The Etiology of Crown-Gall

Abstract

The syndrome crown-gall is a complex which includes diverse behaviors of many species of plants in the presence of different strains of bacteria. The behavior is predicated on the proposition that each event or process arises from a causal complex of which each component is a necessary but not a sufficient cause of the event or process under consideration. In so far as the event is not spontaneous, it is a change or effect produced by an affector. Four stages are recognized in the genesis of grown-gall: (1) primary transformation period; (2) duplication; (3) organization and differentia-tion; (4) senescence and necrotony. Events of the conditioning phase are wounding of the prospective tumorous tissues and their responses to the products of wounded cells. Crown-gall bacteria do not seem to be necessary for any of these processes. Wound substances, possibly auxins released from, or formed by ruptured cells, predispose them to subsequent events. Conditioning determines the potential range of response of the cell. In the induction phase the main etiological agent which is active seems to be the metabolic product of the bacteria. This agent, "tumor-inducing principle", is synthesized by those strains of bacteria which possess or have acquired the proper constitution. The principle may be a special polymer of DNA, synthesized only in the presence of wound sap. Incipient tumor cells are not characterized by any special histological or cytological modification. Secondary tumors resulting in the transformation period do not appear to require wound substance, nor the presence of bacteria in intimate contact with the cells. In the 3d period, cellular differentiation and organization of cells into tissues and a structurally complex tumor may occur. The tumor then consists of a peripheral region, regions of duplicating cells, and regions of cell differentiation. Necrobiosis and necrosis are the dominant cellular and tissue events of the senescence and death stage of the life history.