Trapping of lead (Pb) by corn and pea root border cells
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Most plants produce a root tip extracellular matrix that includes viable border cell populations programmed to disperse into soil. Like neutrophils, border cells export structures that trap pathogens and prevent root tip infection. Border cells also trap metals. The goal of this study was to determine if border cells trap Pb.
Border cell responses to Pb were observed microscopically. Border cell impact on Pb-induced injury to roots was assessed using root growth assays. Pb removal from solution was measured using inductively coupled plasma mass spectrometry (ICP-MS). Speciation of Pb associated with border cells was evaluated by synchrotron X-ray absorption spectroscopy (XAS).
Increased border cell trap size and number occurred within minutes in response to Pb but not silicon (Si). Transient immersion of root tips into Pb after border cells were removed resulted in growth inhibition. Immersion of root tips and border cells into Pb solution resulted in significant removal of Pb. Si levels in the presence of root tips remained unchanged. The Pb speciation, measured with Pb LIII XAS, altered when reacted with border cells, indicating that direct binding by extracellular traps occurred.
Border cells can trap Pb and prevent damage to the root tip.
KeywordsBorder cells Extracellular DNA traps Rhizosphere Root cap Rhizofiltration
Analysis of variance
Inductively coupled plasma-mass spectrometry
Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. The authors thank the reviewers of the manuscript for helpful suggestions to improve the presentation. The authors thank the College of Agriculture and Life Sciences and the Department of Soil, Water and Environmental Sciences at the University of Arizona, and the National Science Foundation (1032339) for their support of the research.
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