Figure 10.

Catalase activity, H₂O₂ contents, and subcellular H₂O₂ distribution in leaves exposed to different light regimes. Catalase activity in nkat/g dry weight, hydrogen peroxide (H₂O₂) contents in nmol/g dry weight and visualized by CeCl₃-staining on the subcellular level. Data in graphs show means with standard errors and document the activity of catalase and the amount of H₂O₂ detected in leaves of the wildtype (Col-0), the pad2-1 and the vtc2-1 mutants exposed to light conditions of 150, 300 and 1,500 μmol m^-2 s^-1 for 4 h (A, C) or 14 d (B, D). Data are means with standard errors of three analysis of three pooled samples of 10 leaves from a minimum of six different plants. Different lowercase letters indicate significant differences (P < 0.05) analyzed with the Kruskal-Wallis test followed by post-hoc comparison according to Conover. TEM-micrographs show the subcellular distribution of H₂O₂ visualized by CeCl₃-staining in leaves of Arabidopsis thaliana [L.] Heynh. ecotype Columbia (Col-0) exposed to light conditions of 150 and 1,500 μmol m^-2 s^-1 for 4 h. Strong CeCl₃-staining along the tonoplast, inside vacuoles (arrowheads), the cytosol (arrows), and cell walls (CW) was observed when plants were exposed to 1,500 μmol m^-2 s^-1 for 4 h. Staining was only found occasionally in CW of plants raised in control conditions. C = chloroplasts with or without starch (St), M = mitochondria, V = vacuoles. Bars = 1 μm.