Attachment of Pseudomonas syringae onto Leaf Surface of Italian Ryegrass

The attachment of the cells of Pseudomonas syringae pv. atropurpurea NIAES 1309 onto the leaf surface of Italian ryegrass (Loium multiflorum Lam.) was analyzed by using two strains, wild-type strain (WT strain) and the strain containing the plasmid pBPW1:: Tn7 (pBPW1 strain), which gives the microbial cell surface a more negative charge and allows the microbes to attach more easily to inert surfaces. The leaf surface facing the ground (the dorsal side) was as hydrophobic as the Teflon membrane, whereas the surface facing the sky (the frontal side) had hydrophilicity intermediate between the Teflon and glass surface, i. e., the polar component of the surface tension of the frontal side of leaf was ca. half of that of a conventional glass slide. The cells were suspended in medium at various pHs and salt concentrations and allowed to be in contact with the leaf surfaces. In almost all medium conditions, more cells of both strains attached to the frontal side of the leaf than to the dorsal side. More pBPW1 cells attached at either surface of the leaf compared with the WT cells. Both strains showed the maximum cell attachment to the frontal side of the leaf around pH 5 to 6. The number of attached cells decreased under a high salt concentration (100mM). The pBPW1 cells attached more firmly to the leaf surface compared with WT cells, indicating a specific interaction between the cell surface and the leaf surface.