REDUCTION OF FERRIC IRON BY TUMOROUS CROWN GALL TISSUE IS ASSOCIATED WITH CELLS MODIFIED BY AGROBACTERIUM-TUMEFACIENS

Iron (Fe) uptake and use in plants is genetically controlled and physi ological mechanisms such as Fe reduction are induced during Fe-deficie ncy stress to make it available. Transfer of DNA into the cell genome by Agrobacterium tumefaciens alters physiological processes and causes undifferentiated growth. Tumor cells in sunflower (Helianthus annus L . cv. Mammoth Russian) show enhanced Fe reduction compared to normal s tem tissue in a manner similar to root cells in plants that are geneti cally switched on or off to manage Fe acquisition This study addresses whether alterations caused by the DNA transfer from A. tumefaciens re sult in Fe reduction or whether A. tumefaciens inoculum alone reduces Fe. Reduction of Fe was quantified from A. tumefaciens inoculum and fr om uninoculated or inoculated sunflower stem tissues daily over a 14-d ay period. Neither A. tumefaciens inoculum nor uninoculated stem tissu e alone activated massive Fe reduction. High rates of Fe reduction wer e associated with the proliferation of cells modified by A. tumefacien s. The mechanisms that transformed normal tissue to uncontrolled tumor growth appeared to be linked to active Fe reduction. These modified c ells may provide a key to locating and understanding the genetic contr ol of the Fe reduction process in plant cells. Our results suggest a c ritical role for Fe in development of tumorous tissues and raises the question of whether other tumor cells induce similar mechanisms for Fe acquisition.