172S 



CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



Aspidistra, consist of only two layers of macromolecules, as represented 

 schematically in fig. 37A.15. (The same structure can be suggested also 

 for the bands or shells of approximately the same thickness, observed in 

 Mougeotia and Chlorella, respectively'. ) 



This conclusion was drawn from the observation of the transformation 

 of the grana, suspended in 1 M sucrose solution, caused by dilution with 

 water. Under the phase contrast microscope the grana could be seen swell- 

 ing, flaking off, and growing into long strands; the fluorescence microscope 



Fig. o7.\..ItJ. Cluuiitf ol culluiJsL'tl \y.ig^, ubUauL'tl Ironi a graiium of Aspidrntia by 

 treatment in distilled water (after Frey-Wyssling and Steinmann 1953). Fixed in 1% 

 Os04, chromium shadowed. It is suggested that this is a "monej^ roll" (Fig. 37A.8) in 

 which each protein "coin" has swelled up by penetration of water between two mono- 

 laj-ers (Fig. 37A.15), precipitation membrane has formed on the outside, and the bags 

 have collapsed. 



showed that the latter still carried the chlorophyll. Under the electron 

 microscope the strands appeared to consist of round, collapsed, and folded 

 bags, about 1 n in diameter (fig. 37 A. 16). These bags were interpreted 

 as the protein "discs," similar to those shown in fig. 37A.8, which had 

 swollen into bubbles in water and then collapsed. The growth and col- 

 lapse of the grana bags was considered by Frey-Wj^ssling and Steinmann as 

 an indication that the grana had originally consisted of two layers of 

 macromolecules (as shown in fig. 37A.15) which have been pushed apart by 

 the osmotic pressure of water penetrating into the space between them. 

 The fine granulation, observed on the best electron micrographs of the grana 

 surface, suggests that these macromolecules are spherical; they could not 

 3'et be measured exactly, but certainly are under 0.0 1 fx in diameter, and 

 must therefore have a molecular weight of <400,000. 



The "laminated" chloroplast structure again appeared in Wolken and 

 Palade's (1952, 1953) investigation of two flagellates — protozoans which 



