Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 1995
Publication Date: N/A
Interpretive Summary: This paper provides a continuation of the use of a new sterile hydroponic culture system to understand the processes by which plants take up iron from the soil. Iron is an essential mineral nutrient that is required not only for proper plant growth and development, but also for human nutrition. The crops grown in many agricultural areas are affected by iron deficiencies, and the understanding of the ways that plants acquire iron, and respond to iron deficiency is essential in developing a sustained and economical means of supplying iron to plants. To address this problem, the research reported in this paper deals with the characterization of the ways plant roots take up iron. The use of the sterile hydroponic culture system allowed us to conduct the experiments without the interference of microorganisms. It was determined that the sterile-grown onion plants were unable to take up iron that was supplied as smicrobial chelates of Fe. These compounds, produced by soil microorganisms strongly influence the chemical states of iron at root surfaces. This research will further our understanding of the roles of soil microorganisms in contributing to plant nutrition.
Technical Abstract: Onion (Allium sativum) plants grown without Fe in sterile nutrient solutions readily developed chlorosis symptoms. Fe-deficiency in the sterile-grown plants stimulated the rates of root extracellular reduction of Fe3+, Cu2+, Mn4+, and other artificial electron acceptors. While rapid reduction occurred with the synthetic chelate Fe3+HEDTA, no short-term reduction occurred with the fungal siderophore Fe3+ ferrioxamine B (FeFOB) In addition to the increased rate of extracellular electron transfer at the root surfaces, the Fe-deficient plants showed greater rates of Fe uptake and translocation than the onion plants grown with Fe. The rates of uptake and translocation of Fe were sharply higher for the Fe-deficient plants supplied with FeHEDTA than for similar plants supplied with FeFOB. Inhibition by BPDS of the Fe uptake by the Fe-deficient onion plants further supported the importance of Fe3+ chelate reduction for the uptake of Fe into the roots. Rates of Fe uptake and translocation by Fe-deficien onion plants supplied with 55FeFOB were identical to the rates of uptake of ferrated [14C]-FOD; a result that gives evidence of the uptake and translocation of the intact ferrated siderophore, presumably by a mechanism not involving prior extracellular Fe3+ reduction. Differences in the rates of transport of other micronutrients into the roots of the Fe-deficient onion plants were evident by the significantly higher Zn and Mn levels in the shoots of the Fe-deficient onion.