A Developmentally Regulated Hydroxyproline-Rich Glycoprotein from the Cell Walls of Soybean Seed Coats

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Abstract
In soybean seeds the level of hydroxyproline is regulated in a developmental and tissue-specific manner. The seed coat contains .apprx. 77% of the total hydroxyproline in the seed at all stages of development. The ratio of hydroxyproline to dry weight was determined in a number of tissues within the seed; only the seed coat shows an increase in this ratio during development. Within the many cell layers of the seed coat, hydroxyproline is most abundant in the external layer. The hydroxyproline is present as a hydroxyproline-rich cell wall glycoprotein. The protein is rich in hydroxyproline (36%), lysine (11%), proline (10%), histidine (9%), tyrosine (9%) and serine (8%). The carbohydrate portion is 90 mol % arabinose and 10 mol % galactose. The arabinose residues are attached to hydroxyproline mostly in the form of trisaccharides. The apparent MW of this glycoprotein is 100,000 daltons.