Tumorous crown gall response to iron‐deficiency stress in sunflower

Abstract

Abstract Tumorous crown gall tissue in sunflower (Helianthus annus L.) initiates a mechanism for making Fe available to itself as evidenced by its ability to reduce Fe3+ to Fe2+. The objective of this study was to determine if a limited Fe supply to the plant might affect the growth, nutrition and reduction of Fe3+ to Fe2+ by the tumorous crown gall. Healthy green 14‐day‐old sunflower plants (cv mammoth Russian) were either stem‐inoculated with Agrobacterium tumefaciens to induce tumorous crown gall tissue development or were left uninoculated for comparison. The plants were grown in a modified Hoagland nutrient solution with treatments containing 0.0, 0.15, 0.6 and 2.0 mg Fe L‐1. The 0 mg Fe L‐1 treatment induced maximum Fe chlorosis, and consequently there was a release of hydrogen ions and of a yellow pigment by the roots, but there was no measureable release of ‘reductants’ by the roots. Iron‐deficiency stress (0 mg Fe L‐1) also resulted in reduced tumorous crown gall growth, less reduction of Fe3+ to Fe2+, and lower levels of Fe in the tumorous tissue compared to tumorous tissues adequately supplied with Fe. The tumorous crown gall tissue on the stem reduced much more Fe3+ to Fe2+ than the nontumorous stem tissue regardless of Fe level in the treatment. Tumor tissue contained more Fe, Cu and P than the nontumorous stem tissues which may indicate a modified metabolism in this tissue. An abundant supply of Fe seems to enhance the development and growth of the tumorous crown gall tissue and a deficient supply of Fe retards its growth.