Establishment of callus and cell suspension cultures from Gypsophila paniculata leaf segments and study of the attachment of host cells by Erwinia herbicola pv. gypsophilae

Callus and cell suspension cultures were initiated from leaf segments of G. paniculata. Fresh and dry weights measurements of callus showed that callus growth was optimal on MS medium supplemented with 1.0 mg l^–1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.2 mg l^–1 benzyladenin (BA). Calli cultured on this medium, showed a two-fold increase in fresh weight by the fourth week of incubation. The initiated hard green callus was repeatedly subcultured on MS medium containing increasing concentrations of 2,4-D in order to increase its friability. The friable callus was then used for establishment of a cell suspension culture. Maximum growth of the suspension culture was on medium supplemented with 1.0 mg l^–1 2,4-D and 0.2 mg l^–1 BA.The suspension culture was used for studying plant host attachment in both electron and light microscopy. Upon infection with E. herbicola, plant cells showed aggregate formation within 24 h of infection. In the presence of the pathogenic Ehg,the number of aggregates formed was 342 aggregates ml^–1, in the presence of the non-pathogenic Ehg154 aggregates ml^–1 and in the control 115 aggregates ml^–1. These results show that the pathogenic strain causes formation of cell aggregates 5.8 times greater than the non-pathogenic one. Based on these results, it can be hypothesized that bacterial cells of the pathogenic strains bind to the plant cells and may form a bridge for attachment of plant cells to one another. Observations by electron microscope show that bacterial cells do attach to plant cells and that this attachment might be via formation of a bridge between the bacteria and the plant cell.