Diversity at the Subcellular Level and Its Significance 155 



cytoplasm is altered. The discrete clumps of densely staining material 

 become less discrete and the components seem to become more 

 diffusely distributed in all cells of the lobule as they are normally 

 in cells bordering the portal areas. One might conclude from this that 

 rather pronounced changes would be found in the form and distribu- 

 tion of the rough form of the endoplasmic reticulum. Actually, when 

 examined I Porter and Bruni, unpublished) in the electron micro- 

 scope, the phenomenon is found to be referable to the distribution of 

 mitochondria relative to the cisternae of the ER. In the relatively 

 quiescent cell of the normal animal, the cisternae tend to appear in 

 clusters of 8 to 12 units in parallel array (Figs. 13A and 13B). These 

 would reasonably correspond to the discrete basophilic bodies of the 

 light microscope image. In the plasmaphoresed animal, on the other 

 hand, one finds these clusters of cisternae invaded by mitochondria 

 and thus more widely separated (Fig. 13B ) which, from an examina- 

 tion of adjacent thick and thin sections, can be seen to account for 

 the diffuse basophilia of the stained cells. Thus in response to de- 

 mands for increased synthesis of plasma proteins, the structural ele- 

 ments of the ergastoplasm take on a more intimate association with 

 the mitochondria, presumably for the ATP required. Here again it 

 is to be noted that within the limits of this modulation, the pattern of 

 organization exhibited by the ER departs from the normal only to 

 admit the mitochondria to the intercisternal spaces in the otherwise 

 characteristic clumps or clusters of cisternae. 



The ER in differentiation 



The diverse forms which have been described and illustrated here, 

 and in most published descriptions of this system, are found in fully 



FIG. 12A. Portions of two cells from a normal cockerel liver. The picture shows 

 the typical form of the endoplasmic reticulum in the liver cells of this animal. 

 Single cisternae with associated ribosomes are wrapped around the mitochondria. 

 A few vesicles of the agranular type are mixed with the glycogen (gl). Micrograph 

 from class project, graduate-student course in cell biology. Magnification: 20.000 X. 

 FIG. 12B. Liver of cockerel 4 days following injection of estrogen. Among other 

 changes induced by this treatment, there is a pronounced increase in the amount 

 of the rough form of the endoplasmic reticulum. The cells come to resemble more 

 closely those of the hen's liver, and the plasma requires lipoproteins and phospho- 

 proteins found normally in the laying hen. These are synthesized for egg-yolk 

 production. Thus exogenous estrogen induces marked proliferation of the rough ER, 

 but the pattern of distribution and mitochondrial association remains similar to 

 that in hen and cockerel. The nucleus is indicated at N, the mitochondria at M, 

 spaces of Disse at Di, rough ER at rer. (Complete observations in press.) Magnifi- 

 cation: 23.000 X. 



