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Aims: 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.Methods: 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).Results: 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.Conclusions: Border cells can trap Pb and prevent damage to the root tip. [ABSTRACT FROM AUTHOR]

Premise of the Study: Lead (Pb) is a contaminant whose removal from soil remains a challenge. In a previous study, border cells released from root tips were found to trap Pb, alter its chemistry, and prevent root uptake. Rhodizonic acid (RA) is a forensic tool used to reveal gunshot residue, and also to detect Pb within plant tissues. Here we report preliminary observations to assess the potential application of RA in exploring the dynamics of Pb accumulation at the root tip surface. Methods and Results: Corn root tips were immersed in Pb solution, stained with RA, and observed microscopically. Pb trapping by border cells was evident within minutes. The role of extracellular DNA was revealed when addition of nucleases resulted in dispersal of RA‐stained Pb particles. Conclusions: RA is an efficient tool to monitor Pb–root interactions. Trapping by border cells may control Pb levels and chemistry at the root tip surface. Understanding how plants influence Pb distribution in soil may facilitate its remediation. [ABSTRACT FROM AUTHOR]

Background and aims: Recent studies suggest that root border cells function in defense of the root by an extracellular DNA-based trapping mechanism similar to that described in mammalian white blood cells. Genes controlling the specialized properties of border cells as they detach from the root tip therefore are of interest. Methods: mRNA differential display was used to identify Brd13, a sequence expressed in border cells but not other root tissues. RNase protection and mRNA Northern blot analyses, and reporter gene expression under the control of the Brd13 promoter in transgenic hairy roots were used to confirm localized expression. Phenotype analysis of transgenic hairy roots expressing Brd13 antisense mRNA was carried out. Results: Brd13 was expressed constitutively in border cells but not in leaves, stems, or roots without border cells. The predicted protein shares sequence similarity with flavin-binding proteins. Transgenic hairy roots expressing Brd13 antisense mRNA exhibited abnormal growth and morphology. Conclusions: We report here that altered expression of a putative flavin-binding protein in border cells resulted in altered root development. Flavin-binding proteins play key roles in development, defense, and local auxin biosynthesis. The Brd13 gene and its promoter may be useful in creating defined changes in root development and defense. [ABSTRACT FROM AUTHOR]

Root border cells separate from plant root tips and disperse into the soil environment. In most species, each root tip can produce thousands of metabolically active cells daily, with specialized patterns of gene expression. Their function has been an enduring mystery. Recent studies suggest that border cells operate in a manner similar to mammalian neutrophils: Both cell types export a complex of extracellular DNA (exDNA) and antimicrobial proteins that neutralize threats by trapping pathogens and thereby preventing invasion of host tissues. Extracellular DNases (exDNases) of pathogens promote virulence and systemic spread of the microbes. In plants, adding DNase I to root tips eliminates border cell extracellular traps and abolishes root tip resistance to infection. Mutation of genes encoding exDNase activity in plant-pathogenic bacteria ( Ralstonia solanacearum) and fungi ( Cochliobolus heterostrophus) results in reduced virulence. The study of exDNase activities in plant pathogens may yield new targets for disease control. [ABSTRACT FROM AUTHOR]