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ŠUMARSKI LIST 5-6/2013 str. 23     <-- 23 -->        PDF

10(–7) M) in the same background so­lution (Hoagland’s solution). Cd did not cause serious disturbance of growth and physiological parameters in the studied poplar clones. With­in our results in shoots, Cd showed inhibitory effect on SOD activity, mostly on its high concentration applied in PE 19/66 and M1 clone. B 229 clone showed increasing level of SOD activity, indicating that this genotype has a significantly acceptable antioxidative answer to applied high concentration of heavy metal in soil. Previous investigations on species very close to poplars (Zacchini et al., 2009) showed that almost all selected willow clones, used to extract Cd2+, accumulated half of the absorbed metal in the aerial parts exhibiting a translocation factor twice respect to poplar clones, that on the contrary, accumulated much more Cd2+ than willow clones in the roots.
The high antioxidant activity was reported throughout the test period in specimens of species of Populus alba L. In this plant, the process of lipid peroxidation and accumulation of free proline was intensified in order to protect the leaves from oxidative damage in dry periods, especially during July. P. alba showed the highest antioxidant capacity in July, when the drought was the most severe and accumulation of antioxidant molecules was induced by stressful factor. (Štajner et al., 2011). This was a good example where Populus representatives showed acceptable antioxidative answer due abiotic stress. M1 and B229 clones showed their acceptable general anitoxidative activity within young shoots, despite they showed also variable results for different treatments. Antioxidative answer was noticeable indicating that it may range from moderate to high anitoxidative system activity within shoots, especially in M1 and B229 clones. Unfortunately, PE 19/66 in LPx parameter and decreased SOD activity showed weaker antioxidative answer to applied heavy metal treatments.
SOD activity was also measured by Nikolić et al. (2008). It showed decrease in roots and increased in the leaves of treated plants of hybrid poplar (Populus nigra × maximowitzii × P.nigra var. Italica), clone 9111/93. Cd-induced toxic effects (stunted growth, leaf chlorosis, oxidative stress) were observed, indicating that this clone was vulnerable to the pollutant. High amounts of Cd accumulated in roots, but in view of its low translocation from roots to aboveground parts, along with the disturbances in plant growth, this hybrid poplar showed little potential for use in remediation of sites contaminated with Cd. There is possibility that 9111/93 and PE 19/66 clone share similar genetic profile, because both of them showed unacceptable antioxidative answer on applied cadmium treatment, since it is well-known pollutant in soil. Poplar trees (Popullus deltoides x Populus cv caudina, NE clone 353) were used in studies of Sen Gupta and Alscher (1991) and showed both glutathione levels and superoxide dismutase activity increased before there was any observable ozone effect on photosynthesis.
Cd was found to produce oxidative stress (Hendry et al., 1992; Somashekaraiah et al., 1992), but, in contrast with other heavy metals such as Cu, it does not seem to act directly on the production of oxygen reactive species (via Fenton and/or Haber Weiss reactions) (Salin, 1988). On the other hand, Cd ions can inhibit (and sometimes stimulate) the activity of several antioxidative enzymes. In species such as Helianthus annuus leaves, Cd enhanced lipid peroxidation, increased lipoxygenase activity and decreased the activity of the following antioxidative enzymes: superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase (Gallego et al., 1996). In Phaseolus aureus, Cd ions produced lipid peroxidation, decrease of catalase activity and increase of guaiacol peroxidase and ascorbate peroxidase activity (Shaw, 1995).
Kebert et al. (2011) were also examining the effects of different types and concentrations of contaminants on the oxidative stress of several poplar clones. They analyzed the antioxidant capacity of poplar clones PE 19/66, B229 (Populus deltoides) clone and Pannonia (Populus x euramericana) in leaves after treatment with heavy metals, herbicides, diesel fuel and the combination of heavy metals and diesel fuel in the experimental field. They measured the total antioxidant capacity using the FRAP method and all three clones showed an increased total antioxidant capacity under conditions of increased quantities of pollutants compared to controls. Our results for B229 clone showed mostly decreased values of FRAP units on applied treatments, in shoots. PE 19/66 showed similar answer, but M1 showed increased FRAP values especially during nickel treatments. Those studies indicate that different anitoxidative answers may be gained regarding the analyzed organ. Leaves are metabolically very active organs, but shoots are mostly known of transporting the metabolites and nutrients on two ways and that may show less need of plants for antioxidative defense in shoots since the nutrients and other substances taken from soil rarely stayed inside it.
Trudić et. al 2012., showed variable responses within leaves and roots (taken from the same clones mentioned in our study) in response to oxidative stress induced by heavy metals (also Ni3+, Cu2+ and Cd2+) and the most promising clone for phytoremediation of contaminated soils is B229 clone, while M1 and PE 19/66 showed variable antioxidant response. The M1 clone showed a decrease in SOD values, FRAP and protein values, as well as an increase in MDA production at higher concentrations of heavy metals, indicating its weak resistance to greater contamination by heavy metals. Clone B229 mostly varied in response to oxidative stress, although its response to stress induced by high concentrations of heavy metal ions indicated that it was the most resistant to their presence, especially Cd. Compared to their control samples, the B 229 clone showed small changes in total protein and FRAP content, while the SOD activity in various organs was different.