Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1996
Publication Date: N/A
Interpretive Summary: Interpretive Summary not needed for this 115.
Technical Abstract: Our understanding of the whole plant and molecular processes which regulate root Fe(III) reductase activity in higher plants is incomplete; the root Fe(III) reductase has been implicated as the rate limiting process in plant Fe acquisition. Recent studies utilizing shoot:root grafts of mutant (the Fe-hyperaccumulator DGV(dgl,dgl) and normal pea plants, or main stem steam-girdling of normal reproductive-age plants, have shown that an elevated Fe(III)reductase activity is the result of a phloem-mobile signal originating from the shoot. It is thought that this signal may be a compound which has the capacity to translocate Fe in the phloem pathway. In order to identify phloem-mobile Fe chelators, white lupin plants (that readily bleed upon incision of phloem strands) were used to characterize the protein composition of phloem during reproductive growth. SDS-PAGE and MALDI-TOF-MS (matrix assisted laser desorption ionization time of flight mass spectrometry) analyses revealed changes in the phloem protein composition with development and the presence of a low molecular weight (LMW) peptide (4.3 kDa) that binds exogenous Fe. The use of 59Fe pulse-chase experiments allowed us to identify a LMW protein by native PAGE-autoradiography analysis. Research is in progress to purify and characterize this phloem Fe-binding protein by IMAC (immobilized metal affinity chromatography)and to elucidate its amino acid sequence. In addition, we will screen the Fe-hyperaccumulating pea mutant DGV (dgl,dgl) for the presence of an Fe-translocating protein/signal in the phloem. This research is being funded by USDA-ARS Cooperative Agreement No. 58-6250-1-003 and by USDA-CSRS Grant No. 94-37100-0823 to MAG.