Dynamics of Galactolipids and Plastids in Nonphotosynthetic Cells of Glycine max Suspension Cultures : A Morphological and Biochemical Study

The age-dependent interrelationship of galactolipids and plastids in heterotrophic cell suspension cultures of Glycine max (soybean) was studied with regard to aging of nonphotosynthetic cells. Cells were propagated in the dark and under illumination with white light, and were harvested at days 7 (end of logarithmic phase), 14, and 21 (extended stationary phase). Electron microscopy revealed in dark-grown cells a proliferating decay of the amyloplast-type plastids, which could be correlated to a decrease of galactolipids. This trend was dramatically reversed in irradiated cultures, where the plastids of day 21 cells appeared rejuvenated. A concomitant increase of galactolipid content in the cells was observed, yet chlorophyll synthesis and photosynthetic activity were not induced. The dynamics of galactolipid contents did not correlate with total lipid contents in dark-grown as well as in irradiated cultures. [³H]Galactose served as a radioactive probe for the subcellular localization of galactolipids by electron microscopic autoradiography. Apart from plastids, galactolipids may also be constituents of the plasma membrane. The results render the heterotrophic cell suspension culture a suitable model to study the impact of senescence on plastids of nonphotosynthetic cells.