ARS | Publication request: A GENETIC MUTATION THAT REDUCES CALCIUM OXALATE CONTENT INCREASES CALCIUM AVAILABILITY IN MEDICAGO TRUNCATULA

Submitted to: Functional Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2006
Publication Date: July 1, 2006
Citation: Nakata, P.A., McConn, M.M. 2006. A genetic mutation that reduces calcium oxalate content increases calcium availability in Medicago truncatula. Functional Plant Biology. 33:703-706.

Interpretive Summary: Oxalate is an antinutrient that locks calcium up in the form of a calcium oxalate crystal. Calcium found in this crystalline form in foods can not easily be absorbed. To determine the feasibility of improving the absorbability of calcium from plant foods we tested calcium availability in near isogenic plants that differ only in their ability to store calcium in the crystalline form. This test included the use of an in vitro system that simulated the digestive process. In brief, the leaves from the two different plants were ground up to simulate the chewing process. The ground material then was subjected to a variety of digestive juices in a sequential order to mimic the processes that occur in the gut and intestines. The minerals that were released from the plant material were then measured. The authors found that the leaves from the plant lacking crystals released more calcium than the plant containing the crystals (other minerals amounts were found to be the same). Such a finding shows for the first time the feasibility of improving the calcium availability in plant foods through genetic manipulation of its oxalate content. The study emphasizes the point that it is not just how much of a particular nutrient that you ingest in your diet that is important, but also the form of that nutrient. It is the form of the nutrient that governs its bioavailability, meaning how much you will be able to absorb and utilize.

Technical Abstract: Oxalate is considered an antinutrient that renders calcium unavailable for nutritional absorption by humans. Efforts have been made to generate and identify edible plants with decreased levels of this antinutrient. The extent to which a food can be nutritionally improved through genetic alterations in calcium oxalate content, however, has not been determined. The recent identification of near isogenic lines of the forage legume, Medicago truncatula Gaertn. (cv. Jemalong genotype A17), that differ in calcium oxalate content aids in filling this gap in our knowledge. In this study, we used an in vitro dialysis system to show that the decrease in calcium oxalate results in an enhancement in calcium availability. By comparing virtually identical plants a more direct assignment of the calcium availability to the presence or absence of oxalate was made. In addition, this study shows, for the first time, the feasibility of improving plant foods through the genetic manipulation of its oxalate content.