Uptake by plants of iron from iron chelates

Abstract

Several studies have been conducted with BPDS as a trapping agent of Fe²⁺ to prevent iron uptake by plants. The BPDS does inhibit iron uptake although the BPDS chelated iron is available to plants particularly at low solution pH. Such results, however, do not prove obligatory reduction of Fe³⁺ chelates before absorption of iron even though reduction is probably part of the uptake process. Computer derived curves (from the literature) for availability of Fe²⁺ associated with iron uptake in the presence of chelating agents imply that the first step of iron uptake is a root binding of the Fe³⁺ chelate. Reduction, splitting of the Fe from chelate and possible, but not obligatory, expulsion of the chelate from the root can follow. A hundred μmolar excess of DTPA chelating agent often enhances uptake of iron by plants even though the simultaneously available level of unchelated Fe²⁺ can be below 10^‐9.2 M, a level postulated by other workers as being too low for any uptake of iron in the Fe²⁺ form. It was assumed that any uptake under these conditions would be as chelated iron. In our studies iron uptake was increased at the 100 μmolar excess DTPA and, if only Fe²⁺ were available, iron uptake should have been essentially stopped.

Key words:

• Redox
• chelate splitting
• BPDS