FIGURE 4.

Changes in the distribution of H₂O₂ as revealed by DCF fluorescence under a confocal scanning microscope in the pedicel (A–E) and by CeCl₃ precipitation in the abscission zone under a transmission electron microscope (F–P) after girdling plus defoliation treatment. A,F,L: samples at day 0 (control), with occurrence of H₂O₂ that was more concentrated in the cambium (arrow in A) and exclusively located in the cell walls (arrows in F); B,G,M: samples of 1 day after treatment (DAT). Note increase in fluorescence yield compared with that at Day 0 (B vs A) and apoplastic location of H₂O₂ along the plasma membrane (arrows) and the cell walls (arrows in G and M). C,H,N: samples of 2 DAT. Note fluorescence reduced compared with 1 DAT (C vs B) and H₂O₂ occurred exclusively in the cell walls (arrows in H). D,I,O: samples of 3 DAT, with fluorescence weaker than in the earlier samples and no observable occurrence of H₂O₂ in the cell walls and other cell parts. Note apparent breakdown of cytoplasm and plasma membrane (red arrow in O). E,J,P: samples of 4 DAT, with reappearance of H₂O₂ in the cell walls and mitochondria (white arrows in P) and breakdown of plasma membrane (red arrows in P). Dashed lines indicate the abscission layer. The symbol “#” indicates the abscission zone with relatively high H₂O₂. cw, cell wall; ch, chloroplast; m, mitochondrion; mi, microsome; n, nuclear; o, oil drop in chloroplast; s, starch grains in chloroplasts; v, vacuole.