Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2007
Publication Date: 7/1/2007
Citation: Nakata, P.A., McConn, M.M. 2007. Calcium oxalate content affects the nutritional availability of calcium from Medicago truncatula leaves. Plant Science. 172(5):958-961. Interpretive Summary: Efforts to understand the link between dietary calcium and health-related conditions such as osteoporosis, cancer, and renal stone formation has brought attention to the importance of understanding calcium availability (the amount of calcium available for nutritional absorption) in foods. Calcium present in plant foods exists primarily as a complex in which it is bound to substances such as oxalate, phytate, fiber, fatty acid, protein, and/or other anions. The substance to which calcium is bound can have a dramatic influence on its availability. Substances such as oxalate and phytate bind calcium in a manner that reduces its availability. Thus, efforts have been made to determine if we can engineer plants to remove such substances to improve the nutritional value of plant foods. In a previous study we engineered plants to contain low or high amounts of oxalate. In this study we tested whether these engineered plants have improve calcium availability. Using an in vitro system that simulates the process of digestion and absorption, we determined that the plants engineered to have low oxalate have improved calcium availability and that the plants engineered to have high oxalate have decreased calcium availability. This study shows that engineering plants to improve calcium availability through manipulation of its oxalate content is a viable strategy.
Technical Abstract: It is known that oxalate, present in edible plants, can bind calcium in a crystalline form that reduces the availability of the bound calcium for nutritional absorption by humans. It is unknown, however, the degree to which the calcium oxalate content of a plant can be genetically altered and how much such alterations can impact the nutritional availability of the calcium present in plant foods. The recent identification of near isogenic Medicago truncatula mutants that contain a varying range in calcium oxalate content allows us to begin to address this gap in our knowledge. Here we assess, using an in vitro dialysis system that simulates the processes of digestion and absorption, the availability of calcium present in the leaves of M. truncatula. The results showed that calcium availability generally correlates inversely with the amount of calcium sequestered in the oxalate crystal. The plants with more calcium oxalate were found to have reduced calcium availability, while the plant with less calcium oxalate was found to have enhanced calcium availability, compared to controls. Overall, this study supports genetically manipulating the form of calcium in edible plants as a viable strategy to improve the nutritional quality.