Uncovering The Mechanisms Controlling Metal Micronutrient Homeostasis In Plants

Download or read book Uncovering the Mechanisms Controlling Metal Micronutrient Homeostasis in Plants written by Amanda L. Socha and published by . This book was released on 2016 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the human population increases, it is imperative that we develop strategies to improve agricultural productivity to meet the growing demand for food, fuel and fiber. More than 2 billion people suffer from “hidden hunger” (a lack of essential nutrients). Such micronutrient deficiencies are most common in developing countries where diets are primarily plant-based. Iron (Fe), one of the essential micronutrients, plays vital roles in both human and plant health. In plants, it is required for essential cellular processes such as photosynthesis and respiration. However, in excess, Fe can spontaneously produce reactive oxygen species (ROS) via the Fenton reaction. Fe-mediated production of reactive oxygen species (ROS) can be harmful to plant tissues, but is part of the defensive strategy against microbes. This thesis focuses on understanding 1) the role of Fe in the formation of ROS for defense against abiotic stress and 2) how Fe, Mn and Zn are loaded into the developing seed and mobilized following germination. Pretreatment of the model plant Arabidopsis thaliana with Fe significantly enhances plants defense to the bacterial pathogen Pseudomonas syringae PtoDC3000. Conversely, chelating soil iron is detrimental to plant defense. A previously uncharacterized Fe-regulated gene, Induced Systemic Resistance 2 (ISR2), negatively regulates the Fe-mediated ROS formation for defense against Pto DC3000 resulting in enhanced resistance in the loss of function mutants and increased susceptibility in overexpression lines. Furthermore, to better understand how essential nutrients are loaded into seeds, Synchrotron X-Ray Fluorescence was employed to image Fe, Zn and Mn in developing and germinating seeds. Zn and Mn are broadly distributed throughout the outer integument cells of the developing seed coat. In contrast, the majority of Fe is localized to the endosperm and to the vascular bundle cells in the embryo, indicating that the Fe pattern is set up early during development. The Zn and Mn gradients in the seed proper occurs much later in seed development, during the late bent cotyledon stage of development when Mn can now be seen to localize to a single layer of spongy mesophyll cells. After germination, Fe and Mn are found in the palisade mesophyll cells between 32-56 hours after imbibition. The mobilization of Fe and Mn is dependent on the Fe and Mn vacuolar exporters NRAMP3 and NRAMP4. Overall, this work has contributed to our knowledge of the role of Fe in plant defense and identified a key player in the basal plant defense response. In addition, our work characterizing metal phenotypes of developing and germinating seeds has improved our understanding of the path that metals take so that they are properly stored and accessed in the seed.