The Fine Structure and Function of Associations of the Endoplasmic Reticulum, Chloroplasts and Plasmalemma in Cultured Protoplasts of Skimmia japonica Thunb

Abstract

Mesophyll protoplasts of Skimmia japonica leaves were isolated and cultured in a liquid medium. Changes occurring in the chloroplasts during isolation and culture of the protoplasts were followed by electron microscopy using the thin section and freeze-etching technique.
During isolation protein crystals appeared in the chloroplasts. In cultured protoplasts a decrease in the number of thylakoids and an increase in the volume of the chloroplast stroma was detected. Upon longer incubation the number of the chloroplasts became reduced. In numerous chloroplasts lipid droplets accumulated and concentric thylakoid structures were formed.
The most striking result was the appearance of some peculiar aggregates of membranes at the periphery of the chloroplasts. It is supposed that these structures constitute profiles of aggregated tubules of smooth endoplasmic reticulum. Frequently there exists a close proximity between these tubules and rough endoplasmic reticulum profiles which are in contact with the plasmalemma. The rough endoplasmic reticulum seems to be a chain between the tubules and the plasmalemma. Possible functional relationships between the described organelles and explanation of membrane proliferation at the periphery of the chloroplasts are discussed.