Understanding why some plants like spinach store much of their calcium in a crystalline form could help scientists develop more nutritious varieties of vegetables, reports the Functional Food Newswire.
One cup of cooked spinach contains plenty of calcium - around 244 milligrams - but most of that is in calcium oxalate crystals that humans cannot absorb so intake of calcium from spinach is just 12 milligrams, or 5%. Turnip greens, on the other hand, are nearly crystal-free, making them an excellent source of calcium. One cup of cooked turnip greens provides about as much calcium as a cup of cow's milk.
To unlock the mystery of crystal formation and function, a molecular biologist from the Agricultural Research Service (ARS), the research arm of the US Department of Agriculture, is studying a small, fast-growing plant called Medicago truncatula.
His lab has inspected thousands of genetic variations of this simple plant, which normally stores much of its calcium in crystals. While the genetic variants look nearly identical to the naked eye, some have leaf cells packed with calcium oxalate crystals while others are nearly crystal-free, the researchers reported in Plant Physiology, 2000 (vol. 124, pp. 1097-1104).
They hope to determine whether calcium oxalate crystals play an important role in helping plants adapt to stressful growing conditions or fend off attacks by pathogens and insects, and they are looking for the genes that control crystal formation.
Since the plants that don't make crystals appear to thrive as well as those that do, the researchers should be able to breed out or remove this characteristic from M. truncatula. If successful, this would be a first step toward making calcium oxalate-rich vegetables like spinach a better source of calcium for humans.