CONTACT BETWEEN ROOT AND IRON SUBSTRATE AND THE MOBILIZATION OF IRON BY SOYBEAN ROOTS

The question of whether a direct (uninterrupted) contact between plant roots and solid substrate is a prerequisite for the mobilization of s paringly soluble iron (Fe) by plant roots was investigated. Factorial combinations of two types of contact between the roots and rooting med ium [direct or interrupted (roots placed inside a dialysis tube (DT)], two rooting media (nutrient solution or vermiculite), and two Fe supp ly conditions [without soluble Fe (control) or plus Fe-EDDHA] were inv estigated. Placing the roots inside DT, with no visible mechanical imp edance for the root, reduced the growth of tops and roots in most case s. Iron mobilization, judged by the total amount of Fe in the tops, st rongly decreased if roots were enclosed in DT. This was true in plants grown in vermiculite as well as in nutrient solution containing Fe-FD DHA. It is concluded that a direct contact between the surface of root cell walls and the Fe substrate is a prerequisite for the Fe mobiliza tion by the plant roots.