Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/6/1999
Publication Date: N/A
Technical Abstract: Although recent studies have helped to identify a number of higher plant Zn transporter homologs, their functional significance to whole-plant Zn physiology is unclear. In order to better understand Zn nutritional physiology in higher plants, we have screened EMS-mutagenized seeds of the model legume, Medicago truncatula, and have isolated four mutants with elevated Zn requirements. Phenotypically, these mutants have normal leave initially, but after they are fully expanded, small necrotic lesions begin to appear. This is followed by chlorosis and premature leaf senescence. A normal leaf phenotype can be maintained by growing the plants hydroponically with high levels of Zn. These observations are consistent with our hypothesis that these mutants have a defect in Zn transport somewhere between root uptake and transport into leaf cells. In young sink leaves, Zn is imported both via the xylem and phloem pathways. As leaves mature and become source tissues, Zn is still imported via the xylem, but it now is exported through the phloem. If xylem transport of Zn into leaves is impaired in these mutants, then as leaves mature and begin exporting Zn, we would expect Zn deficiency symptoms to appear. We are using RT-PCR to clone Zn transporter genes in Medicago truncatula, based on sequence information for Zn transporter genes (ZIP's) from Arabidopsis. These genes will be used as probes to further understand the processes controlling Zn movement through the plant. We will discuss Zn partitioning in both mutant and wild type plants grown on various Zn regimes and will present a basic model of zinc homeostasis. This work was funded by USDA- ARS Cooperative Agreement No. 58-6250-1-003.