COPPER-INDUCED OXIDATIVE STRESS IN MAIZE SHOOTS ( ZEA MAYS L.): H 2 O 2 ACCUMULATION AND PEROXIDASES MODULATION

The effect of copper excess on growth, H 2 O 2 level and peroxidase activities were studied in maize shoots. Ten-day-old seedlings were cultured in nutrient solution that contained Cu 2+ ions at various concentra- tions (50 and 100 μM) for seven days. High concentrations of Cu 2+ ions caused significant decrease both in matter production and elongation of maize shoots. In addition, treatment with CuSO 4 increased levels of H 2 O 2 and induced changes in several peroxidase activities. Moreover, the disturbance of the physio- logical parameters was accompanied by the modulation of the peroxidase activities: GPX (Guaiacol per- oxidase, EC 1.11.1.7), CAPX (Coniferyl alcohol peroxidase, EC 1.11.1.4) and APX (Ascorbate peroxi- dase, EC.1.11.1.11). Furthermore, this modulation becomes highly significant, especially, in the presence of 100 μM of CuSO 4

EFFECT OF COPPER EXCESS ON H 2 O 2 ACCUMULATION AND PEROXIDASE ACTIVITIES IN BEAN ROOTS

We studied oxidative stress and peroxidase activity resulting from application of excess copper in the nutrient medium on the roots of young bean seedlings. The change in H 2 O 2 content, lipid peroxidation and antioxidant enzymes activities were quantified and located. Excess of copper caused a loss of mem- brane integrity and the formation of hydrogen peroxide (H 2 O 2 ) as visualized in the transmission electron microscopy and measured using spectrophotometry. H 2 O 2 accumulated in the intercellular spaces and in the cell wall. The production of H 2 O 2 was accompanied by an increase in the activity of soluble and ionic GPX (guaiacol peroxidase, EC 1.11.17), CAPX (coniferyl alcohol peroxidase) and NADH oxidase

Cupric stress induces oxidative damage marked by accumulation of H2O2 and changes to chloroplast ultrastructure in primary leaves of beans (Phaseolus vulgaris L.)

The effect of copper excess (CuSO4) on lipid peroxidation, H2O2 content, and antioxidative enzyme activities was studied in primary leaves of bean seedlings. Fourteen-day-old bean seedlings were cultured in a nutrient solution containing Cu2+ at various concentrations (50 and 75 µM) for 3 days. Excess of copper significantly increased malondialdehyde content and endogenous H2O2. This radical accumulated in the intercellular spaces of palisade mesophyll cells. In addition, cupric stress induced changes in antioxidant enzyme activities. GPX (guaiacol peroxidase, EC 1.11.1.7) activity was decreased in 50 µM Cu-stressed leaves whereas 75 µM of CuSO4 resulted in an increase of enzyme activity. On the contrary, CAT (catalase, EC 1.11.1.6) activity was stimulated at 50 µM CuSO4 but unaltered at 75 µM CuSO4. Transmission electron microscopy revealed that excess copper induced changes in the ultrastructure of chloroplasts visible in form of a deterioration in the grana structure and the accumulation and swelling of starch grains in the stroma

Study of the partial decomposition of GaN layers grown by MOVPE with different coalescence degree

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Investigations of in situ reflectance of GaN layers grown by MOVPE on GaAs (001)

International audienceThe growth of low temperature GaN (LT-GaN) layers on GaAs (0 0 1) substrate was performed by metal organic vapor phase epitaxy (MOVPE) at growth temperature range of 500–800 °C. Laser reflectometry (LR) was employed for in situ monitoring of all growth steps. The simulation of experimental time reflectance traces shows that at the first growth stage, the surface roughness increases to reach a limit value depending on growth temperature. Due to surface roughness profile the growth rate time-dependence was found non negligible at the first growth stage. The investigations of in situ reflectance give more precise measurement of growth rates that yields to thermal activation energy close to 0.12 eV. The ex-situ analyses by spectral reflectance (SR) and Atomic Force Microscopy (AFM) showed that the better surface morphology was obtained when the GaN buffer layer is grown at lower temperature, while three dimensional (3D) growth mode was observed at higher temperature. A series of high temperature (800 °C) GaN (HT-GaN) layers were grown on different thicknesses of low temperature (550 °C) GaN buffer layer. The results showed that high density of nucleation sites enhances the initial growth rate and improves the morphological quality of GaN active layer