Skip to main content
ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #81458
Title: CALCIUM OXALATE CRYSTALS IN DEVELOPING SOYBEAN OVULES

Author
item HARSLAN, H - IOWA STATE UNIVERSITY
item PALMER, REID
item HORNER, H - IOWA STATE UNIVERSITY

Submitted to: Scanning Microscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soybean seeds, like all other seeds, form in flowers from a small organ called an ovule. The ovule consists of nutritive tissue that surrounds an embryo which will eventually become a new plant. As the ovules develop into seeds, nutritive substances from other parts of the older plant pass into the ovules, and they are used for growth of the embryo and production of storage reserves for when the embryo begins to develop into a new plant In soybean, calcium is transported into the ovules where it probably causes an unusually large amount of a substance called oxalate to form. The increase of oxalate and calcium were monitored by two methods. Most of the oxalate binds wit the calcium to form crystals similar to those found in kidney and bladder stones in humans and animals. These crystals are not detrimental to the developing ovules or embryos, but form and disappear in an orderly fashion. Our research suggests that the oxalate serves to bind with and store excess amounts of calcium for later use by the growing embryos. In addition, we believe that the unbound oxalate, and that which is released from the crystals when they disappear, is somehow used for storage protein synthesis. It has been assumed for many years that oxalate is only a waste product of little or no value to biological systems. Our research indicates that oxalate may, in fact, be very important to the well being of developing soybean seeds, as well as to other plant organs and tissues. Scientists engaged in studying seed development and mineral composition now have evidence that calcium is not just a metabolic by- product. The increase and subsequent disappearance of calcium in a programmed manner has important biological functions which remain to be determined.

Technical Abstract: Ovules of soybean contain massive amounts of calcium oxalate monohydrate crystals during their development. A test for calcium and calcium oxalate indicated a buildup of calcium deposits and crystals in the funiculus where the vascular strand enters the ovule. Crystals increase in the integuments until the embryo enlarges and crushes the innermost portion of the integuments, at which time crystals appear in the developing cotyledon tissues and embryo axis. The crystals form in the cell vacuoles. Dense bodies and membrane complexes were evident in the funiculus. In the inner integument, vacuoles assumed the shape of the future crystals. This presumed predetermined crystal mould is reported here for the first time. As crystals near maturity, walls form around each crystal encasing it. This crystal wall becomes contiguous with the wall surrounding the cell. Integument crystals remain intact until the enlarging embryo begins to crush them. It was shown quantitatively in a related study that the percentage of oxalate by dry mass in the developing ovules reached 24%, and then decreased prior to ovule maturity. Crystal formation and disappearance are an integral part of developing soybean ovules and our data suggest a calcium storage function for the rapidly enlarging embryo.