Fine structure of sunflower crown gall tissue

Abstract

Electron microscopic examination of thin sections from sunflower crown gall tissue, induced by Agrobacterium tumefaciens, revealed certain details about its intracellular organization not previously reported. Tumor tissue showed a marked increase in the number of ribosomes, endoplasmic reticulum, and Golgi dictyosomes, over that of normal mesophyll cells. Mitochondria and chloroplasts did not show any detectable change. Crystalline bodies, consisting of a lattice surrounded by a unit membrane, were frequently observed in tumorous cells. The nucleoli of tumor cells contained vacuoles and were clearly differentiated into two zones, pars amorpha and nucleolonema. The possible significance of these ultrastructural changes has been discussed. Small vesicle-like bodies were observed in the nuclei of mesophyll cells 4 days after bacterial inoculation. Whether or not these vesicle-like bodies are responsible for the transformation of a normal mesophyll cell to a fully autonomous tumor cell is not known, but the possibility is an intriguing one.