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Populations of the serpentine-endemic nickel-hyperaccumulator Alyssum bertolonii from nine different outcrops were investigated for differences in their nickel tolerance and accumulation levels and shoot:root ratio of nickel concentration. Plantlets from the different populations were cultivated in hydroponics culture and subjected to a range of nickel concentrations. For populations of this obligate serpentinophyte, the results showed significant intra-specific differences in the degree of both nickel tolerance and nickel accumulation. Among populations there was no correlation between the patterns of shoot and root tolerance, whereas there was a clearly correlated pattern for root and shoot nickel accumulation. The populations of this hyperaccumulator showed a significant variation also in shoot:root ratio in nickel concentration, but there was no relationship between this trait and shoot nickel accumulation levels. Regarding the still obscure relationship between metal tolerance and hyperaccumulation, our results demonstrated a strong positive linear relationship between these two phenomena in the nickel hyperaccumulator Alyssum bertolonii. [Copyright &y& Elsevier]

The patterns of variability in shoot metal concentrations within and among different populations of the serpentine endemic nickel-hyperaccumulator Alyssum bertolonii were evaluated and the relationship between plant element concentrations and both soil metal concentrations and genetic diversity was investigated. Metal concentration was determined in 180 plants and in the relative soils from nine populations of A. Bertolonii sampled on nine serpentine outcrops of Tuscany covering the whole distribution area of the species. The results indicated a high heterogeneity of metal concentration among soils and populations and a positive correlation for nickel in plants and soils. Moreover, an evident relationship between Ni concentration heterogeneity and genetic differentiation was found. Genetic diversity also correlated with the Ni variability of soils. In conclusion this field survey highlighted the large extent of polymorphism associated with Ni concentration of A. Bertolonii probably due to both soil properties and genetic basis. These data should be taken into consideration for careful management of plant germplasm with a view to conserving and exploiting the hyperaccumulating capacity. [Copyright &y& Elsevier]

Abstract Metal-contaminated sites can occur naturally in serpentine outcrops or as consequence of anthropogenic activities, such as mining deposits, aerial fallout from smelters and industrial processes. Serpentine outcrops are characterized by high levels of nickel, cobalt and chromium and present a typical vegetation which includes endemisms and plants which also live in uncontaminated soils. These latter metal-tolerant populations provide the opportunity to investigate the first steps in the differentiation of plant populations under severe selection pressure and to select plants to be used in the phytoremediation of industrially contaminated soils. In this report eight populations of Silene paradoxa L. (Caryophyllaceae) growing in copper mine deposits, in serpentine outcrops or in noncontaminated soil in central Italy, were analysed using random amplified polymorphic DNA (RAPD) markers to investigate the pattern of genetic variation. The genetic diversity observed in populations at copper mine deposits was found to be at least as high as that of the neighbouring serpentine populations. Analysis of molecular variance (amova) of the RAPD markers gave high statistical significance to the groupings of populations according: (i) with their geographical location; and (ii) with the metals present in the soil of origin (copper vs. nickel), indicating that RAPD markers detected a polymorphism related to the soil contamination by copper. Finally, two RAPD bands exclusive to copper-tolerant populations were identified. [ABSTRACT FROM AUTHOR]

Onosma echioides is a non-obligate serpentinophytic borage occurring discontinuously on calcareous and serpentine outcrops at the northwest limit of its range. Mean concentrations of Ca, Mg and heavy metals in root and shoot samples of eight populations from the two soil types were first determined. Subsequently, the genetic polymorphism of the same accessions was estimated by means of Amplified Fragment Length Polymorphism (AFLP) fingerprinting technique. Root and shoot samples from serpentine outcrops showed higher levels of Ni, Cr and Mg, and lower Ca/Mg ratios compared with those from calcareous soils. Based on 353 polymorphic AFLP bands, the two edaphic groups of populations showed comparable levels of genetic diversity. A remarkable genetic differentiation between populations and a high level of within-population genetic variance were found. Results of Mantel's test supported a significant correlation between genetic and geographical distances, while no difference in relation to the edaphic factor was detected. Molecular data suggested isolation as the key factor shaping the infraspecific genetic structure of O. echioides , which may be in relation with the short-distance, zoochorous systems of seed dispersal and pollination of this species. [ABSTRACT FROM AUTHOR]

Two independently evolved cupricolous populations, their ancestral serpentine population, another unrelated serpentine population and a non-metallicolous population of Silene paradoxa L. were compared for copper tolerance and foliar transcript levels of a 2b-type metallothionein gene that was previously shown to be involved in copper tolerance in the congener, S. vulgaris. The levels of copper tolerance and constitutive MT2b expression, assessed by Northern-blot analysis and semiquantitative RT-PCR, were proportionally increased in the cupricolous populations, as compared to the serpentine and the non-metallicolous populations. Southern-blot analysis revealed amplification of the gene in the cupricolous populations, such as in S. vulgaris, which might account for the higher constitutive expression level. Since the cupricolous populations descended separately from a common serpentine ancestral population, these results imply that MT2b overexpression must have been independently evolved in both of them, again such as previously shown S. vulgaris. Thus, both in S. paradoxa and S. vulgaris, the MT2b locus appears to be a major target for natural selection imposed by soil copper toxicity. [ABSTRACT FROM AUTHOR]

Summary • Molecular phylogeny based on ribosomal internal transcribed spacer (ITS) sequences was studied to investigate the phyletic relationships among some nickel (Ni)-hyperaccumulating and nonhyperaccumulating species of the genus Alyssum in relation to their geographic distribution and Ni-hyperaccumulating phenotype. • Thirty-seven samples belonging to 32 taxa were analysed by sequencing the polymerase chain reaction-amplified ITS region and performing neighbor joining, maximum parsimony and maximum likelihood phylogenetic analyses. • The ITS region in the sampled species varied from 221 to 307 bp of ITS1 and from 194 to 251 bp of ITS2. A total of 765 characters was used to infer the phylogeny and the average nucleotide variation detected was 15.15%. • Nickel-hyperaccumulation could have been lost or acquired independently more than once during the speciation of the genus. The geographical location of species could not be related to phylogenetic affinities. [ABSTRACT FROM AUTHOR]

Summary • Chloroplast microsatellites (cpSSR) were used to analyze the patterns of genetic variation within and among populations of the serpentine endemic, Alyssum bertolonii . • Thirty-five different chloroplast haplotypes were identified in 90 plants sampled from nine populations originating from the four disjunct northern-Italian serpentine regions where the species is found. • High levels of genetic diversity were found within each of the populations sampled. Analysis of Molecular Variance (AMOVA) showed high degrees of differentiation among both different populations of the same serpentine region and different regions (Φ ST = 0.622, Φ CT = 0.252, respectively). • The results indicated that: each population was established by few founders and then subsequently differentiated the existing chloroplast haplotypes; each population is a distinct genetic entity; and populations within the same serpentine region are more related than populations from different regions. [ABSTRACT FROM AUTHOR]

Abstract Eight populations of Silene paradoxa L. (Caryophyllaceae) growing in copper mine deposits, in serpentine outcrops or in uncontaminated soil in central Italy were studied. Genetic diversity was estimated using five polymorphic chloroplast microsatellite loci (cpSSR), identifying 27 different chloroplast haplotypes. The effective number of alleles, the haplotypic diversity and a stepwise mutational model-based parameter (DSH2) were computed. The effective number of alleles observed within populations from copper mine deposits was 20% that of the serpentine neighbouring populations, suggesting the occurrence of a founder effect. Moreover, 13 of the 27 different haplotypes scored were exclusive to only one population, indicating genetic isolation for all tolerant populations. Even the copper-tolerant populations appeared to have evolved independently. Finally, analysis of molecular variance (amova) of the cpSSR markers gave statistical significance to the grouping of populations according to their geographical location. This study demonstrates that cpSSR markers could be a useful complementary tool to isoenzymes or random amplified polymorphic DNA markers for elucidating the pattern of genetic differentiation in heavy metal-tolerant populations. [ABSTRACT FROM AUTHOR]