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The lead absorbed by the roots induce oxidative stress conditions through the Reactive oxygen species (ROS) production for the pea plants cultivated hydroponically for 96 h on a Hoagland medium with the addition of 0.1 and 0.5 mM of Pb(NO₃)₂. The alterations in O₂⁻˙ and H₂O₂ concentrations were monitored spectrophotometrically which show a rapid increase in O₂⁻˙ production during the initial 2 h, and in case of H₂O₂, during the eighth hour of cultivation. The level of ROS remained higher at all the time points for the roots of the plants cultivated with Pb²⁺ and it was proportional to metal concentration. The production of O₂⁻˙ and H₂O₂ was visualized by means of fluorescence microscope technique. They are produced in nonenzymatic membrane lipid peroxidation and its final product is Malondialdehyde, the level of which increased together with the level of H₂O₂. As stress intensity raised (duration of treatment and Pb²⁺ concentration), so did the activities of superoxide dismutases, catalase and ascorbate peroxidase antioxidative enzymes and of low-molecular antioxidants, particularly glutathione (GSH), homoglutathione (h-GSH) and cysteine substrate toward their synthesis. The root cells redox state (GSH/GSSG) dropped proportionally to lead stress intensity.
The ever-increasing environmental pollution necessitates organisms to develop specific defense systems in order to survive and function effectively. Lead is taken up by plants mainly through roots and over 96% are accumulated there.Pea plants were cultivated hydroponically for 4 days with 0.1, 0.5 and 1 mM Pb(NO3)2. Uptake of lead ions from nutrient solution and accumulation in root stems and leaves during 96-h cultivation was estimated. The root tip cells were observed with transmission electron microscope to analyse their ultrastructure and lead localization. Pb was accumulated in the cell wall, cell membrane, vacuoles, mitochondria and peroxisomes. The fractions of mitochondria and peroxisomes were isolated from pea roots purified by means Percoll gradient, and were observed by means of electron microscope with the attachment for X-ray microanalysis. Visible deposits containing Pb were observed in both cell organelles.
Reactive oxygen species (ROS) production and enzymatic antioxidative system [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX), alternative oxidase (AOX)] in nonphotosynthesizing pea plant cells were investigated. From the roots of pea plants cultivated hydroponically on a Hoagland medium with the addition of 0.1 and 0.5 mM of Pb(NO₃)₂, the three following fractions were isolated by means of a Percoll gradient: cytosol, peroxisomal, and mitochondrial. Lead stress caused H₂O₂ production in these organelles. The mitochondria from pea cell roots were the main site of H₂O₂ production. Intensive stress caused by 0.5 mM of Pb(NO₃)₂ brought about a decrease of H₂O₂ concentration in mitochondria and peroxisomes after 3 days of the exposition, which was due to an increase of CAT activity. The isoenzymatic profile of antioxidative enzymes indicates mitochondrial and peroxisomal localization of MnSOD and cytoplasmic localization of CuSOD. APOX activity was estimated for all three fractions: cytosol, mitochondria, and peroxisomes. Simultaneously, we observed an increased expression of AOX genes on the basis of the amount of mRNA transcript and confirmed it immunologically on the level of synthesized AOX protein (36 kDa). This has been the first evidence of AOX genes expression of which is induced by the treatment of plants with lead ions and it increases along with the concentration of metal.
The presence of the single metals (Cd, Pb, Cu, Zn) induces ROS (reactive oxygen species) production and causes oxidative stress in plants. While applied in two-element combinations, trace metals impact organisms in a more complex way. To assess the resultant effect we treated the pea grown hydroponically with the trace metals in variants: CuPb, CuCd, CuZn, PbCd, ZnPb, ZnCd in concentrations of 25 µM for each metal ion. Abiotic stress inhibited root elongation growth, decreased biomass production, induced changes in root colour and morphology. It changed rate of ROS production, malondialdehyde content, increased activity and altered gene expression of defence enzymes (superoxide dysmutase, catalase, ascorbate peroxidase, glutathione reductase, γ-glutamylcysteine synthetase).
Heavy metals (Cd, Pb, Cu, Zn) absorbed by roots brought about oxidative stress conditions through ROS production (O₂¯˙, H₂O₂) for pea plants cultivated hydroponically for 96 h on a Hoagland medium with the addition of 50 μM: CdCl₂, Pb(NO₃)₂, CuSO₄, and ZnSO₄. We shows, using laser ablation ICP MS, that Cd, Cu, Pb, and Zn elements are located along a cross-section through the roots of pea plants. We observed increasing activities of antioxidative enzymes (SOD, CAT, GR) in oxidative stress conditions. We have shown changes in redox state (GSH/GSSG) in pea root grown with Pb, Cu, Cd, and Zn.
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