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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]

Here we describe the use of Pisum sativum L. as a model system to measure how short-term treatment of root tips with soluble metabolites can influence root growth and release of root exudates. The results revealed that even a 3-minute exposure of root tips to metabolites normally released from roots into the rhizosphere (e.g. rhamnose, ferulic acid, salicylic acid) can significantly influence root growth without affecting production of border cells and associated exudates. Conversely, products including caffeine, saccharide lactone, and pisatin alter production of border cells, without affecting root growth. Understanding how root-derived and exogenous metabolites can selectively impact root function may yield benefits in crop production, especially in greenhouse agriculture systems where growing roots can be exposed to a significant accumulation of plant exudates. [ABSTRACT FROM AUTHOR]