The activation of two growth-substance systems accompanying the conversion of normal to tumor cells in crown gall.

Crown gall, a neoplastic disease of plants, is of interest because the inciting bacterium, Agrobacterium tumefaciens (Smith and Town.) Conn, converts normal plant cells to tumor cells in short periods of time. Once the cellular alteration has been accomplished, the continued abnormal proliferation of the affected host cells becomes completely independent of the inciting organism. These findings indicate that a tumor-inducing principle, which is as yet uncharacterized, passes from the bacterium to the host cells and brings about a complete and profound change in the subsequent behavior of those cells. When fragments of bacteria-free crown-gall tumor tissue (but not thoroughly ground-up tumor cells) are implanted in a healthy host of the same species, the tumor tissue fragments develop into typical crown-gall tumors. An at tempt has been made in this study to characterize within the crown-gall tumor cell the metabolic systems that are primarily affected as a result of the alteration of normal plant cells to tumor cells. Uncontrolled cellular growth in crown gall appears to be ultimately concerned with the increased availability to the tumor cell of a growth-promoting substance or substances synthesized by tha t cell. A recent analysis of crown-gall tumor tissue extracts (~) has shown that two separate growth factors act synergistically to promote the rapid growth by cell division of normal tobacco pith parenchyma tissue. The first of these is an auxin and is concerned, for purposes of this discussion, with cell enlargement, while the second is concerned with cell division. Neither growth factor when used by itself is effective in stimulating division of the pith cells. Auxin, however, causes individual pith cells to enlarge greatly, as was first shown by Newcomb (4). Tobacco pith cells have apparently lost, as a result of their differentiation, the capacity to produce physiologically detectable amounts of either the cell division or the cell enlargement factor. Because both growth-substance systems appeared