Title: What we understand about micronutrient minerals in plants – with relevance to biofortification strategies Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 10, 2010
Publication Date: November 9, 2010
Citation: Grusak, M.A. 2010. What we understand about micronutrient minerals in plants – with relevance to biofortification strategies[abstract]. First Global Conference on Biofortification, November 9-11, 2010, Washington, DC. Available: http://www.box.net/shared/bllfietklq. Technical Abstract: Essential microelements such as iron and zinc are required throughout plant growth. They are needed both to support metabolic processes in vegetative tissues, and for eventual deposition in seeds – the latter to provide mineral nourishment for the seedling plant at the start of the next generation. This deposition also determines the nutritional quality of seeds as a source of dietary nutrients for humans; therefore, scientists in the biofortification arena have been interested in understanding how these microelements are transported into and throughout each plant species under normal conditions, how these transport processes could be manipulated to enhance micronutrient density, and in what form these elements are stored in plant tissues. Because iron and zinc can be toxic to the plant when acquired in excess amounts, their absorption at the root-soil interface and subsequent transport throughout the plant must be carefully regulated to maintain adequate, but non-toxic levels. Thus, plants have developed a cadre of membrane transporters for metal ions (and/or for metal chelates) that are coordinately utilized to traffic metal ions into the roots, on into the water-conducting xylem pathway for delivery to the shoots, and eventually to the sugar-conducting phloem pathway for delivery to various sink tissues, such as developing seeds. Along the way, plants use some of these same transporters (along with other mechanisms) to store and partition iron and zinc in ways that make these elements both readily available, but also non-damaging, to the plant. In this presentation, the various molecular mechanisms that have been identified to move metal ions across membranes and on into different sub-cellular compartments, will be discussed with respect to their role in moving iron and zinc up to and along the long-distance transport pathways. Specifically, we will describe how these transporters are arranged spatially and temporally to effectively move metals throughout the whole-plant continuum. We will discuss how shoot-to-root communication via the phloem pathway, regulates root iron acquisition processes (and possibly the transport/uptake mechanisms of other metals). Furthermore, recent evidence for the involvement of transcription factors in the regulation of metal mobilization from source leaves to developing seeds (via the phloem pathway) will be presented. Finally, we will discuss some of the efforts that have been undertaken to manipulate the plant's complex transport machinery, with the goal of increasing the levels of iron and/or zinc in seed crops. We will discuss why some of these efforts have, or have not, been successful. Because of the multi-compartment, multi-process complexity of whole-plant metal transport, it is clear that effective strategies to manipulate micronutrient levels in seeds (a terminal compartment in the plant) will not be easy. A deep and thorough understanding of all component mechanisms is required, as well as an understanding of which processes impose a rate-limitation to the overall system. It is hoped that this presentation will provide the audience with an appreciation for how far we have come in our knowledge on this topic, but also an awareness of the challenges, opportunities, and critical need for further research in this area.