Abstract
This study evaluates in vitro tolerance of white poplar genotypes to the presence of lead in an acidic rooting medium. Lead was supplemented in form of Pb(NO3)2, in the following concentrations: 0 M (Control), 10-6 M, 10-5 M, 10-4 M and 10-3 M. After four weeks of cultivation, the following characters were measured: number of roots, the length of the longest root, the shoot height, dry root mass and dry shoot mass, and parameters related to photosynthetic pigments: content of chlorophyll a, b, a+b, and of carotenoids in fresh mass, as well as chlorophyll a/b ratio. For further statistical analysis, tolerance indices by Turner and Marshal (TI) were calculated for each measured character. The strongest inhibitory effect was achieved on the medium with 10-4 M Pb(NO3)2, but the best differentiation between genotypes was achieved on the medium with 10-5 M Pb(NO3)2. The highest tolerance indices for the length of the longest root and shoot height had genotypes L-12 and LBM, and for root and shoot dry mass genotypes LCM and L-12. There were no significant differences between genotypes in tolerance indices by any of the examined photosynthetic parameters. The obtained results suggest that both low pH and the presence of citric acid as chelating agent improved evaluation of lead tolerance in comparison with the results obtained on media with standard pH and without citric acid in similar studies. In vitro tests on acidic medium with citric acid can efficiently differentiate examined genotypes for lead tolerance, which could be important for their use in phytoextraction projects, especially on acidic soils.
Highlights
With the start of the rapid development of mining and industrialization at the end of the 19th century, the ecosystems have been constantly polluted by a wide variety of heavy metals (Benavides et al 2005)
Lead naturally occurs in the soil, but its content can be greatly increased by human activities (Seregin and Ivanov 2001)
Since there was no significant effect of factor Medium, as well as of interaction Genotype × Medium on tolerance index based on the number of roots, data from further statistical analysis for this parameter are not presented
Summary
With the start of the rapid development of mining and industrialization at the end of the 19th century, the ecosystems have been constantly polluted by a wide variety of heavy metals (Benavides et al 2005). Lead is a heavy metal that is considered one of the most toxic metals (Zhang 2003), and the major pollutant in both terrestrial and aquatic ecosystems (Sharma and Dubey 2005). Apart from negative effects on membrane structure, water potential, and hormonal status, its toxicity is mostly related to oxidative stress by increased accumulation of free radicals and reactive oxygen species. Lead stimulates this process by affecting enzyme activity and inhibition of electron transport during oxidative phosphorylation (Seregin and Ivanov 2001, Sharma and Dubey 2005, Zengin and Munzuroglu 2005)
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