Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2008
Publication Date: 4/15/2008
Citation: Krishnan, H.B. 2008. Preparative Procedures Markedly Influence the Appearance and Structural Integrity of Protein Storage Vacuoles in Soybean Seeds. Journal of Agricultural and Food Chemistry. 56:2907-2912. Interpretive Summary: Soybeans contain about 35-40% protein on a dry weight basis. These proteins accumulate during mid-stage of seed development and are deposited in protein storage vacuoles (PSVs). Phytic acid, a compound that is generally indigestible by monogastric animals, accumulates in globoid crystals that are found in the PSVs. Soybeans containing low amounts of phytic acid have been generated by mutational breeding and genetic engineering. It is not known if the decrease in the phytic acid in these plants is accompanied by a decrease in the globoid crystals. In this basic study, the presence of globoid crystals within PSVs was investigated with the aid of transmission electron microscopy. The results demonstrate the profound effects of preparative procedures on the ultrastructural integrity of soybean PSVs. The information obtained from this basic study will provide biotechnologists and plant breeders an alternative tool for selecting soybean cultivars that accumulate low phytic acid. Low phytate soybeans used in animal feed could decrease phosphorus levels in manure by 50 percent and significantly reduce environmental phosphorus pollution.
Technical Abstract: In legumes, vacuoles serve as the final depository for storage proteins. The protein storage vacuoles (PSVs) of soybean contain electron-transparent globoid regions in which phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate) is sequestered. Here, I report the effect of preparative procedures on the appearance and ultrastructural integrity of PSVs in soybeans. Electron microscopy examination of both developing and mature soybean seeds that were post-fixed with osmium tetroxide revealed PSVs that had a homogeneous appearance with very few globoid crystals dispersed in them. Numerous electron dense lipid bodies were readily seen in these cells. Omission of osmium tetroxide strikingly altered the appearance of PSVs and aided the visualization of numerous globoids distributed throughout the PSVs. In contrast to the osmicated tissue, lipid bodies appeared as electron transparent spheres. The choice of dehydration reagent or staining procedure had little influence on the appearance of the PSVs. The results of this study demonstrate the profound effect of osmium tetroxide on the appearance and structural integrity of PSVs in soybean.