Henry N. Wood

Variation in hormone autonomy and regenerative potential of cells transformed by strain A66 of agrobacterium tumefaciens

Mutant Agrobacterium tumefaciens strain A66 is shown to differ from its wild-type progenitor (strain A6) by a spontaneous 2.7 kb DNA insert into the T-DNA region of its Ti plasmid. Tobacco stems transformed by A66 exhibit an attenuated response characterized by slow growth and shoot proliferation. Clonal analysis demonstrates that this response is due to an alteration in the growth and regenerative potential of transformed cells, rather than to variation in the frequency of fully autonomous cells within the primary tumor. Cloned A66 transformed tobacco cells exhibit an auxin requirement for growth that can be overcome by shoot proliferation. Other host species, however, may complement the A66 mutation yielding fully auxin-independent tumors when transformed by this bacterium.

The Plant Tumor Problem

Publisher Summary This chapter focuses on the plant tumor problem. The tumor problem is a cellular problem and, at that level, no real fundamental differences exist between members of the two kingdoms. In comparing plant and animal tumors, it must be remembered that there are certain developmental and functional differences commonly used in the differentiation of animal cancers that are more or less restricted to animals and cannot be carried over and applied to plants. The first of the nonself-limiting neoplastic diseases of plants is known as Blacks wound tumor disease. The second nonself-limiting tumorous disease of plants, known as the Kostoff genetic tumors, is one in which the genetic constitution of the host and, more particularly, all of the cells comprising the host play a primary role. The third nonself-limiting tumor disease is the crown-gall disease. Tumor formation takes place in essentially two distinct phases. In the first phase, normal cells are altered to tumor cells which do not, as yet, develop into a neoplastic growth. The second phase, according to this concept, is concerned with the continued abnormal and autonomous proliferation of the tumor cells once the cellular alteration has been accomplished. The rapid and consistent response of susceptible plant cells to transformation by a tumor-inducing principle in the crown-gall disease makes possible a very accurate seriation of events that occur during tumor inception. Studies dealing specifically with the biochemistry of the inception phase of tumor formation in the crown-gall disease are very limited in number and of recent origin. The abnormal histological and cytological picture observed in the plant tumor cells can be accounted for in terms of the abnormal growth hormone physiology, which is characteristic of the tumor tissue. Findings indicate that the crown-gall tumor cell contains both genetic and nongenetic factors that are present in a normal cell.