Physiology and toxicology of ion fluxes in plant roots

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My laboratory is dedicated to the exploration of transport systems in plants, and the relationship between transport pathways and plant productivity. My many discoveries in this area have proven to be of fundamental interest to a broad scientific community, having been published in Nature, PNAS, and Trends in Plant Science, and garnered over 4300 citations. I have also dedicated my work to the greater public, through public lectures, news media and personal outreach, and especially through my involvement with such groups as the International Rice Research Institute, and my own initiative, the Canadian Centre for World Hunger Research. These activities and accomplishments, among many others, have been made possible by the core operating funds consistently provided to my research program by NSERC. The research proposed here will advance our knowledge of root ion transport, mineral acquisition and toxicity, and plant growth, in the Arabidopsis model plant and in agriculturally important cereal grasses. Discovery will focus on the transport physiology of potassium (K+), sodium (Na+), and ammonium/ammonia (NH4+/NH3), with emphasis on their relation to growth, and their interactions with each other, and with water and other soil ions. While this is fundamental science, innovation in my research area has great potential for improvements in plant productivity. Of these soil components, K+ is the best studied, but new frontiers await discovery in the area of plant-K+ relations. We will examine the full complement of K+ transporters, in particular those operating when the main systems are compromised genetically and/or physiologically. We will also explore the poorly understood mechanisms underlying the interactions between K+ nutrition and NH4+/NH3 and Na+ stresses, and we will investigate the fundamental links between K+ nutrition and plant water use, especially in the context of aquaporin (water channel) activity. Discoveries in this area will help address the massive water footprint of agriculture, particularly in rice, the world's thirstiest crop. My laboratory has long specialized in plant-nitrogen relations, particularly nutritional and toxicological aspects of NH4+/NH3 provision. We have recently demonstrated that NH3 is the main permeating form of the conjugate pair under toxicity, and that its transport into plant cells is likely mediated by aquaporins. NH4+/NH3 toxicity may thus be directly tied to water flow, suggesting a new mechanism for its alleviation by K+. We are now at a critical juncture of finding the fundamental nature of this toxicity, in relation to the primary transport of NH3, and its dependence on the presence of other nutrients and stresses. My group has also recently made substantial progress in the area of sodium transport and toxicity, fundamentally revising the mechanistic model describing this important phenomenon. Many aspects of Na+ transport are still poorly understood, as are the exact mechanisms of Na+ toxicity. How much Na+ enters cells, and how much accumulates outside? Does Na+ target cell expansion, division, or disintegration? Can cellular Na+ accumulation be beneficial, even under toxicity? Can Na+ toxicity be ameliorated by reducing solute flow through the root apoplast? In addition to pursuing discovery in these critical areas, I propose to develop a leading-edge program in the epigenetics of plant nutrition, about which virtually nothing is known. I will ask how the rearing of plants influences the water and nutrient use of their descendants, and how such inheritance patterns manifest at a molecular level. How does such nutritional prehistory affect plant resistance to mineral toxicities, and can this approach be beneficial to out-planting strategies in nutrient-poor or saline soils?