Treatment with 50 µM CuSO 4 for five days caused significant decrease in dry-matter production and protein level of tenday-old sunflower seedling roots. An increase of lipoperoxidation product rate was also observed. The involvement of some enzyme activities in the sunflower root defence against Cu-induced oxidative stress was studied. Copper treatment induced several changes in antioxidant enzymes. SOD (superoxide dismutase, EC 1.15.1.1) activity was reduced but CAT (catalase, EC 1.11.1.6) and GPX (guaiacol peroxidase, EC 1.11.1.7) activities were significantly enhanced. The lignifying peroxidase activities, assayed using coniferyl alcohol and syringaldazine, were also stimulated. Analysis by native gel electrophoresis of syringaldazine peroxidase activity showed the stimulation of an isoform (A2) and the induction of another one (A1) under cupric stress conditions. On the other hand, the activity of PAL (phenylalanine ammonia lyase, EC 4.3.1.5), which plays an important role in plant defence, was also activated. The possible mechanisms by which Cu-induced growth delay and changes in enzymatic activities involved in plant defence processes are discussed. To cite this article: H.
The term ''peroxidase'' designs a group of hemoproteins with a wide structural variability. These enzymes catalyze the redox reaction between hydrogen peroxide and some reductors. They can be found in animals, plants and microorganisms. In plants, peroxidases are involved in numerous cellular processes such as development and stress responses. In fact, they are involved in growth regulation by controlling hormonal and cell wall metabolism and antioxidant defense. On the other hand, these enzymes are considered as a biomarker indicating biotic and abiotic stresses. Under metallic stress conditions, the quantitative and qualitative profiles of peroxidases are generally modified. Such modulations could prove the major role played by these enzymes in the defense mechanism. In this paper, we discussed the variation of isoperoxidases behavior under metallic stress conditions.
Copper is both a nutrient and an environmental toxin that is taken up by plants. In order to determine the subcellular localization of copper and to assess the resulting metabolic changes, we exposed 14-day-old bean seedlings to nutrient solutions containing varying concentrations of Cu(2+) ions for 3 days. Biochemical analyses revealed that the cell wall was the major site of Cu(2+) accumulation in the leaves of treated plants. Excess copper modified the activity of lignifying peroxidases in both soluble and ionic cell wall-bound fraction. The activity of ionic GPX (guaiacol peroxidase, EC 1.11.1.7) was increased by 50 and 75 µM CuSO₄. The activities of both ionic CAPX (coniferyl alcohol peroxidase, EC 1.11.1.4) and NADH oxidase were increased by both copper concentrations tested. While soluble CAPX activity decreased in leaves treated by all copper concentrations tested, the activity of soluble NADH oxidase remained unchanged at 50 µM and was enhanced at 75 µM. Treatment with CuSO₄ also increased the abundance of total phenol compounds and induced stimulation in the activity of PAL (phenylalanine ammonia lyase, EC. 4.3.1.5). Using histochemistry in combination with fluorescence microscopy we show that bean leaves from copper-exposed plants displayed biochemical and structural modifications reinforcing the cell walls of their xylem tissues. On the other hand, the perivascular fiber sclerenchyma appeared to be less developed in treated leaves.
Ab stractThe changes in lipid peroxidation, antioxidative and lig ni fy ing en zyme ac tiv i ties were stud ied in leaves and stems of Cu-stressed sun flower seed lings. In both or gans, mem brane lipid peroxidation was en hanced by cop per treat ment. Ad di tionally, catalase (EC 1.11.1.6) and superoxide dismutase (EC 1.15.1.1) ac tiv i ties were mod u lated: The ac tiv ity of superoxide dismutase was en hanced in both plant or gans. Dif fer ently, catalase ac tiv ity was not af fected in leaves but sig nif i cantly reduced in stems. Peroxidase (EC 1.11.1.7) ac tiv i ties were also changed. Guaiacol peroxidase ac tiv ity was in creased in leaves and stems. In the same way, elec tro pho retic anal y sis of the anionic isoperoxidases in volved in lig ni fi ca tion (syringaldazine peroxidase) re vealed qual i ta tive and quan ti ta tive changes on the isoenzyme pat terns. These mod i fi ca tions were ac com panied by the in crease of the NADH-oxidase ac tiv ity in ionically cell wall bound frac tion. It ap peared that the growth de lay caused by cop per ex cess could be re lated to the ac ti va tion of lig ni fy ing peroxidases.
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