Submitted to: Texas Experiment Station Field Day Handout
Publication Type: Experiment Station
Publication Acceptance Date: 6/2/2010
Publication Date: 6/29/2010
Citation: Pinson, S.R., Tarpley, L., Ratnaprabha, Salt, D., Guerinot, M.L. 2010. Found: Rice that produces grains with improved nutritional value. Texas Experiment Station Field Day Handout. VII - VIII; http://beaumont.tamu.edu/eLibrary/Newsletter/2010_Highlights_in_Research.pdf. Interpretive Summary:
Technical Abstract: Rice provides the major source of nutrition for a large proportion of the world’s population, and is a key ingredient in baby foods in the U.S. Mineral nutrients such as Ca, Fe, and Zn play critical roles in human health, with over 3 billion people suffering from Fe and Zn deficiencies. Unfortunately for those who rely on rice for subsistence, rice grain is not a concentrated source of these nutrients, and if grown on contaminated soils, can contain toxic elements such as As and Cd. Drs. Pinson and Tarpley recently identified rice lines exhibiting significant improvements in the content of 16 elements, namely Mg, P, K, S, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, and Cd, and are now investigating the genes and physiology underlying their improved nutritional value. Research Methods: The USDA maintains a repository of seed collected from wild and cultivated rice lines found all around the world. A core subset of 1700 accessions from among the 17,000+ rice accessions in the USDA National Small Grains Collection was selected to represent the wide genetic diversity contained within the larger set of rice. Before these lines could be compared for nutritional value, they had to first be grown side-by-side under controlled field conditions. It is well known that the amount of oxygen in the soil greatly affects the availability of soil nutrients. Therefore we grew the 1700 foreign rices under both flooded, and unflooded conditions, two replications per year, in both 2007 and 2008 at the Beaumont rice research station. Seed was harvested, dried, threshed, and hulled, then sent to a collaborator at Purdue University who analyzed them for accumulation of Mg, P, K, S, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, and Cd. To minimize the effect of variable soil, the rice lines were grown closely together in the field, with 5 seed drill-seeded into hillplots. Fifteen repeated check-plots paired with fifteen soil samples per replication were grown/collected in a grid pattern. This allowed us to document that the impact of environmental variance within each paddy was small compared with genetic impact on grain element content. Large (> 5x) ranges in grain content were found for each of the 16 elements, with the unflooded field treatment showing more extreme differences in grain nutritional value than the flooded rice. Rice accessions high for a particular element were sometimes found to have similar geographic origins. For example, four of the five lines highest in Mo content originated from Malaysia. The common origin of the high-Mo accessions is exciting in that it verifies that we have found lines with key genes allowing them to accumulate high levels of Mo in their grains. The fact that these Malaysian rices were collected on three different trips spanning two decades suggests that the Mo-genes are easily passed from one generation to the next, and appear to be beneficial rather than detrimental to rice yields and health or they would not have been maintained over decades of breeding. Future research: Studies to identify the genes and the physiological attributes underlying the improved grain mineral contents are underway. We will be asking if their increase mineral content is due to increased root uptake, increased transport through the plant, or a combination of the two. Spatial location of the accumulated minerals within the rice kernel is also under investigation. It will be easier to impact human diets if the minerals are accumulated in the endosperm rather than in the embryo or bran layer which are not ingested unless one is eating brown rice.