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Genetic Screening for Calcium Oxalate Crystals in Plants

By Jesús García
July 28, 2000

Calcium, the fifth most abundant element in the Earth’s crust, is critical to the proper functioning of the human body. Without the one percent of calcium that is not contained in bones and teeth, blood wouldn’t clot, nerves wouldn’t fire, and muscles wouldn’t contract. Could plants serve as another source of dietary calcium for consumers?

Agricultural Research Service scientists know that calcium, in the form of oxalate crystals, accumulates within a variety of plants. What they don’t quite know yet is how to make this calcium readily absorbable by humans. Deciphering the mechanisms that regulate oxalate crystal formation may provide clues to making this nutrient more biologically available and reduce the risk associated with oxalate, which is thought to contribute to kidney stone formation.

To help identify these mechanisms, ARS researchers with the Children’s Nutrition Research Center at Baylor College of Medicine in Texas have initiated the first genetic screening system that can examine calcium crystal formation in plants. The scientists used the system to screen leaves from Medicago truncatula--a plant similar to alfalfa--that had been chemically altered so researchers could study their crystal structure.

The scientists then compared the crystal formations in these plants with crystals in control plants. They identified differences within seven different types, or classes, of mutants in terms of the plants’ crystallization process, crystal form, distribution and/or amount.

Plants in one class that contain no crystals showed no difference in their growth when compared to controls. This finding seems to refute the hypothesis that calcium oxalate crystals work to support plant tissue structure in the plant under study.

Researchers are also using the screening system to ascertain the genes that determine specific crystal characteristics. Results from this research have suggested that the process of crystal formation depends upon a complex process involving more than seven loci, or positions, on a chromosome occupied by genes.

ARS is the U.S. Department of Agriculture’s principal research agency.

Scientific contact: Paul Nakata, ARS Children’s Nutrition Research Center at Baylor College of Medicine, Houston, Texas, phone (713) 798-6782, fax (713) 798-7096,