Development of protein bodies in oat starchy endosperm

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Abstract
The development of protein bodies in the starchy endosperm of oat (Avena sativa L.) was studied by an ultrastructural examination of the subaleurone layer at various stages of maturation. In caryopses of 11 mg fresh weight, cells were highly vacuolate with little evidence of protein deposition. By 18 mg, vacuoles were smaller, rough endoplasmic reticulum (RER) was evident, and some vacuoles contained protein deposits. As the caryopsis matured, protein deposits filled a greater proportion of the vacuolar space. Small protein deposits were observed within the cistemae of the RER, and direct connections between the RER and the tonoplast of vacuoles were evident. Dictyosomes were infrequently observed at any stage. The electron micrographs are consistent with the hypothesis that protein synthesized on the membrane-bound ribosomes is transported within the ER cisternae to the vacuoles, where it condenses, forming protein bodies.