VIRULENCE OF AGROBACTERIUM ON LARIX-DECIDUA AND THEIR CELLULAR INTERACTIONS AS DEPICTED BY SCANNING ELECTRON-MICROSCOPY

European larch (Larix decidua Mill.) seedlings were inoculated with a number of Agrobacterium strains to screen susceptibility to infection by agrobacteria. Nine of fourteen Agrobacterium strains tested were virulent on this conifer species. The attachment of virulent Agrobacterium to larch seedling tissues was examined using scanning electron microscopy. Electron micrographs showed the attachment specificity of virulent Agrobacterium to larch cells at wound sites in a manner similar to that described for cells of susceptible dicotyledonous angiosperms, indicating a host-parasite relationship between oncogenic Agrobacterium spp. and young seedlings of European larch. These unique electron micrographs provide the first opportunity to document the compatible interactions of Agrobacterium and a conifer at the cellular level. Further, the evaluation of tumour formation frequency suggested that the interactions between Agrobacterium and European larch were affected by wound site, position of inoculation, age of plant tissues, and time of co-culture. Successful infection of Agrobacterium resulted in genetic transformation of host cells. Agrobacterium-mediated DNA transfer and expression of bacterial genes in larch tissues were confirmed by both Southern blot analysis and opine assay with the transformed tissues.