THE INTERACTION OF NORMAL AND CROWN‐GALL TUMOR TISSUE IN IN VITRO GRAFTS

Abstract

IN A PREVIOUS paper (de Ropp, 1947a), an account was given of tumors which appeared to arise from normal tissue of Helianthus annuus to which bacteria-free crown-gall tissue had been grafted in vitro. These outgrowths possessed a characteristic structure which distinguished them from the tumor tissue that had induced their formation. The fact that one of them arose at a site remote from the point of union of the tumor scion, suggested that these tumors might have been induced in the normal stem tissue by the agency of a virus-like factor capable of being transmitted from tumor to normal tissue by grafting. The experiments to be described in this paper were designed to throw further light on the mechanism of development of these induced tumors. MATERIALS AND METHODS.-Five different strains of crown-gall tumor tissue were used to provide the tumor scions in these experiments. Their origins and characteristics are described below: (1) Strain H13. Isolated from a secondary tumor on sunflower in 1941 (White and Braun, 1942). A white rather slowly growing strain of tumor tissue having a firm consistency. (2) Strains Pi and PlII. Isolated from primary tumors on sunflower in 1946 (de Ropp, 1947b). 1 Received for publication January 30, 1948. This research was supported in part bv the Committee on Growth of the National Research Council Acting for the American Cancer Society. The writer is indebted to Miss E. Pieczur for technical assistance in connection with this work. Both very soft and structureless strains of tumor tissue with rapid rates of growth. (3) Strain PII. Isolated from a primary tumor on sunflower in 1946 (de Ropp, 1947b). A very woody strain with a tendency to grow below the surface of the agar and an unusual capacitv for continued growth without subdivision. (4) Strain KI. Isolated from an induced tumor on an in vitro graft in 1946 (de Ropp, 1947a). Initially, this strain grew in the form of small spheres each having a woody core and a soft cortex. Later, this characteristic disappeared and the strain became soft and structureless. The normal sunflower tissue to which the grafts were made was obtained from the first internode of 4-week old plants which had been rendered sterile by the removal of the epidermis. The internodes were cut into 4 or 9 mm. segments. Tumor tissue was placed either on the physiological top or the physiological base of these segments and supplied with nutrients from the agar until union had taken place. The nutrient used has already been described (White and Braun, 1942). The material was grown in an incubator at 25?C. in continuous light. For histological examinations, material was fixed in Navashins solution, embedded in paraffin wax and sections stained in safranin and Heidenhain's haematoxylin. EXPERIMENTAL. Frequency of formation of induced tumors.-All five of the tumor strains described above were used in this experiment. Seg-