Cereal Chem 59:336 - 343.  |  VIEW ARTICLE
Protein Secretion in Wheat Endosperm---Formation of the Matrix Protein.

D. B. Bechtel, R. L. Gaines, and Y. Pomeranz. Copyright 1982 by the American Association of Cereal Chemists, Inc. 

The deposition of protein into vacuoles in the starchy endosperm of hard red winter wheat was studied using transmission electron microscopy and enzymatic digestion of thin sections. Protein bodies that formed in the cytoplasm were transported to the central vacuole where the protein body membrane and tonoplast fused and deposited the granule of protein into the vacuole. The protein granules in the vacuole enlarged by three mechanisms: addition of membranous vesicular material of various types; addition of flocculent material; and fusion of the granules with other newly deposited protein granules. The fusion process occurred rapidly after 17 days after flowering and resulted in the conversion of the spherical protein granules into irregularly shaped protein masses that eventually became the matrix protein. Enzymatic digestion of thin sections revealed that the contents of dense-cored Golgi vesicles and protein bodies were susceptible to protease VI and pepsin but not to alpha-amylase. The vacuolar protein granules were almost completely digested with protease VI and pepsin. The only undigested regions were peripheral densely stained inclusions thought to be the last added protein.