Production of Multiple Vacuoles as an Early Event in the Ontogeny of Protein Bodies in Developing Soybean Seeds1

Abstract

We have made an ultrastructural study of developing soybean seeds, cultivar Wells [Glycine max. (L.) Merr.], using light and electron microscopy in an attempt to resolve the question of protein body ontogeny. Formation of numerous small vacuoles from the central vacuole was observed as early as 17 days after flowering (DAF). The process continued until each cell contained many small vacuoles. There was a close association between development of rough endoplasmic reticulum (RER) and Golgi bodies and the appearance of protein bodies. Proliferation of RER was observed by 34 DAF, and the vacuoles filled with reserve protein to form distinct protein bodies. Many small vesicles were derived from RER and Golgi bodies but these did not appear to develop into protein bodies. These vesicles may be concerned with transport of storage protein to multiple vacuolar sites for deposition of reserve protein into protein bodies. Protein bodies increased both in size and number as the seed developed. At later stages of seed development, around 60 DAF, RER disappeared and many large protein bodies and numerous lipid bodies were visible in cotyledon cells. The results of our study demonstrates the following: (i) early subdivision of the central vacuoles (17 DAF) appears to be the source of protein bodies; (ii) there is no apparent physical connection between the RER and protein bodies; (iii) accumulation of starch and lipid reserves in soybean seed clearly precedes that of storage protein; (iv) appearance of membrane‐bound polyribosomes (not free ribosomes) is consistent with the onset of storage protein; and (v) at physiological maturity, most cell organelles had disappeared.