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Plant root interactions with biotic and abiotic environmental stressors affect numerous aspects of human and environmental health. Plant root border cells comprise a dynamic barrier that mediates harmful effects to the plant by protecting vulnerable root tips from injury and infection and thereby facilitating plant growth and development. Recent studies have revealed that, as in animals, extracellular DNA (exDNA) trapping plays a central role in defense, but the mechanism remains poorly understood. Upon immersion in water, border cells and the associated exDNA mucilage structures rapidly disperse and are primed for function in defense of the root tip. The goal of this research was to utilize lead (Pb) as a model to examine the hypothesis that border cells function to protect plant health by utilizing exDNA-based defense mechanisms against biotic and abiotic threats. The experimental approaches were (1) to detect and study the role of exDNA in the response of border cells to pathogenic microbes; (2) to analyze the interactions of lead (Pb) with border cells; and (3) to explore the role of exDNA in Pb trapping by using various nucleases and a Pb-specific stain. The results revealed that exDNA is present in a matrix surrounding root border cells. The central role of the matrix in defense against pathogens and toxic metals was revealed by the discovery that its degradation by nuclease eliminates resistance of the root tip to infection and injury. Border cell exDNA traps immobilized phytopathogenic bacteria Ralstonia solanacearum, which were then dispersed upon treatment with a nuclease. This indicates that the trapping mechanism is exDNA-based and an important defense function of border cells. To test its role in defense against abiotic stressors, we investigated the interactions of border cells and Pb. The ability of border cells to remove large amounts of Pb from solution was demonstrated by ICP-MS analysis. Up to 20% of the Pb in a 1 mM solution was removed by the bo

Controlled environment agriculture offers a solution to challenges including less available land, water deficits, and consumer demand for pesticide free produce. However, control of soil-borne diseases is a major limiting factor. The goal of this dissertation was to examine predictions of the hypothesis that border cells function to protect plant health by controlling microorganisms associated with plants grown in hydroponic culture. Border cells separate from root tips upon immersion in water, and appear to have important roles in the defense mechanisms of plant roots. The general objectives were (1) to study the delivery of border cells in hydroponics; (2) to evaluate interactions between border cells and microorganisms in hydroponics; and (3) to explore approaches to alter border cell production for improved root disease control. In this study it was confirmed that border cells can be released continuously into the solution of hydroponic culture suggesting that plants grown in this system may use extra energy in the production of new border cells. Free border cells interacted with microorganisms present in the hydroponic solution by secreting an extracellular capsule. Previous studies showed that proteins are a key component of this capsule, including lectins. The interaction of pea lectin and Nectria haematococca spores therefore was explored. Results demonstrated that pea lectin agglutinates fungal spores in a hapten-specific manner, and inhibits their germination. Lectin had no negative effect on root development suggesting that it could be used as a potential control for soil-borne diseases in hydroponics. To control the production of border cells, subsequent studies measured the impact of a transient exposure of root tips to different metabolites secreted by root caps and border cells. Exposure to specific metabolites altered the production of border cells without measurable effects on root growth and development. This is in contrast to results obtained with