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United States Department of Agriculture

Agricultural Research Service

Title: Phloem Iron Transport from Vegetative Tissues to Developing Seeds in Pea

Authors
item Stephens, Brian - BAYLOR COLL OF MEDICINE
item Marentes, Eduardo - BAYLOR COLL OF MEDICINE
item Grusak, Michael

Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 1997
Publication Date: N/A

Interpretive Summary: Interpretive Summary not needed for this 115.

Technical Abstract: The mechanism by which Fe and other metals are phloem transported throughout the plant has significance to both the use of plants as phytoremediation tools and to the nutritional quality of edible seeds, thus, we have worked to identify the form of Fe in the phloem pathway. Previous studies using pea have indicated that Fe is phloem loaded and subsequently transported as a chelate complex. We have attempted to identify the chelator directly from phloem sap, but due to difficulties in obtaining significant quantities of this fluid, we have focused instead on isolating the chelator from pea seed coats. Seed coats were chosen because they are the terminal sink in the phloem delivery of Fe from vegetative tissues. Phloem Fe transport was studied using three pea genotypes: the wild-type 'Sparkle' and two mutants, dgl and brz. Both of these mutants can hyperaccumulate Fe in vegetative tissues, but only the dgl mutant transports excess Fe to its developing seeds. Pod-bearing nodal units wer labeled with 59-Fe and proteins were extracted from seed coats. Proteins were separated using native PAGE or gel exclusion chromatography; peptide-bound Fe was monitored using autoradiography or gamma counting. We currently are using immobilized metal affinity chromatography to isolate and purify Fe-binding peptides in order to obtain amino acid sequence information. Columns bearing immobilized ferrous iron, nickel, or copper have been utilized; the usefulness of different metal columns will be discussed. The endogenous Fe-chelator transported in the phloem of wild-type pea appears to be a peptide of less than 4 kDa. This research has been funded by USDA-ARS Cooperative Agreement No. 58-6250-1-003 and by USDA-CSRS Grant No. 94-37100-0823 to MAG.

Last Modified: 8/29/2014
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