Root excretions in iron-deficient tobacco plants and possible effects on iron nutrition

Tobacco plants grown without iron tended to excrete riboflavin to the external solution and to reabsorb it. The riboflavin translocation was somehow related to iron translocation in plants. Iron-deficient plants generally absorbed much more /sup 59/Fe from the chelating agent EDDHA and transported more of it to shoots than plants which were adequately supplied with iron. Nitrogen-deficiency destroyed the ability of plants to do this and their ability to produce riboflavin. Iron-deficient plants removed iron from EDDHA and left the chelating agent in the external solution. Iron-sufficient plants generally absorbed the iron chelate molecule. Iron-deficient plants resulted in H/sup +/ release to the external solution evidently as a result of a differential shift in uptake of cations such as /sup 45/Ca, /sup 85/Sr, /sup 86/Rb and /sup 137/Cs compared with uptake of /sup 82/Br as a test anion. Mild iron-deficiency generally increased cation uptake and decreased anion uptake. Withholding iron decreased salt transport to the exudate of detopped plants and negated the enhancing effect which nitrate has on exudation. Tobacco plants in an erratic manner suddenly removed all the iron from a nutrient solution and a microbial-produced organic agent other than riboflavin appeared to be involved. It had the samemore » effect as iron-deficiency on iron uptake and translocation. It is postulated that root excretions play an important role in the ability of plants to obtain at least iron from the external environment.« less