Do Armeria maritima (Mill.) Willd. ecotypes from metalliferous soils and non-metalliferous soils differ in growth response under Zn stress? A comparison by a new artificial soil method

Morphological and biogeographical evidence suggests that theheavy-metal ecotype of Armeria maritima (Mill.) Willd. has evolvedfrom a hybrid group between the subspecies maritima from saltmarshes and the subspecies elongata from sandy soils. As partof a study on the ecotypic differentiation in A. maritima, Znresistance was compared in populations from these three ecotypes.To study the long-term growth response to elevated Zn concentrations,an artificial soil was made from ion-exchange resin embeddedin an inert sand matrix, in which metal ions were buffered byan ion-exchange system as in natural soils. In contrast to hydroponics,this artificial soil systems is suitable for long-term cultivationand it provides more reproducible growth conditions than a soilsystem. The long-term growth response in the artificial soilsystem was compared to the growth response to elevated Zn concentrationsin a sand nutrient-solution system. In short-term tests, populationsfrom non-metalliferous soils were more sensitive to Zn concentrationsof 1.0 mmol ^–1 than the heavy-metal populations. However,in long-term tests, the growth of adult plants from all populationswas not inhibited by Zn concentrations up to 2.8 mmol kg^–1dry soil (equivalent 26% of cation-exchange capacity). The Znresistance of all populations could therefore be sufficientfor their survival on Zn mine soils. The discrepancy betweenlong-term tests and short-term tests is discussed with respectto the hypothesis that ‘sensitive’ populations maydiffer from ‘resistant’ populations in the expressionof Zn-resistance mechanisms. Key words: Armeria maritima, growth tests, heavymetal resistance, synthetic ionexchange resins, Zn     

不同生态型东南景天对土壤中Cd的生长反应及吸收积累的差异性

 采用盆栽方法研究了两种生态型东南景天(Sedum alfredii)对土壤中不同含量Cd(即对照, 12.5, 25, 50, 100, 200, 300, 400 mg&;#8226;kg^－1)的生 长反应、吸收和积累Cd的差异性。结果表明,土壤添加重金属Cd后,矿山生态型东南景天生长正常,地上部和根系Cd含量随着土壤中Cd含量的 增加而增加,在400 mg&;#8226;kg^－1 Cd处理下含量分别高达2 900和500 mg&;#8226;kg^－1,其地上部显著大于根部;然而,土壤添加Cd后,非矿山生态型东 南景天的生长受到抑制,地上部和根部的生物量显著降低。当土壤Cd含量为50～100 mg&;#8226;kg^－1 时,非矿山生态型东南景天的地上部和根系Cd含 量随着土壤中Cd含量的增加而增加,而且根系Cd含量则大于地上部。当土壤Cd≤50 mg&;#8226;kg^－1时,矿山生态型东南景天根系Cd含量比非矿山生态 型高 ,但当土壤Cd≥100 mg&;#8226;kg^－1,两者之间无显著差异;然而,但在同一Cd处理水平下,矿山生态型东南景天地上部Cd含量总是高于非矿山 生态型。这些结果表明,矿山生态型东南景天有很强的忍耐和吸收土壤Cd的能力,再次证明其为一种Cd超积累植物。     

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     

Detecting shape differences in species of the Littorina saxatilis complex by morphometric analysis

We investigated variation in shell size and shape of marinesnail species of the Littorina saxatilis complex (L. saxatilis,L. compressa and L. arcana) using geometric morphometric methods.These morphologically similar periwinkle species that are commonin the European intertidal have presented many problems fordiagnosis based on morphology alone. A discriminant analysisdemonstrated that geometric morphometrics is very efficientfor diagnosing individuals to species among sympatric populations.We successfully diagnosed an average of 96% of the specimens(with 85.7–100% correct diagnosis for specific comparisons).The diagnosis capability of this method is absolute at the populationlevel. This makes the technique potentially useful for the designof manipulative field or laboratory experiments. Moreover, ageometric-morphometric analysis was also accomplished in twosnail ecotypes (H and M) of L. saxatilis from rocky shores ofNE England which are apparently adapted to different degreesof wave exposure. We found that the H (exposed) ecotype hasa relatively rounded shell shape with a bigger aperture, whereasthe M (protected) ecotype has a smaller aperture. (Received 23 March 2006; accepted 25 January 2007)     

Zinc, Lead and Cadmium Tolerance, Uptake and Accumulation by the Common Reed,Phragmites australis(Cav.) Trin. ex Steudel

Zinc (Zn), lead (Pb) and cadmium (Cd) tolerance in populationsof seedlings ofPhragmites australisraised from seeds collectedfrom a mine site (Plombières, Belgium) contaminated withZn, Pb and Cd and three ‘clean’ sites (Felixstowe,UK; Wisbech, UK; and Mai Po, Hong Kong) were studied under glasshouseconditions. Small differences were found between the metal-contaminatedpopulation and the three ‘clean’ populations whenseedlings were grown in 1.0 µg  ml^-1Zn and 10.0 µgml^-1Pb treatment solutions. In general, however, different populationsof seedlings showed similar growth responses, metal uptake andindices of Zn, Pb and Cd tolerance when cultured in the samemetal-contaminated media for 89 d or in the same metal treatmentsolutions (ZnSO₄:1.0 and 4.0 µg ml^-1Zn; Pb(NO₃)₂: 10.0and 25.0 µg ml^-1Pb; CdSO₄: 0.5 and 1.0 µg ml^-1Cd)for 3 weeks. There was insufficient evidence to support thehypothesis that the metal-contaminated population has evolvedto a Zn-, Pb- or Cd-tolerant ecotype but the results indicatedsome differentiation between the populations with that fromHong Kong being the least productive under the experimentalconditions used. The implications of the findings on selectionof provenances for use in constructed wetlands for wastewatertreatment are discussed. Metal accumulation; heavy metal tolerance; Phragmites australis; population differentiation     

CADMIUM, COPPER AND LEAD IN GASTROPODS OF THE LOWER NELSON RIVER SYSTEM, MANITOBA, CANADA

Cadmium, copper and lead were examined in whole snails fromthe Lower Nelson River system. Concentrations of the three metalswere significantly correlated with each other. Lead was accumulatedleast, while copper was present in the greatest concentrations.Significant interspecific differences were found for copper.Total body burdens increased with snail size and weight, butconcentrations per unit dry weight decreased with size and weightin some species. Metal concentrations in snails were not significantlycorrelated with metal content of the sediments. In Gyraulus,copper and lead concentrations were correlated with levels ofthese metals in the host macrophytes. Seasonal differences inmetal concentration appeared to be related to differences inage structure of the populations. (Received 5 September 1991; accepted 30 October 1991)     

Cyst production in four species of neritic dinoflagellates

The production of resting cysts in four species of dinoflagellates(Scrippsiella trochoidea, Ensiculifera sp., Alexandrium lusitanicumand Lingulodinium polyedra) was studied in response to severalenvironmental factors of ecological importance (nitrate, phosphate,iron, copper and cyanocobalamin deficiencies, high concentrationsof copper, turbulence, darkness plus concentration. as wellas various media biologically conditioned by dinoflagellates)using unialgal cultures and enrichments of natural populations.Some nutritional deficiencies, mainly phosphorus or nitrogen(in this order), are the most effective inducers of encystment.Among the other deficiencies tested, only iron deficiency wasimportant, affecting only A.lusitanicum. In some cases, biologicalconditioning produced considerable encystment reductions, makingit an important means of competition between species. We suggestthat encystment may be induced in these neritic species by deficienciesin compounds that act as indicators of changes in the hydrographicconditions to which the particular species are adapted.     

The Translocation of Lead and Copper in Two Submerged Aquatic Angiosperm Species

The translocation of lead and copper was studied in two speciesof submerged aquatic angiosperm, Potamogeton crispus L. andPotamogeton pectinatus L. A perspex container incorporatinga potters' clay seal around the stems of intact plants was designedfor the chemical separation of the shoot and root environmentsduring 11–21 d treatment periods. Metal solutions wereadded to the root or shoot environments and concentrations weremonitored in waters and sediments. A technique was developedfor the direct quantitative analysis of metals in small (0.02–0.2mg) segments of water plant tissue, using the graphite rod attachmentto an atomic absorption spectrophotometer. Experimental resultsindicated minimal translocation of lead, but extensive acropetaltranslocation of copper to particular sites of accumulation.     

CADMIUM, LEAD AND COPPER IN FRESHWATER MUSSELS FROM THE ASSINIBOINE RIVER, MANITOBA, CANADA

Cadmium, lead and copper levels were examined in adductor muscle,foot, gonad, mantle, gill, and heart of 9 species of freshwatermussels from the Assini-boine River, using anodic strippingvoltametry. Metal levels in most organs were lower than in bottomsediments. The metals generally showed significantly higherconcentrations in heart and hemolymph samples than in the othertissues examined. However in four species, gill tissues showedthe highest values forcopper, and Quadrula quadnda and Ligumiarecta accumulated the greatest amounts of copper overall. Cadmiumconcentrations were particularly high in heart and hemolymphof Lampsilis radiata sili-quoidea, L. vcntricosa, and Ligumiarecta. Metal concentrations in tissues of a given species showedvarious relationships to weight of soft parts, shell length,and shell weight, but inverse correlations predominated, indicatingthat metals in many organs were less concentrated in older individuals.In L. radiatasiliquoidea and L. vcntricosa, copper concentrationswere higher in males than in females. Lead levels were alsohigher in L. vcntricosamales. (Received 24 June 1994; accepted 8 September 1994)     

Energy-dependent redox state of heme a+a3 and copper of cytochrome oxidase in perfused rat brain in situ

Using theblood-free perfused rat brain, we examined the redox behavior ofcytochrome oxidase of two chromophores, hemea + a₃ and copper.When perfusate inflow was stopped to induce global ischemia,the reduction of heme a + a₃ was triphasic,with a rapid phase, a slow phase, and a second rapid phase. Incontrast, the reduction of copper was monophasic after the rapid phaseof heme a + a₃. The triphasicreduction of heme a + a₃ was diminished by energy-depleting treatments, such as addition of an uncoupler. Thetime course of the reduction of copper was not affected by the energydepletion. During global ischemia the decrease in creatine phosphate nearly paralleled the reduction of hemea + a₃, whereas ATPremained at the control level until ~60% of hemea + a₃ was reduced inthe rapid phase. In the slow phase, ATP started to decrease with thereduction of copper. The redox behavior of copper was similar to theslow phase of the reduction of heme a + a₃ because ofthe higher oxygen affinity of copper than of hemea + a₃. Therefore,the rapid phase of the reduction of hemea + a₃ can be used asan alarm before a decrease in ATP, whereas the reduction of copperindicates a decrease in ATP under severe hypoxia. Thus the coppersignal in noninvasive near-infrared spectroscopy is a useful parameterfor the clinical setting.

     

Mismatch in the distribution of floral ecotypes and pollinators: insights into the evolution of sexually deceptive orchids

Plants are predicted to show floral adaptation to geographic variation in the most effective pollinator, potentially leading to reproductive isolation and genetic divergence. Many sexually deceptive orchids attract just a single pollinator species, limiting opportunities to experimentally investigate pollinator switching. Here, we investigate Drakaea concolor, which attracts two pollinator species. Using pollinator choice tests, we detected two morphologically similar ecotypes within D. concolor. The common ecotype only attracted Zaspilothynnus gilesi, whereas the rare ecotype also attracted an undescribed species of Pogonothynnus. The rare ecotype occurred at populations nested within the distribution of the common ecotype, with no evidence of ecotypes occurring sympatrically. Surveying for pollinators at over 100 sites revealed that ecotype identity was not correlated with wasp availability, with most orchid populations only attracting the rare Z. gilesi. Using microsatellite markers, genetic differentiation among populations was very low (G_ST = 0.011) regardless of ecotype, suggestive of frequent gene flow. Taken together, these results may indicate that the ability to attract Pogonothynnus has evolved recently, but this ecotype is yet to spread. The nested distribution of ecotypes, rather than the more typical formation of ecotypes in allopatry, illustrates that in sexually deceptive orchids, pollinator switching could occur throughout a species' range, resulting from multiple potentially suitable but unexploited pollinators occurring in sympatry. This unusual case of sympatric pollinators highlights D. concolor as a promising study system for further understanding the process of pollinator switching from ecological, chemical and genetic perspectives.     

Environmental relevance of heavy metal-substituted chlorophylls using the example of water plants

Following experiments which studied the substitution of thecentral ion of isolated chlorophylls by heavy metal ions invitro, in vivo experiments with submersed water plants werecarried out. It was discovered that the substitution of thecentral atom of chlorophyll, magnesium, by heavy metals (mercury,copper, cadmium, nickel, zinc, lead) in vivo is an importantdamage mechanism in stressed plants. This substitution preventsphotosynthetic light-harvesting in the affected chlorophyllmolecules, resulting in a breakdown of photosynthesis. The reactionvaries with light intensity. In low light irradiance all thecentral atoms of the chlorophylls are accessible to heavy metals,with heavy metal chlorophylls being formed, some of which aremuch more stable towards irradiance than Mg-chlorophyll. Consequently,plants remain green even when they are dead. In high light,however, almost all chlorophyll decays, showing that under suchconditions most of the chlorophylls are inaccessible to heavymetal ions. Key words: Heavy metal chlorophylls, submersed water plants, antenna pigments, copper, zinc     

Population differentiation within Festuca rubra L. with regard to soil salinity and soil water

Summary Seed and transplanted adult plants from populations of Festuca rubra, collected from inland, salt-marsh and sand-dune sites were grown on culture solution with added sodium chloride. The growth of the populations of the three habitats was reduced differentially by salt. The salt marsh ecotype Festuca rubra ssp. litoralis was only slightly affected and the inland ecotype F. rubra ssp. rubra was severely retarded at 60 mM NaCl. The dune ecotype F. rubra ssp. arenaria had an intermediate tolerance. The tolerant ecotypes accumulated less sodium chloride as compared to the sensitive ecotype, suggesting that salt tolerance is caused in part by salt exclusion.In addition, the dune ecotype F.r. arenaria appeared to be more drought tolerant than the salt marsh ecotype. Abscission of salt-saturated leaves does not function as an adaptation to salinity in Festuca rubra.All three ecotypes accumulated proline with increased salinity. The response was most pronounced in the drought tolerant F.r. arenaria, indicating that proline accumulation is a response to osmotic stress rather than to ion-specific effects of salinity. The observed differences in salt tolerance may be explained by differential sensitivity to toxic effects of sodium chloride.The occurrence on a beach plain of closely adjacent populations of F.r. arenaria and F.r. litoralis, differing markedly in salt tolerance, is briefly discussed.     

Accumulation, subcellular localization and ecophysiological responses to copper stress in two Daucus carota L. populations

Copper accumulation, subcellular localization and ecophysiological responses to excess copper were investigated using pot culture experiments with two Daucus carota L. populations, from a copper mine and an uncontaminated field site, respectively. Significant differences of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations and antioxidant enzyme [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)] activities of leaves under Cu treatment were observed between the two populations. At high Cu concentrations (400 and 800 mg kg⁻¹), a significant increase in contents of MDA and H₂O₂ but a significant decrease in activities of SOD, CAT and APX were observed in uncontaminated population. Contrarily, the population from copper mine maintained a lower level of MDA and H₂O₂ but higher activities of SOD, CAT and APX. Copper accumulation in roots and shoots increased significantly with the increase of copper concentrations in soils in the two populations. No significant difference of the total Cu in roots and shoots was found between the two populations at same copper treatment. There were also no striking differences of cell wall-bound Cu and protoplasts Cu of leaves between the two populations. The difference was that Cu concentration in vacuoles of leaves was 1.5-fold higher in contaminated site (CS) population than in uncontaminated site population. Hence, more efficient vacuolar sequestration for Cu and maintaining high activities of SOD, CAT and APX in the CS population played an important role in maintaining high Cu tolerance.     

Enzymes of Heavy-Metal-Resistant and Non-Resistant Populations of Silene cucubalus and Their Interaction with Some Heavy Metals in vitro and in vivo

The in vitro and in vivo effects of copper, zinc, cadmium, nickel, cobalt, and manganese on nitrate reductase, malate dehydro-genase, isocitrate dehydrogenase, and glucose-6-phosphate dehydrogenase of zinc-, copper- and non-resistant populations of Silene cucubalus were investigated. During the in vitro experiments no resistant enzyme could be detected; enzymes of resistant and non-resistant ecotypes had a similar sensibility to all the metals. Nitrate reductase was the most sensitive enzyme. During the in vivo experiments remarkable differences were found. The nitrate reductase and the isocitrate dehydrogenase of the zinc-resistant population were activated when adding zinc to the culture medium, especially the nitrate reductase showed high activities at zinc concentrations where the nitrate reductase of the non-zinc-resistant populations was nearly completely inhibited. The zinc-resistant ecotype had a real need for zinc.     

Plasmolysis effects and osmotic potential of two phylogenetically distinct alpine strains of Klebsormidium (Streptophyta)

The osmotic potential and effects of plasmolysis were investigated in two different Klebsormidium strains from alpine habitats by incubation in 300–2,000 (3,000) mM sorbitol. Several members of this genus were previously found to tolerate desiccation in the vegetative state yet information was lacking on the osmotic potentials of these algae. The strains were morphologically determined as Klebsormidium crenulatum and Klebsormidium nitens. These species belong to distinct clades, as verified by phylogenetic analysis of the rbcL gene. K. crenulatum is part of to the K. crenulatum/mucosum (‘F’ clade) and K. nitens of the ‘E2’ clade. Plasmolysis occurred in K. crenulatum at 800 mM sorbitol (961 mOsmol kg^?1, Ψ?=??2.09 MPa) and in K. nitens at 600 mM sorbitol (720 mOsmol kg^?1, Ψ?=??1.67 MPa). These are extraordinarily high osmotic values (very negative osmotic potentials) compared with values reported for other green algae. In K. crenulatum, the maximum photosynthetic rate (Pmax) in the light-saturated range was 116 μmol O₂ h^?1 mg^?1 chl a. Incubation in 1,000 mM sorbitol decreased Pmax to 74.1% of the initial value, whereas 2,000 mM sorbitol (Ψ?=??5.87 MPa) lead to an almost complete loss of oxygen production. In K. nitens, Pmax was 91 μmol O₂ h^?1 mg^?1 chl a under control conditions and incubation in 800 mM sorbitol did not decrease Pmax, 2,000 mM sorbitol decreased Pmax only to about 62.6% of the initial value whereas 3,000 mM sorbitol stopped oxygen evolution. This indicated a broader amplitude for photosynthesis in the examined strain of K. nitens. Control samples and samples plasmolysed for 3 h in 800 mM sorbitol (K. nitens), 1,000 mM sorbitol (K. crenulatum), or 2,000 mM sorbitol were investigated by transmission electron microscopy after chemical or high-pressure freeze fixation. In cells undergoing plasmolysis the protoplasts were retracted from the cell wall, the cytoplasm appeared dense, vacuoles were small and fragmented, and the cytoplasm was filled with ribosomes. Thin cytoplasmic strands were connected to the cell wall; 2,000 mM sorbitol increased the effect. The content of soluble carbohydrates in these two strains was investigated by HPLC, as this is one known mechanism for cells to maintain high osmotic pressure of the cytosol. Both Klebsormidium species contained diverse soluble carbohydrates, including a dominant mixed peak of unidentified oligosaccharides, and more minor amounts of raffinose, sucrose, glucose, xylose, galactose, mannose, inositol, fructose, glycerol, mannitol, and sorbitol. The total content of soluble carbohydrates was approximately 1.2% of the dry weight, indicating that this is not a major factor contributing to the high osmotic potential in these strains of Klebsormidium.     

The Cessation of Apical Growth in Latitudinal Ecotypes and Ecotype Crosses of Salix pentandra L

Apical growth cessation in seedling progenies of three latitudinalecotypes and ecotype crosses of Salix pentandra L. was investigatedunder controlled growth conditions and out-of-doors. The southernecotype (59° 40' N) was characterized by late growth cessationunder short day conditions, short critical photoperiod for growthcessation, and high light sensitivity; the northern ecotype(69° 39' N) by rapid growth cessation, long critical photoperiod,and low light sensitivity. The geographically intermediate ecotype(64° 28' N) had an intermediate photoperiodic response.The hybrid progenies were, however, closer to the southern thanto the northern parent ecotype indicating a tendency to favourinheritance of southern characters. Fluctuating temperatures(21 °C/9 °C and 18 °C/9 °C) induced growth cessationin the northern ecotype but not in the other ecotypes or ecotypecrosses with the exception of a few plants of the intermediateecotype and of two hybrid progenies. The time course of apicalgrowth cessation in various progenies grown out-of-doors at69° 39' N was similar to that observed under SD conditionsexcept that the differences between the northern ecotype andthe other ecotypes and crosses were greater.     

Growth and mineral element composition in two ecotypes of Thlaspi caerulescens on Cd contaminated soil

The heavy metal hyperaccumulator Thlaspi caerulescens occurs both on heavy metal polluted soils (metallicolous ecotype MET) and on soils with normal heavy metal content (non-metallicolous ecotype: NMET). In order to assess the extent and structure of variation in growth, shoot accumulation of Cd, Zn and mineral element (Ca, Mg, K, Fe), a MET ecotype from Belgium and a NMET ecotype from Luxembourg were studied. Seven maternal families from two populations of each ecotype were grown on both Cd and Zn contaminated soil. Although both ecotypes presented a similar heavy metal tolerance in the experimental conditions tested, they differed in several points. The MET populations had markedly higher biomass and higher root:shoot ratio compared to NMET populations. The Zn, and at lesser extent, the Cd hyperaccumulation capacity tended to be higher in the NMET populations. The same trend was observed for the foliar concentrations of Mg, Ca and Fe with NMET populations having higher concentrations compared to MET ones. Cd and Zn concentrations were negatively correlated with the biomass of both ecotype. However, the negative correlation between the Zn and biomass was much lower in MET ecotype suggesting a tighter control of internal Zn concentration in this ecotype. Finally, although the Cd phytoextraction capacity was similar in both ecotype, a higher Zn phytoextraction capacity was detected in NMET ecotype when these plants grow on moderate Cd and Zn concentrations.     

BARNACLE-DWELLING EGOTYPES OF THREE BRITISH LITTORINA SPECIES AND THE STATUS OF LITTORINA NEGLECTA BEAN

On the basis of collections from SW Wales and W Ireland it isshown that small (<5 mm) black and/or white Littorina occurringin the barnacle zone on exposed shores, of the L. neglecta shelltype, comprise three species. From their reproductive anatomythese correspond to L. saxatilis, L. arcana and L. nigrolineata,and are interpreted as analogous barnacle-dwelling ecotypesof these species. This adds to the evidence that L. neglectais not a distinct species, but an ecotype of L. saxatilis. (Received 1 June 1992; accepted 23 June 1992)     

Variation in Copper Tolerance among Homokaryotic and Dikaryotic Mycelia of Polyporus palustris Berk. et Curt.

Investigations were made of the variation in copper toleranceamong homokaryons and dikaryons originating from one dikaryoticisolate of Polyporus palustris, as shown by their growth onnutrient agar containing copper sulphate, usually at 0.32 Mconcentration (c. 8 per cent of CuSO₄.5H₂O). Homokaryons obtainedby monobasidiospore isolation were crossed and further homokaryonsobtained in the same way. Selection for copper tolerance gavean increase in the second generation, but no further increasein the third; whilst selection for copper sensitivity gave substantialincreases in both second and third generations. It is concludedthat copper tolerance in this fungus is controlled by a numberof genes. It was found that, in this fungus, the copper toleranceof a dikaryon was substantially greater than that of eitherof its constituent homokaryons. It was also found that differentisolates of P. palustris varied very widely in copper tolerance.