Ultrastructure in Bean leaves infiltrated with bacterial extracellular polysaccharides

Ultrastructural observations were carried out in bean leaf tissue infiltrated with bacterial extracellular polysaccharides. These investigations revealed changes in the cell fine structure, especially related with chloroplast organization. Up to 24 h after EPS infiltration alterations consisted in irregularly running thylakoids and distortions of stacked regions. Invaginations of the plastid envelope and appearance of cytoplasm pockets inside the stroma were also noted. The most severe alterations, consisting in stroma dilations and envelope infoldings, were noted 24 h after EPS infiltration, paralleling the yellowing of the treated leaf areas; chloroplast shrinkage and collapse of thylakoid system were also sometimes observed. Chloroplast ultrastructure generally recovered 48 h after treatment; at this time local detachment of the plasma membrane and vesicle formation in the periplasmic space were observed, resembling a non specific, localized cellular response. The observed, permanent chlorosis and ultrastructural alterations suggest an interference of the EPS in the global metabolism of the bean mesophyll cell.