An application of EDXRF on the study of barley seedlings growth on sewage sludge

Genetic analyses of nickel tolerance in a North American serpentine endemic plant, Caulanthus amplexicaulis var. barbarae (Brassicaceae)

PREMISE OF THE STUDY

The evolution of metal tolerance in plants is an important model for studies of adaptation to environment, population genetics, and speciation. Here, we investigated nickel tolerance in the North American serpentine endemic Caulanthus amplexicaulis var. barbarae in comparison with its nonserpentine sister taxon C. amplexicaulis var. amplexicaulis. We hypothesized that the serpentine endemic would have a heritable growth advantage on nickel-containing substrates.

METHODS

We employed an artificial growth assay to quantify biomass accumulation. Study plants were crossed to create an F(2:3) population that was used to determine the heritability of nickel tolerance and to map quantitative trait loci (QTL). Nickel accumulation in both laboratory populations and native specimens was examined using energy-dispersive x-ray fluorescence (EDXRF).

KEY RESULTS

The serpentine endemic had a dramatic growth advantage at concentrations of nickel >30 µmol/L. Caulanthus amplexicaulis var. barbarae and its nonserpentine sister taxon both accumulated nickel to substantial levels. Nickel tolerance was highly heritable (h(2) = 0.59) and not associated with accumulation. The QTL analyses identified two major loci for nickel tolerance, on linkage group 2 (LG2) and linkage group 9 (LG9).

CONCLUSIONS

In our study, nickel tolerance was determined by two major loci with large effects. At both loci, alleles from the serpentine parent conferred positive effects on nickel tolerance, suggesting that they are adaptive in the natural serpentine environment. The mechanism of nickel tolerance in the serpentine plant was not exclusion of nickel. Nickel tolerance may have an inducible component in C. amplexicaulis var. barbarae.

Hormone-like activity of humic substances in Fagus sylvaticae forests

• Soil A horizons from a large area typical for beech (Fagus sylvatica) in northern Italy were investigated to understand the phyto-hormone-like activity of humic substances (HS) with respect to the vegetation. These soils had developed under thermophilous (Cephalonthero-Fagion with Carici albae-Fagetum), mesophilous (Fagion sylvaticae with Dentario pentaphylli-Fagetum and Galio-odourati-Fagetum) or acidophilous (Luzulo-Fagion with Luzulo niveae-Fagetum) beech forests. • The development of organic and humic matter in the three forest types was assessed by quantifying chemical parameters. Phyto-hormone-like activity of HS was evaluated by measuring auxin-like (IAA_like ) and gibberellin-like (GA_like ) activity as well as IAA concentration, invertase and peroxidase activities. • Soil pH differed between the forest types. Soil C: N distinguished the thermophilous and the mesophilous from the acidophilous types but did not distinguish thermophilous from the mesophilous types. Phyto-hormone-like activity of HS varied significantly across the beech forests. Acid conditions were essential for the release of IAA_like activity whereas neutral conditions promoted GA_like activity. Plant isoenzymatic polymorphism confirmed the different auxin activities of HS. • The phyto-hormone-like activity of HS is highly suitable, and better than soil chemical parameters, for differentiating between these ecosystems.