Studies on the Growth in Culture of Plant Cells

Abstract

A technique has been developed for the electron microscope study of the free cells and small cell aggregates of suspension cultures of Acer pseudoplatanus, L. Changes in fine structure have been followed during the growth of a batch culture over 24 days, covering the lag phase, the phase of exponential growth, and the stationary phase to a condition where the cells show evidence of senescence. During the lag phase there is a massive synthesis of new cytoplasm and an increase in the number of mitochondria and ribosomes. By the point of transition to the phase of exponential growth many of the ribosomes are either attached to the ER membranes or are organized in spherical or spiral clusters. Multivesicular bodies are frequently observed. The development of the cell plate can be followed in some detail at this stage. As the rate of cell division decreases and cell enlargement begins the cytoplasm comes to constitute a thin lining layer with fewer ribosomes, less prominent ER membranes and apparently fewer mitochondria. At this time starch begins to form and the frequency of lipid (or protein) bodies and of membrane enclosed crystals increases. During the stationary phase, which begins at about the 15th day of culture, the old cell walls show characteristic changes and are frequently ruptured. Intra-cytoplasmic vacuoles appear and then with the continuation of culture disappear as the cytoplasmic layer approaches its minimum thickness. Nuclei show invaginations and these often contain characteristic ‘aged’ mitochondria.