FIGURE 5.

Transmission electron micrographs of orange leaf (C. sinensis cv. Valence) inoculated with 10⁸ CFU mL^-1 Xcc 306. (A) Leaf of non-inoculated plant, showing complete absence of Xcc 306 cells and EPS in the intercellular space of mesophyll cells. Inset shows an intact cell wall at higher magnification. (B) Control not treated with F3d 120 h after inoculation, showing the intercellular space colonized with Xcc 306 and EPS evidenced by the electron-dense appearance. Inset shows viable bacterial cells present in the intercellular space in contact with host cell wall and disruption process at higher magnification. (C) The 120 h after inoculation in the preventive treatment; non-viable Xcc 306 cells are shown at the entrance of outer stomatal chamber and substomatal chamber. (D) After 120 h of preventive treatment, few bacterial cells are seen in the leaf mesophyll, with altered bacterial cell morphology and different electron-dense appearance in intercellular space (suggesting absence of EPS). (E) After 120 h of inoculation in the preventive treatment, higher magnification of Figure 4D, showing the presence of non-viable Xcc 306 cells in the substomatal chamber. (F) After 120 h in the curative treatment, the same effects are seen when compared with preventive treatment on orange leaves, including the effect on bacterial cells. (G) Mesophyll cells are unaltered and bacterial cells (Xcc 306) appear lysed, with different electron-dense appearance in intercellular space (suggesting absence of EPS). (H) Presence of non-viable Xcc 306 cells in the intact mesophyll cell and absence of EPS at higher magnification of Figure 4F. (CW, host cell wall; IS, intercellular space; SC, substomatal chamber; VB, viable cell; V, vesicle; arrowhead, non-viable Xcc 306 cell).