Calcium oxalate content affects the nutritional availability of calcium from Medicago truncatula leaves

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.