563 



Lawrence Bogorad, Frank V. Mercer, and Rosemary Mullens 



a slightly more open organization. Chloroplasts in mature cells 

 of III-C (Figure 3), a strain which lacks phycobiliproteins, are 

 only slightly less organized than those of III-D-2 and the wild- 

 type. 



Considerable variation in the orderliness of the lamellar 

 system is observed in these three cell types. This may be re- 

 lated to the angle of sectioning or the age of the cells; a 

 breakdown of structure has been observed in cells of old cul- 

 tures. (Prior to division a complete disorganization of the la- 

 mellar system and chloroplast also occurs, but these changes 

 are not relevant to the present discussion.) Thus, from a com- 

 parison of III-D-2, III-C, and wild-type cells, it seems that 

 phycobiliproteins are not essential structural elements of the 

 photosynthetic lamellae, nor are they necessary for the over- 

 all organization of the lamellar system of the mature chloro- 

 plast. 



In mature cells of mutant GGB, a strain which lacks chloro- 

 phyll a but contains phycobiliproteins, the lamellae have a unit 

 membrane structure similar to that in III-D-2 and wild-type (Fi- 

 gure 4c) but they are usually shorter a few hundred A to a- 



bout a micron in length. In general the lamellar system is less 

 well organized than in the other strains described (Figure 4): 

 In the peripheral region of the chloroplast, the lamellae are 

 frequently arranged in parallel rows of about the same length as 

 in wild-type and occasionally (Figure 4b) most of the lamellae 

 show parallel arrangement. Usually in the main body of the 

 chloroplast, however, the lamellae are much shorter. The smal- 

 ler pieces tend to be scattered at random, while the larger 

 pieces tend to be parallel but with a wavy orientation. The 

 total amount of lamellae, as represented by the profiles of the 

 segments in the sections, is much less than in wild-type or III- 

 D-2, possibly less than a quarter. In some sections large areas 

 of the chloroplasts contain only a few short lamellae. The ma- 

 ture chloroplasts are similar in size to those in wild-type, but 

 have a more irregular shape. The limiting membrane is not al- 

 ways distinct and tends to merge with the cytoplasmic membranes. 

 Because of this, the chloroplasts in GGB are not as clearly 

 differentiated from the cytoplasm as in III-D-2, wild-type, and 

 III-C. 



The mutant GGB-Y has a structure similar to GGB, but its 

 chloroplast is much less organized (Figure 5). The chloroplasts 

 are irregular in shape; the limiting membrane is frequently dis- 

 continuous so that the lamellae often merge into the cytoplasm. 



