|Hurkman Ii, William|
Submitted to: Plant And Cell Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2004
Publication Date: 4/1/2004
Citation: Wong, J.H., Cai, N., Tanaka, C.K., Vensel, W.H., Hurkman, W.J., Buchanan, B.B. 2004. Tioredoxin reduction alters the solubility of proteins of wheat starchy endosperm: an early event in cereal germination.. Plant And Cell Physiology.2004. 45: 407-415 Interpretive Summary: Thioredoxins are proteins that are universally present in all organisms. They function in a number of regulatory processes, including photosynthesis, seed germination, transcription, and cell division. In cereal seeds, it is known that thioredoxin reduces disulfide bonds of target proteins, which, in turn, increases the susceptibility of storage proteins to proteolysis and alters enzyme activities. In addition to these regulatory roles, this study provides evidence that thioredoxin increases the solubility of a number of wheat endosperm proteins, including the storage proteins. This increase in solubility promotes storage protein mobilization, an important prerequisite for germination and seedling development.
Technical Abstract: A KCl-soluble, albumin/globulin fraction of wheat (Triticum aestivum L.) starchy endosperm was further separated into a methanol-insoluble fraction that contained metabolic proteins and a methanol-soluble fraction that contained 'chloroform-methanol' or CM-like proteins. Reduction of the disulfide bonds of the CM proteins with thioredoxin or dithiothreitol altered their properties so that, like the metabolic proteins, they were insoluble in methanol. Glutathione had little effect, indicating dithiol specificity. Proteomic analysis of the CM protein fraction revealed the presence of isoforms of low molecular weight disulfide proteins (a-amylase, a-amylase/trypsin and WCI proteinase inhibitors, lipid transfer proteins, g-thionins), stress enzymes (Cu-Zn superoxide dismutase and peroxidase) and storage proteins (g and w-gliadins, low-molecular-weight glutenin subunits and globulins of the avenin N9 type). These findings support the view that, in addition to altering activity and increasing protease sensitivity, reduction by thioredoxin increases the solubility of proteins, thereby promoting processes of the grain starchy endosperm, notably the mobilization of reserves during germination and seedling development.