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Cadmium (Cd), similarly to other heavy metals, inhibits plant growth. We have recently showed that Cd2+ either stimulates (1–4 uM) or inhibits ( 6 uM) growth of soybean (Glycine max L.) cells in suspension culture (Sobkowiak & Deckert, 2003, Plant Physiol Biochem. 41: 767–72). Here, soybean cell suspension cultures were treated with various concentrations of Cd2+ (1–10 uM) and the following enzymes were analyzed by native electrophoresis: superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and ascorbate peroxidase (APOX). We found a significant correlation between the cadmium-induced changes of soybean cell culture growth and the isoenzyme pattern of the antioxidant enzymes. The results suggest that inhibition of growth and modification of antioxidant defense reactions appear in soybean cells when Cd2+ concentration in culture medium increases only slightly, from 4 to 6 uM.
The effect of lead, cadmium and cooper on protein pattern, free radicals and antioxidant enzymes in root of Lupinus luteus L. were investigated. Heavy metals inhibited growth of lupin roots, which was accompanied by increased synthesis and accumulation of a 16 kDa polypeptide (Przymusiński et al. 1991 Biochem. Physiol. Pflanzen., 187:51–57). This component has been earlier identified as immunologically related to Cu,Zn-superoxide dismutase (Przymusiński et al. 1995 Env.Exp.Bot., 35:485–495). However, more detailed study revealed that this stress-stimulated protein is composed of four to six polypeptides of different electrophoretic mobility. The most abundant polypeptides of the 16kDa region were found to be closely homologous to pathogen related proteins. The number and intensity of these polypeptides was highly variable in roots of individual seedlings, which suggests that they might represent separate allelic forms. Electron paramagnetic spectra revealed that at low lead concentrations the amplitude of the first derivative was similar to the control and distinctly increased at higher metal concentrations. On the other hand, at the lower lead concentrations the activity of antioxidant enzymes increased, whereas at higher metal doses the enzyme activities did not raise further (SOD) or even dropped (CAT, APOX). This implies that the responses of antioxidant system to lead is dose-dependent stimulated by low metal concentrations, whereas at the higher metal level the free radical emission is beyond the quenching capacity of antioxidant enzymes, which in turn might contribute to the reduced root growth. The effect of various heavy metals: Pb²⁺, Cd²⁺ and Cu²⁺ on phytochelatins and antioxidant enzymes depends on the kind of metal ion. Pb²⁺ and Cd²⁺ stimulated the PCs formation whereas Cu²⁺ was not effective. On the other hand, in root exposed to Cu the activity of catalase (CAT) was the highest as was the production of H₂O₂. The strong oxidative effect of Cu²⁺ ions which were not complexed by PCs suggests that these peptides might by involved in the cellular defense system by binding excessive heavy metal ions. On the basis of our results it can be concluded that in lupin roots exposed to heavy metals there is a complex defense system against metal phytotoxicity, which comprises of specific proteins, antioxidant enzymes and phytochelatins.
This paper presents the results of a study on the influence of lead (Pb2+) on DNA integrity on plant cells. The study was performed on the root tips of lupin (Lupinus luteus cv. Juno) seedlings treated with two selected concentrations of Pb(NO3)2: 150 and 350 mg l-1, which were found to inhibit root growth by 50% and 70%, respectively [Ruciłska et al. Plant Physiol. Biochem. 37 (1999) 37187-37194]. Roots exposed to those external lead concentrations took up about 50 and 70 mg l-1 Pb2+ g-1 fresh weight (FW) over 48 h of incubation. A dose-dependent increase in the degree of root injury was observed in the presence of both tested concentrations. The genotoxicity of lead in lupin root cells was analysed using a mild alkaline comet assay at pH 12.3, which allows the detection of single strand breaks. The quantity of the DNA fragments migrating away from the nuclear remnant (tail area) increased proportionally to the lead content inside the roots, and was positively correlated with the degree of root injury. At 150 mg l-1 Pb2+, a high frequency distribution of nuclei having large values of tail lengths and moments was observed. By contrast, the number of nuclei with minimum values of these parameters increased at 350 mg l-1 Pb2+. This data suggests that lead at low concentrations induces the formation of short, rapidly migrating DNA fragments, whereas at higher concentrations, lead probably causes other changes to DNA that result in slower DNA migration in the electric field.
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