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United States Department of Agriculture

Agricultural Research Service

Title: Direct Measurement of 59fe-Labeled Fe2+ Influx in Roots of Pisum Sativum Using a Chelator Buffer System to Control Free Fe2+ in Solution

item Grusak, Michael
item Norvell, Wendell
item Chaney, Rufus
item Kochian, Leon

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 20, 1995
Publication Date: N/A

Interpretive Summary: Iron (Fe) is an essential nutrient for both plants and humans, and iron deficiency is a worldwide problem for both. Acquiring sufficient iron from alkaline soils is difficult in plants; hence not enough iron is available in plant foods to satisfy an adult human s nutritional requirements when eaten in normal amounts. Thus, we are working to increase our understanding gof the processes plants use to acquire Fe from the soil in order to improv the Fe content of plant foods. In this paper, we developed new techniques that allow us to use radioactive Fe in solution to directly study the transport of the form of Fe normally absorbed by roots of many plant species, Fe2+. Using these new methods, we found that Fe2+ is rapidly transported into root cells in a metabolically controlled and concentration-dependent manner. We also found that if plants became Fe deficient, the Fe2+ transport system was stimulated. This new information gives us a more complete understanding of how plants acquire Fe from the soil environment, which in turn might enable us to modify the Fe transport systems in plants to increase the Fe concentrations in edible plant parts.

Technical Abstract: Ferrous transport in plants has been difficult to quantify because of the inability to control Fe2+ activity in aerated solutions, and nonspecific binding of Fe to cell walls. In this study, a Fe(II)-ferrozine3 buffer system was used to control free Fe2+ in uptake solutions. Additionally, desorption methodologies were developed to adequately remove nonspecifically bound iron from the root apoplasm. This enabled us to quantify unidirectional ferrous influx via radiotracer (59Fe) uptake in roots of Pisum sativum cv Sparkle, and its single gene mutant brz, an iron hyperaccumulator. Iron influx into roots was dramatically inhibited by low temperature, indicating that the measured iron accumulation in these roots was due to true influx across the plasma membrane rather than nonspecific binding to the root apoplasm. Both Fe2+ influx and Fe translocation to the shoots were stimulated by Fe deficiency in Sparkle. Additionally, brz, a mutant that constitutively exhibits high ferric reductase activity, exhibited higher Fe2+ influx rates than +Fe grown Sparkle. These results suggest that either Fe deficiency triggers the induction of the Fe2+ transporter, or that the enhanced ferric reductase activity somehow stimulates the activity of existing Fe2+ transport protein.

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