Biochemical and Cytological Observations on Chloroplast Development

Abstract

Prolamellar bodies (PLBs) of etioplasts of Avena sativa are made up of tubules, which compose a highly organized crystal-like system. After isolation of pure PLBs we solubilized the PLB-membranes completely with Na-dodecylsulfate (SDS). Using the -negative stain- technique we again observed in the electron microscope the presence of tubules a short time after the dissolution of the lipoprotein complexes. The first examinations of this phenomenon led to the following results: 1. The PLBs are completely dissolved by heating in a solution with a high ratio of detergent to protein. 2. The dissolved components can reaggregate into tubules during undisturbed incubation of the solution even in the presence of detergent. The speed of reaggregation is de- pendent upon the protein/SDS - ratio and the temperature of the incubation. The aggregates display the same structures and inner diameters as the native tubules. 3. Depending on incubation time and temperature of the solution, changes in the most predominantly visible structures are as follows: a) Temperatures between 12 °C and 20 °C: In the first days the growth of mostly straight and of only a few branched tubules was visible. Often these tubules bind laterally. b) Temperatures between 25 °C and 40 °C: The straight unbranched tubules are less often visible. Soon (3 rd-5 th day), branched aggregates appear which can form large tubular complexes. In the course of a longer incubation time (about 30 days) aggregates of fusing netlike structures and long tubules are formed. Experiments of other authors have shown, that PLBs were reconstructed into elongated tubules when exposed to light during cold treat- ment, which only very slowly fuse into thylakoids. In addition, our system shows the presence of mainly elongated tubules at low temperatures. The strong tendency of the