No abstract

Ni2+ toxicity was evaluated in Triticum aestivum L. by its effects on root and shoot length, dry matter production and water content. Over a threshold value of 20 mmol m−3 Ni2+ the degree of toxicity increases as a function of the Ni2+ concentration in the medium. Ni2+‐treated roots show enhanced lipid peroxidation; the higher Ni2+ treatment (40mmol m−3) also increases leakage of K+. In roots and shoots, Ni2+ enhances both guaiacol and syringaldazine extracellular peroxidase activity. The increase in extracellular peroxidase activity is also associated with an increase in the phenolic contents of roots and shoots. The observed growth inhibition might be partly the result of the effect of Ni2+ on cell turgor and cell‐wall extensibility. Intracellular soluble peroxidases are also stimulated by Ni2+; such effects, independently of the substrate, were detected in extracts of Ni2+‐treated shoots at a lower Ni2+ concentration than in the roots. Intracellular peroxidases might act as scavengers of peroxide radicals produced as a result of nickel toxicity.

occurrence of a non-reciprocal co-tolerance mechanism. The Three Tuscan ecotypes of Silene paradoxa L. were studied to evaluate the occurrence of multiple tolerance or co-tolerance nickel-tolerant population seemed able to tolerate nickel by limiting its inhibiting effect on the peroxisomal H 2 O 2 scavengmechanisms and to underline some tolerance strategies in plants naturally adapted to toxic concentrations of heavy ing enzymes since, in the sensitive population, this inhibition revealed itself as one of the causes of nickel-induced oxidative metals. Seeds were collected from non-toxic calcareous soil, a stress. A very low copper root and shoot concentration seemed serpentine outcrop with high nickel content and a copper mine to be characteristic of the copper-tolerant population, comdump. The evaluation of the toxic effects of the metals on root bined with a low susceptibility to metal-induced oxidative growth showed the copper-tolerant population as nickel co-tolerant, whereas the opposite was not the case. This suggests the stress.

We report the isolation and characterization of endophytic bacteria, endemic to serpentine outcrops of Central Italy, from a nickel hyperaccumulator plant, Alyssum bertolonii Desv. (Brassicaceae). Eighty-three endophytic bacteria were isolated from roots, stems, and leaves of A. bertolonii and classified by restriction analysis of 16S rDNA (ARDRA) and partial 16S rDNA sequencing in 23 different taxonomic groups. All isolates were then screened for siderophore production and for resistance to heavy metals. One isolate representative of each ARDRA group was then tested for plant tissue colonization ability in sterile culture. Obtained results pointed out that, despite the high concentration of heavy metals present in its tissues, A. bertolonii harbors an endophytic bacterial flora showing a high genetic diversity as well as a high level of resistance to heavy metals that could potentially help plant growth and Ni hyperaccumulation.

In the present study, heterotrophic nickel-resistant bacteria were isolated and characterized from three different serpentine outcrops in central Italy populated by the nickel-hyperaccumulating plant Alyssum bertolonii. Bacteria were isolated from the rhizosphere of the plant and from soil portions at various distances from the plant. The proportion of nickel-resistant cfu was higher in proximity to the plant than in free soil. A total of 138 isolates was collected and grouped into 47 different operational taxonomic units (OTUs) by means of amplified ribosomal DNA restriction analysis (ARDRA) and into 25 heavy-metal resistant phenotypes. The phylogenetic position of strains belonging to 20 OTUs, representing more than the 70% of the total isolates, was determined by 16S rDNA sequencing. These analyses showed that the most represented genera in all three different outcrops were Pseudomonas and Streptomyces. Pseudomonas strains were found to be predominant in the plant rhizosphere, whereas Streptomyces strains were mainly present in the soil.