Iron (Fe2+)-induced toxicity produces morphological and physiological changes in roots inPanax ginsenggrown in hydroponics

Rusty roots markedly influence on ginseng cultivation, and this phenomenon often attributed to iron (Fe) induced toxicity. To examine the physiological mechanisms underlying Fe-initiated toxicity as evidenced by rusty roots in Panax ginseng, morphological and physiological changes in roots were investigated in hydroponics using Fe2+ concentrations of 50 (control), 100, 200, 400 or 600 µM. Compared with control, reddish-brown deposition at the root surface increasingly appeared as Fe2+ concentration increased (≥200 µM). The pH also rose as Fe levels were elevated. Higher external Fe2+ concentrations produced changes in root organelles and cell structures. Structural alterations in mitochondria due to excess Fe storage, protoplast shrinkage and cell vacuolation as well as formation of central vacuole with deposits in roots were observed. In addition, apparent cell wall thickening, cell wall folding and shrinkage, damage of cell membranes and a large amount of cell debris occurred at higher external Fe2+ concentrations (≥400 µM). The Fe2+ mediated damage resulting in morphological and physiological changes in ginseng roots was concentration and pH dependent.