Cytological Studies on Agrobacterium tumefaciens : 1. Growth and Ultrastructures of the Cell

Morphological characteristics of microcolony and free cell of Agrobacterium tumefaciens, oncogenic strain At 2, were investigated by electron microscopy, in relation to growing direction of the cell body. Results obtained were summarized as follows : 1. A four-cell microcolony, which was derived from a single mother cell after two division cycles, formed the cell arrangement of parallel pairs. 2. One end (cell end B) of the growing cell was more obtusely hemispheric than the other end (cell end A) of the cell, and became to show the same morphology as the latter after initiation of cell division. These observations suggested that the cell end A was the original end of the mother cell and the cell end B was newly formed by cell division. 3. A small constriction (point G) of the cylinder was found in the growing cell. Distance from the point G to the cell end A was nearly constant regardless of the length of whole cell. On the other hand a high level of positive correlation existed between length of whole cell and distance from the point G to the cell end B. and the regression coefficient showed the value near 1.0. This result proved that A. tumefaciens At 2 cell usually grew unidirectionally at the cell end newly formed by division.