–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P _max) at 10–29 °C and the light-saturation index (I _k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P _maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m^–2s^–1. However, at lower light intensities of 12.5–50 mol photon m^–2s^–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation.     

Somatic embryogenesis in loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis>) and Douglas fir (<Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis>): improving culture initiation and growth with MES pH buffer,biotin, and folic acid

Loblolly pine (Pinus taeda L.) somatic embryogenesis initiation was improved by supplementing the initiation medium with the pH buffer agent 2(n-morpholino)ethanesulphonic acid (MES) at 250 mg l^–1, folic acid at 0.5 mg l¹, and biotin at 0.05 mg l^–1. MES and vitamins increased the percentage of explants with extruded tissue that continued the initiation process to form embryogenic tissue. The increase in initiation was about 12%. Initiation of 12 open-pollinated families averaged 38.5%, which is 16% higher than initiation on medium without these additives. When tested with 18 control-pollinated families, initiation averaged 26.3%. Basal medium contained a combination of modified 1/2 P6 salts, activated carbon (AC) at 50 mg ^–1, Cu and Zn adjusted to compensate for adsorption by AC, 1.5% maltose, 2% myo-inositol, 500 mg l^–1 casamino acids, 450 mg l^–1 glutamine, 2 mg l^–1 NAA, 0.63 mg l^–1 BAP, 0.61 mg l^–1 kinetin, 3.4 mg l^–1 silver nitrate, 10 M 8-Br-cGMP, 0.1 M brassinolide, and 2 g l^–1 Gelrite. Early-stage embryo growth and initiation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were also improved in the presence of these additives.     

Ecotypes of Holcus lanatus Tolerant to Zinc Toxicity also Tolerate Zinc Deficiency

Genotypes tolerant to zinc (Zn) toxicity, if they accumulateZn in their roots, may grow better than Zn-sensitive genotypes,even in Zn-deficient soil. In the present study, Holcus lanatusL. ecotypes differing in tolerance to Zn toxicity were grownin Zn-deficient Laffer soil which was amended with Zn to createa range of conditions from Zn deficiency to Zn toxicity. IncreasingZn additions to the soil, up to the sufficiency level, improvedgrowth of all ecotypes. At toxic levels of added Zn, the Zn-sensitiveecotype suffered a greater decrease in growth than the Zn-tolerantecotypes. All ecotypes accumulated more Zn in roots than inshoots, with root concentrations exceeding 8 g Zn kg^-1dry weightin extreme cases. When grown in Zn-deficient or Zn-sufficientsoil (up to 0.5 mg Zn kg^-1soil added), ecotypes tolerant toZn toxicity took up more Zn, grew better and had greater rootand shoot Zn concentration than the control (Zn-sensitive ecotype).Zn-tolerant ecotypes transported more Zn, copper (Cu) and iron(Fe) from roots to shoots in comparison with the Zn-sensitiveecotype. The average Zn uptake rate from Zn-deficient soil (noZn added) was greater in the Zn-tolerant ecotypes than in theZn-sensitive ecotype. In conclusion, ecotypes of H. lanatusthat are tolerant to Zn toxicity also tolerate Zn deficiencybetter than the Zn-sensitive ecotype because of their greatercapacity for taking up Zn from Zn-deficient soil. This is thefirst report of the coexistence of traits for tolerance to Zntoxicity and Zn deficiency in a single plant genotype. Copyright2000 Annals of Botany Company Copper, heavy metal, Holcus lanatus, iron, zinc deficiency, zinc toxicity     

Effects of Cd and Zn on the development of annual xylem rings of young Norway spruce (Picea abies) plants

Three-year-old spruce (Picea abies) saplings were planted and cultivated for 2 years in pots with 3 1 substrate, consisting of a homogenized mixture of sand, peat and forest soil with a high organic content (volume ratio 11.52). This substrate was amended with 10–180 mol Cd [kg soil dry weight (DW)]^–1, 50–7500 mol Zn (kg soil DW)^–1 (determined with 1 M ammonium acetate extracts) or combinations of both elements. Annual xylem growth rings in stems of plants treated with 50 mol Cd (kg soil DW)^–1 or 7500 mol Zn (kg soil DW)^–1 were significantly narrower than in control plants. Growth reductions were more pronounced in the second year of the experiment. The contents of Cd and Zn in stem wood and needles were positively correlated with the substrate concentrations. The Mg contents of the spruce needles were inversely correlated with soil concentrations of Cd and Zn. Root development was impeded at moderate concentrations of Cd (50 mol kg^–1) or Zn (1000 mol kg^–1) in the substrate. The adverse effects of potentially toxic trace elements, like Cd or Zn, on xylem growth of spruce plants are discussed with regard to possible growth reductions in forest trees under field conditions.     

Effect of polyethylene glycol and sugar alcohols on soybean somatic embryo germination and conversion

The effect of different vitamins and inorganic micronutrients on callus growth and the induction and proliferation of somatic embryos from young mature, fully expanded leaves of chilli pepper (Capsicum annuum L.) was investigated. Explants were cultured on a solid Murashige and Skoog (MS) medium supplemented with 8% (w/v) sucrose, 12.9 M 6-benzyladenine, 9 M 2,4-dichlorophenoxyacetic acid and 0.5 mg l^–1 thiamin.HCl in various combinations of eleven different vitamins. Alternatively, explants were cultured onto a solid medium containing MS macro- and micronutrients except for the salts of Mn, Zn, I, Cu and Co which were added at either the standard MS concentration or at a tenfold increased (Cu, Co) or decreased (Mn, Zn, I) concentration. The results indicated that somatic embryogenesis from pepper leaves is favoured by the addition of nicotinic acid to the culture medium and the increase of copper concentration (an average induction of 70.2 globular embryos/mm² of explant surface, 9.2% higher than control), without reducing embryo maturation and germination.     

Zinc compartmentation in root, transport into xylem, and absorption into leaf cells in the hyperaccumulating species of Sedum alfredii Hance

Sedum alfredii Hance can accumulate Zn in shoots over 2%. Leaf and stem Zn concentrations of the hyperaccumulating ecotype (HE) were 24- and 28-fold higher, respectively, than those of the nonhyperaccumulating ecotype (NHE), whereas 1.4-fold more Zn was accumulated in the roots of the NHE. Approximately 2.7-fold more Zn was stored in the root vacuoles of the NHE, and thus became unavailable for loading into the xylem and subsequent translocation to shoot. Long-term efflux of absorbed ⁶⁵Zn indicated that ⁶⁵Zn activity was 6.8-fold higher in shoots but 3.7-fold lower in roots of the HE. At lower Zn levels (10 and 100 μM), there were no significant differences in ⁶⁵Zn uptake by leaf sections and intact leaf protoplasts between the two ecotypes except that 1.5-fold more ⁶⁵Zn was accumulated in leaf sections of the HE than in those of the NHE after exposure to 100 μM for 48 h. At 1,000 μM Zn, however, approximately 2.1-fold more Zn was taken up by the HE leaf sections and 1.5-fold more ⁶⁵Zn taken up by the HE protoplasts as compared to the NHE at exposure times >16 h and >10 min, respectively. Treatments with carbonyl cyanide m-chlorophenylhydrazone (CCCP) or ruptured protoplasts strongly inhibited ⁶⁵Zn uptake into leaf protoplasts for both ecotypes. Citric acid and Val concentrations in leaves and stems significantly increased for the HE, but decreased or had minimal changes for the NHE in response to raised Zn levels. These results indicate that altered Zn transport across tonoplast in the root and stimulated Zn uptake in the leaf cells are the major mechanisms involved in the strong Zn hyperaccumulation observed in S. alfredii H.     

The concentration of cadmium,lead, copper and zinc inChironomus gr.thummi larvae (Diptera,Chironomidae) with deformedversus normal menta

The concentrations of Cd, Pb, Cu and Zn inChironomus gr.thummi were determined for 4th instar larvae from the polluted Dyle River, tributary of the Scheldt River (Belgium). Comparison was made between larvae with deformed and normal menta. Deformed larvae showed higher overall metal concentrations than normal larvae. Especially Pb and Cu had higher concentrations in deformed larvae (16.22 mg kg^–1 dry weight and 39.66 respectively) than in normal larvae (12.80 mg kg^–1 dry weight and 35.70 respectively). No significant differences were found in the concentrations of Cd and Zn (mean [Cd] = 0.81 mg kg^–1 dry weight and mean [Zn] = 313.12 mg kg^–1 dry weight). There was no difference between the two larval groups as far as total length, dry weight and developmental stage of the imaginal discs are concerned.     

Using municipal biosolids in combination with other residuals to restore metal-contaminated mining areas

High metal waste materials from historic mining at the Bunker Hill, Idaho (ID) Superfund site was amended with a range of materials including municipal biosolids, woody debris, wood ash, pulp and paper sludge, and compost. The existing soil or waste material has elevated metal concentrations with total Zn, Pb and Cd ranging from 6000 to 14700, 2100 to 27000 and 9 to 28 mg kg^–1, respectively. Surface application of certain amendments including biosolids mixed with wood ash resulted in significant decreases in subsoil acidity as well as subsoil extractable metals. This mixture was sufficient to restore a plant cover to the contaminated areas. At the Bunker Hill site, a surface application of high N biosolids (44 or 66 tons ha^–1) in combination with wood ash (220 tons ha^–1) with or without log yard debris (20% by volume) or pulp and paper sludge (44 tons ha^–1) was able to restore a vegetative cover to the metal contaminated materials for 2 years following amendment application. Plant biomass in 1999 was 0.01 mg ha^–1 in the control versus a mean of 3.4 tons ha^–1 in the residual amended plots. Metal concentrations of the vegetation indicated that plants were within normal concentrations for the 2 years that data were collected. Surface application of amendments was also able to reduce Ca(NO₃)₂ extractable Zn in the subsoil from about 50 mg kg^–1in the control to less than 4 mg kg^–1in two of the treatments. Use of conventional amendments including lime alone and microbial stimulants were not sufficient to support plant growth. These results indicate that surface application of biosolids in combination with other residuals is sufficient to restore a vegetative cover to high metal mine wastes.     

Uptake of lead,cadmium and zinc by the fairy shrimp,Branchinecta longiantenna (Crustacea: Anostraca)

Individuals of the fairy shrimp, Branchinecta longiantenna, were subjected to 5 concentrations (0.1 to 15 mg l^–1) of Pb in diluted habitat water at 13 °C. Lead concentrations (mg kg^–1 wet weight) in the animals were determined at 2-day intervals by digestion in nitric acid followed by atomic absorption analysis. The shrimp were also subjected to 0.1 mg l^–1 media of Cd and Zn, separately.Uptake rates by the fairy shrimp for the three metal ions at 0.1 mg l^–1 were: 0.111, 0.0885, and 0.0460 mg kg^–1 day^–1 for Zn, Pb, and Cd, respectively. After 2 days in 1.0 mg l^–1 Cd or Zn, the animals expired; but they surviced for 8 days in a 10 mg l^–1 Pb medium and for 2 days in 25 mg l^–1 Pb. Lead uptake demonstrated a linear dependence on the Pb concentration in the media.Shrimp survived at much higher tissue accumulations of Pb compared to Zn and Cd. Estimated lethal doses were 20, 1.2–2.4, and 0.4–1.4 mg kg^–1 wet weight for Pb, Zn, and Cd, respectively. Pb was found to be at much lower concentration than Cd or Zn in the natural pond water but between Cd and Zn levels in the sediment. Thus Cd and Zn probably present a greater threat to B. longiantenna than Pb, although Pb may be in higher concentration in the environment.Contribution 47, Laboratory of Ecology, The Claremont Colleges, Claremont, CA 91711, USA. Send reprint requests to Clyde Eriksen.     

The Effects of Hypoxia on Three Sympatric Shark Species: Physiological and Behavioral Responses

Behavioral and physiological responses to hypoxia were examined in three sympatric species of sharks: bonnethead shark Sphyrna tiburo, blacknose shark, Carcharhinus acronotus, and Florida smoothhound shark, Mustelus norrisi, using closed system respirometry. Sharks were exposed to normoxic and three levels of hypoxic conditions. Under normoxic conditions (5.5–6.4mg l^–1), shark routine swimming speed averaged 25.5 and 31.0cm s^–1 for obligate ram-ventilating S. tiburo and C. acronotus respectively, and 25.0cm s^–1 for buccal-ventilating M. norrisi. Routine oxygen consumption averaged about 234.6 mg O₂kg^–1h^–1 for S. tiburo, 437.2mg O₂kg^–1h^–1 for C. acronotus, and 161.4mg O₂ kg^–1 h^–1 for M. norrisi. For ram-ventilating sharks, mouth gape averaged 1.0cm whereas M. norrisi gillbeats averaged 56.0 beats min^–1. Swimming speeds, mouth gape, and oxygen consumption rate of S. tiburo and C. acronotus increased to a maximum of 37–39cm s^–1, 2.5–3.0cm and 496 and 599mg O₂ kg^–1 h^–1 under hypoxic conditions (2.5–3.4mg l^–1), respectively. M. norrisi decreased swimming speeds to 16cm s^–1 and oxygen consumption rate remained similar. Results support the hypothesis that obligate ram-ventilating sharks respond to hypoxia by increasing swimming speed and mouth gape while buccal-ventilating smoothhound sharks reduce activity.     

Impact of picolinic acid on the chromium accumulation in fodder radish and komatsuna

Effects of picolinic acid (2-pyridinecarboxylic acid) and chromium(III) picolinate was studied on the chromium (Cr) accumulation of fodder radish (Raphanus sativus L. convar. oleiformis Pers., cv. Leveles olajretek) and komatsuna (Brassica campestris L. subsp. napus f. et Thoms. var. komatsuna Makino, cv. Kuromaru ) grown in a pot experiment. Control cultures, grown in an uncontaminated soil (UCS; humous sand with pH_KCl 7.48, sand texture with 12.4% clay+silt content, organic carbon 0.56%, CaCO₃ 2.2%, CEC 6.2 cmol_c kg^–1, Cr 10.6 mg kg^–1), accumulated low amounts of chromium (less than 5.4 g g^–1) in their roots or shoots. When this UCS was artificially contaminated with 100 mg kg^–1 Cr (CrCl₃) later picolinic acid treatment promoted the translocation of chromium into the shoots of both species. In fodder radish shoots Cr concentration reached 30.4 g g^–1 and in komatsuna shoots 44.5 g g^–1. Application of ethylene diamine tetra-acetic acid (EDTA) to this Cr contaminated soil had similar effect to picolinic acid. When the UCS was amended with leather factory sewage sediment (which resulted in 853 mg kg^–1 Cr in soil), Cr mobilization was observed only after repeated soil picolinic acid applications. From a galvanic mud contaminated soil (brown forest soil with pH_KCl 6.77, loamy sand texture with 26.6% clay+silt content, organic carbon 1.23%, CaCO₃ 0.7%, CEC 24.5 cmol_c kg^–1, Cd 5.0 mg kg^–1, Cr 135 mg kg^–1, and Zn 360 mg kg^–1) the rate of Cr mobilization was negligible, only a slight increase was observed in Cr concentration of fodder radish shoots after repeated picolinic acid treatments of soil. Presumably picolinic acid forms a water soluble complex (chromium(III) picolinate) with Cr in the soil, which promotes translocation of this element (and also Cu) into the shoots of plants. The rate of complex formation may be related to the binding forms and/or concentration of Cr in soil and also to soil characteristics (i.e. pH, CEC), since the rate of Cr translocation was the following: artificially contaminated soil > leather factory sewage sediment amended soil > galvanic mud contaminated soil. Four times repeated 10 mg kg^–1 chromium(III) picolinate application to UCS multiplied the transport of chromium to shoots, as compared to single 10 mg kg^–1 CrCl₃ treatment. This also suggests that chromium(III) picolinate is forming in the picolinic acid treated Cr-contaminated soils, and plants more readily accumulates and translocates organically bound Cr than ionic Cr. Picolinic acid promotes Cr translocation in soil-plant system. This could be useful in phytoextraction (phytoremediation) of Cr contaminated soils or in the production of Cr enriched foodstuffs.     

Distribution of zinc-tolerant bacteria in stream sediments

The distribution of zinc-tolerant bacteria in sediments from three stream sites containing high (3125 g g^–1), medium (291 g g^–1), and low (109 g g^–1) concentrations of Zn was determined. Zinc tolerance was estimated by the ability of bacteria to grow on media amended with Zn concentrations ranging from 4 to 512 mg 1^–1. The presence of Zn-tolerant bacteria was correlated with the degree of heavy metal contamination; this correlation was more closely associated with readily extractable heavy metal concentrations than with the more rigorously extracted heavy metals. Low concentrations of Zn in media (4 to 16 mg 1^–1) were stimulatory to growth of bacteria from contaminated sites while concentrations as low as 4 mg 1^–1 were inhibitory to bacteria from the control site.     

Dynamics of zinc uptake and accumulation in the hyperaccumulating and non-hyperaccumulating ecotypes of Sedum alfredii Hance

Sedum alfredii Hance has been identified as a Zn-hyperaccumulating plant species native to China. The characteristics of Zn uptake and accumulation in the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii were investigated under nutrient solution and soil culture conditions. The growth of HE was normal up to 1000 μM Zn in nutrient solution, and 1600 mg Zn kg⁻¹ soil in a Zn-amended soil. Growth of the NHE was inhibited at Zn levels ≥250 μM in nutrient solution. Zinc concentrations in the leaves and stems increased with increasing Zn supply levels, peaking at 500 and 250 μM Zn in nutrient solution for the HE and the NHE, respectively, and then gradually decreased or leveled off with further increase in solution Zn. Minimal increases in root Zn were noted at Zn levels up to 50 μM; root Zn sharply increased at higher Zn supply. The maximum Zn concentration in the shoots of the HE reached 20,000 and 29,000 mg kg⁻¹ in the nutrient solution and soil experiments, respectively, approximately 20 times greater than those of the NHE. Root Zn concentrations were higher in the NHE than in the HE when plants were grown at Zn levels ≥50 μM. The time-course of Zn uptake and accumulation exhibited a hyperbolic saturation curve: a rapid linear increase during the first 6 days in the long-term and 60 min in the short-term studies; followed by a slower increase or leveling off with time. More than 80% of Zn accumulated in the shoots of the HE at half time (day 16) of the long-term uptake in 500 μM Zn, and also at half time (120 min) of the short-term uptake in 10 μM ⁶⁵Zn²⁺. These results indicate that Zn uptake and accumulation in the shoots of S. alfredii exhibited a down-regulation by internal Zn accumulated in roots or leaves under both nutrient solution and soil conditions. An altered Zn transport system and increased metal sequestration capacity in the shoot tissues, especially in the stems, may be the factors that allow increased Zn accumulation in the hyperaccumulating ecotype of S. alfredii. Section Editor: F. J. Zhao     

Bioventing of diesel oil-contaminated soil: Comparison of degradation rates in soil based on actual oil concentration and on respirometric data

The effects of bioventing, nutrient addition and inoculation with an oil-degrading bacterium on biodegradation of diesel oil in unsaturated soil were investigated. A mesocosm system was constructed consisting of six soil compartments each containing 6 m³ of naturally contaminated soil mixed 11 with silica sand, resulting in a diesel oil content of approximately 2000 mg kg^–1. Biodegradation was monitored over 112 days by determining the actual diesel oil content of the soil and by respirometric tests. The best agreement between calculations of degradation rates based upon the two methods was in July, when venting in combination with nutrient addition resulted in degradation rates of 23 mg kg^–1 day^–1 based on actual oil concentration in the soil and 33 mg kg^–1 day^–1 calculated from respirometric data. In September, these rates decreased to 9 and 1.4 mg kg^–1 day^–1, and in October the degradation rates were 5 and 0.7 mg kg^–1 day^–1 based upon the two methods. The average ambient temperature during the respirometric tests was 14,10 and 2°C in July, September and October, respectively. The combination of venting and nutrient addition resulted in an average residual oil content of the soil of 380 mg kg^–1. Neither venting alone nor inoculation enhanced oil degradation. The respiratory quotient averaged 0.40. The oil composition changed following degradation resulting in the unresolved complex mixture constituting up to 96% of the total oil content at the end of the experimental period.     

Concentrations of physiologically important metal ions in glial cells cultured from chick cerebral cortex

Energy dispersive x-ray fluorescence and atomic absorption spectroscopy were used to determine the concentrations of Mg, Ca, Mn, Fe, Zn, and Cu in primary cultures of astroglial cells from chick embryo cortex in chemically defined serum-free growth medium. The intracellular volume of cultured glia was determined to be 8.34 l/mg protein. Intracellular Mn, Fe, Zn, and Cu in these cells were ca. 10–200 M, or 20–200 times the concentrations in the growth medium. Mg²⁺ was 7 mM in glial cells, only four-fold higher than in growth medium. Glutamine synthetase (GS), compartmentalized in glia, catalyzes a key step in the metabolism of neurotransmitterl-glutamate as part of the glutamate/glutamine cycle between neurons and glia. Hormones (insulin, hydrocortisone, and cAMP) added to growth medium differentially altered the activity of GS and the intracellular level of Mn(II), but not Mg(II). These findings suggest the possibility that glutamine synthetase activity could be regulated in brain by the intracellular levels of Mn(II) or the ratio of Mn(II)/Mg(II), which may in turn be controlled indirectly by means of transport processes that respond to hormones or secondary metabolic signals.     

Content,absorption quantities and intracellular storage sites of heavy metals in Diplopoda (Arthropoda)

By means of atomic absorption spectrophotometry, concentrations of more than 2500 mg kg^–1 Pb, 150 mg kg^–1 Zn, and 320 mg kg^–1 Cd could be detected in the intestine tissues of diplopods from a lead and silver smelter's spoil bank. While only small portions of the ingested lead and cadmium are absorbed in the midgut of these diplopods, the zinc uptake into the midgut epithelium reaches 33.8–37.5% of the zinc content in the food pulp when the animals were contaminated acutely. However, after long-term contamination with zinc, absorption and excretion of this metal balanced one another. Absorbed lead and cadmium are predominantly stored in the midgut cells of the diplopods; unspecific precipitation of heavy metal showed the spherites of the resorptive epithelial cells to be the main accumulation sites. Zinc is for the most part localized in or near the cuticle; electron energy loss spectroscopy and ESI electron spectroscopic imaging, however, showed this metal to be present also in the spherites of the midgut's resorption cells. These spherites are assigned to belong to the type A granule group since (i) they are concentrically structured, (ii) they are shown to contain great amounts of calcium and (iii) copper, a class B metal, could not be detected in these deposits.