ULTRASTRUCTURAL CHANGES OF MEMBRANES WITH HYDRATION IN SOYBEAN SEEDS

Structural changes of soybean seeds at various levels of hydration were examined for possible explanations of the rapid initial leakage of solutes during imbibition. A clustering of vesicles and lipid bodies was observed along the two types of membranes which must undergo most extensive enlargement: the plasmalemma and the protein bodies. There was no such association with the membranes of nuclei, plastids, and mitochondria. Freeze fracture replicas of tissue with less than about 18% water content yielded only small areas identifiable as plasma membrane and these contained many irregularities or pock marks. As imbibition proceeded, larger expanses of plasma membrane were revealed. The increase in water content was seen to remove the irregularities of the membrane plane, and generally was associated with an extensive increase in particles embedded in the membrane sheets. It is suggested that imbibition may involve rapid and extensive incorporation of new materials into expanding membranes of the cell, including addition of lipids and possibly of proteins.