Interactions of Wild-Type and a Cellulose-Minus Mutant ofAgrobacterium tumefacienswith Tobacco Mesophyll and Tobacco Tissue Culture Cells

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Abstract
The interactions of A. tumefaciens wild-type strain A6 and A. tumefaciens strain Ce-12, a cellulose-minus transposon mutant of A6, with tobacco mesophyll cells, tobacco suspension culture cells, and tobacco callus cells were examined by using scanning electron microscopy. Bacteria of both strains were seen in association with tobacco cell walls of all 3 cell types within 90 min of inoculation. Cells of A. tumefaciens strain A6 synthesized cellulose fibrils during their attachment to tobacco suspension culture cells. Such fibrils served to entrap nonattached agrobacteria and resulted in the formation of large clumps of bacteria attached to the tobacco cell surface. A lesser, but still substantial, number of fibrils was formed by A. tumefaciens which were associated with tobacco callus cells. A more modest number of fibrils was formed by bacteria associated with tobacco mesophyll cells. Exposure to increasingly wet environments resulted in increased fibril formation by A. tumefaciens wild-type strain A6. No fibrils were formed by, or in response to cells of A. tumefaciens strain Ce-12 even 17.5 h after inoculation. This indicates that all fibrils formed were probably of bacterial origin.