Figure 8.

Cytochemical Localization of Wound-Inducible H₂O₂ in Vascular Bundles of Tomato Leaves.

(A) Electron-dense deposits of CeCl₃ indicative of the presence of H₂O₂ in developing secondary cell walls of xylem vessels (XV) of control unwounded leaves (arrows show typical deposits). Note that the cell walls of an adjacent vascular parenchyma cell (VP) show little CeCl₃ staining.

(B) Absence of CeCl₃ staining in the cell walls of vascular parenchyma (VP) and neighboring spongy mesophyll (SM) cells associated with the phloem in control unwounded leaves.

(C) H₂O₂ generation in the vascular bundle of a wounded tomato leaf 4 hr after wounding. H₂O₂ accumulates strongly in the cell walls of vascular parenchyma cells bordering spongy mesophyll cells and at the intercellular spaces (IS).

(D) Systemic accumulation of H₂O₂ in vascular bundles of upper unwounded leaves of young tomato plants 4 hr after wounding of the lower leaf.

CC, companion cell; CW, cell wall; SE, sieve element. .