Fig. 4
From: Macro- and microscopic leaf injury triggered by ozone stress in beech foliage (Fagus sylvatica L.)
Cellular and subcellular changes caused by oxidative stress within foliage of beech trees. Changes within palisade cells underlying bronzing (f–j), stippling (k–s) and yellowish dots (t–x) versus asymptomatic material (a–e). Bronzing symptoms (f–j): the adaxial chloroplasts (ad ch, g) contained more plastoglobules (pg) but fewer grana than abaxial organelles (ab ch, h). Plastoglobules were larger and grana stacks smaller. Nucleus (n) content was condensed and its envelope electron-opaque (i). j condensed cytosol (c) and injured matrix and inner membrane system (+) within the mitochondria (mt). Stippling symptoms (k–s): the severity of degenerative traits in chloroplasts (l, m), nucleus (n) and cytoplasm (o) was enhanced. k Fewer chloroplasts adaxially and vacuole filled with oxidized tannin bodies (*) often plugging the adaxial cell lumen. Occasionally, partial cell decompartmentation (~), shrinking vacuoles (shv) and cytorrhysis (arrowheads) indicated terminal cell degeneration and cell death. HR-like traits (p–s): cells were cytorrhyzed (arrowheads) and their content disrupted (p), chloroplasts (q, s) together with other organelles and cell structures (s) condensed and deformed, and extensive membrane damage was indicated by poor membrane resolution. Some material had been leaked into the periplasm (pe) through ruptured plasmalemma (pl). r Pyknotic nucleus showing deformation and acute chromatin condensation. Yellowish dots (t–x): cytorrhyzed and condensed (#) versus deformed and degenerated (§) strands (t). Within the latter group of cells (§; u, x), the chloroplasts showed degenerative traits (i.e. thinner grana and higher plastoglobule density). Within the former group of cells (#; v, w), the chloroplasts were condensed and deformed, their grana poorly resolved and the plastoglobules still small. w Pyknotic nucleus. x Intercellular material (im) leaked from adjacent dead cells. Other structures: cw: cell wall, d: dictyosome, l: lipid droplet, re: smooth endoplasmic reticulum, st: starch, v: vacuole. Technical specifications: postfixation using OsO4, contrasting using uranyl acetate and lead citrate, observation in TEM