Figure 8.

Cytochemical Localization of H₂O₂ Using Cerium Chloride Staining of acd2 Mutant and PPIX-Treated Wild-Type Leaves.

(A) and (B) Twenty-day-old acd2 leaves with some spontaneous cell death were used. Note electron-dense deposits of cerium perhydroxidase, indicative of the presence of H₂O₂ in the chloroplast (A) and mitochondrial (B) outer membranes. The chloroplast and mitochondrion were structurally intact.

(C) and (D) Wild-type control leaves stained with cerium chloride.

(E) and (F) Wild-type leaves infiltrated with 50 μM PPIX for 24 h. Note the presence of H₂O₂ in the outer membranes of clustered mitochondria (E) and in starch grains of chloroplast (F) in cells adjacent to those that died.

(G) and (H) Protoplasts from 18-d-old wild-type leaves were treated with (H) or without (G) 10 μM PPIX for 5 h in the light and then fixed to make regular electron microscopy samples. Note that mitochondria became swollen and round in shape in a PPIX-treated cell (H) when compared with a control cell (G).

These experiments were repeated three times with similar results. Ch, chloroplast; CW, cell wall; M, mitochondrion; S, starch grain. Bars = 1 μm in (A), (C), and (F) and 200 nm in (B), (D), (E), (G), and (H).