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Articles

Strain-Dependent Temperature-Sensitive Phase in Crown Gall Tumorigenesis ¹

Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, Pennsylvania 19111

The effect of high temperature treatments on the early stages of crown gall tumorigenesis in sunflowers was investigated. Treatments of 32 C initiated at various times during the first ten days after infection had a similar effect on tumors induced by Agrobacterium tumefaciens strains B₆ and C58. Tumor growth was sensitive to 32 C until 60 to 72 hours after infection and was stimulated by 32 C after that time. Therefore, the "inception phase" for both C58 and B₆-induced tumors ends between 60 to 72 hours after infection. In contrast, B₆ and C58 tumors varied in their response to 37 C treatments during the first 168 hours after infection. Both C58 and B₆ tumors were sensitive to 37 C during the first 72 hours; however, B₆ tumors became resistant to 37 C after 96 hours, whereas C58-induced tumors remained sensitive until 144 to 168 hours after infection.

The growth rate of C58 and B₆ tumors in plants moved to 32 C at 90 hours after infection was the same. B₆ tumors in plants moved to 37 C at 90 hours after infection also continued to grow rapidly, whereas C58 tumors in plants moved to 37 C at 90 hours exhibited a complete cessation of tumor growth. The 37 C temperature-sensitive period specific to C58 tumors ceases by 168 hours after infection. This indicates that the temperature-sensitive functions are no longer required after 168 hours. The possible significance of this work with regard to the presence of a temperature-sensitive plasmid, pTiC58, in strain C58 and the mechanism of tumor-inducing plasmid DNA maintenance in incipient tumor cells is discussed.