564 



' 



Lawrence Bogorad, Frank V. Mercer, and Rosemary Mullens 



Thus, the chloroplast in GGB-Y does not appear as a distinct 

 organelle sharply differentiated from the cytoplasm. Rather it 

 resembles a collection of loosely arranged lamellae more or less 

 aggregated into a discrete body; yet in some cells the area oc- 

 cupied by this aggregation is about equal to that of a well 

 organized chloroplast. The individual lamellae have the usual 

 double membrane structure (Figure 5c) but are shorter than in the 

 other mutants, varying from less than a few hundred K to about a 

 micron in length. Some of the larger lamellae have a parallel 

 orientation (Figure 5b) . Usually the orientation is irregular 

 with the lamellae in the peripheral regions often extending into 

 the cytoplasm. 



Conclusions 



1. The pigments chlorophyll a, phycocyanin, and allophy- 



cocyanin do not appear to be essential structural components 



of the unit membrane. 



2. Since the structural integrity of the lamellae does not 

 involve the pigments, it is possible that the pigments normally 

 found in the lamellae may be added to preformed membranes during 

 chloroplast development. 



3. The amount of lamellar material and its degree of organi- 

 zation varies among the mutants studied in the following order: 

 III-D-2> Wild-type and III-C > GGB > GGB-Y. Thus, although pig- 

 ments are not essential components of the lamellae, their pre- 

 sence affects the extent and organization of the lamellar system . 

 It is possible, however, that the low degree of chloroplast or- 

 ganization in GGB and GGB-Y cells may be related to their hetero- 

 trophic state. The presence of fewer lamellae and their poor 

 orientation may result from the absence of photosynthetic acti- 

 vity. 



4. It has not been possible, from an examination of this set 

 of mutants, i.e. by comparing cells of the wild-type with III-C 

 or GGB with GGB-Y, to determine the normal location of the phyco- 

 biliproteins in the chloroplast of C. caldarium. 



5. Since the unit membrane is the basic structural unit of 

 the cytoplasmic photosynthetic lamellae of the blue-green algae, 

 the photosynthetic lamellae of chloroplasts, and the photosyn- 

 thetic lamellae of Cyanidium , it can be assumed that some of the 

 conclusions reached for this alga are generally applicable. That 

 is, chlorophyll a is neither an essential structural component of 



