these assays were done were lost some years 

 ago. Their content of ketoglutaric dehydro- 

 genase activity, based on assays of multiple 

 generation cultures in 1953, was not absolutely 

 zero, but about 4% of the level found in the wild 

 type; see Table I). 



J. WRIGHT: They won't respond to any other 

 system you've tried? 



CANTING: That's right. They seemed to 

 have lost the capacity. We would like to think 

 this lesion involved some kind of a "master gene" 

 which exerted pleomorphic effects because so 

 many, many things (including extreme reduction 

 in viability) were associated with this loss of 

 capacity for the formation of an RS cell. 



GRUN: In your discussion, you've been 

 dealing with RS as a unit, as something fairly 

 constant, but in the beginning slides you were 

 stressing RS as being highly variant, oranges 

 ones, light ones, etc. How do you account for 

 the variability in RS? 



CANTING: Well, I didn't stress the varia- 

 bility of RS at the beginning. I stressed that if 

 one starts with a population of spores, they have 

 the capacity to develop along at least four alter- 

 nate pathways, although I may not have said it 

 in so many (or rather so few) words. Spores can 

 develop into RS cells, GC cells, orange cells, or 

 a type which we call "late-colorless" cells. 

 Thus, there are four alternate pathways in the 

 life history of B. emersonii but the ones I have 

 discussed today are the two major ones. 



GRUN: Then was this just one of the changes 

 that occurs in this system? 



CANTING: Let me clarify. (The following 

 was altered slightly in the proof in order to 

 clarify the clarification which involved exten- 

 sive use of the blackboard.) Starting with a pop- 

 ulation of spores on plates, one obtains two 

 main cell types in the first generation; either 

 GC cells or RS cells, depending upon whether 

 or not bicarbonate is present (cf. Fig. 18). 

 Between 99 and 100% of the population of spores 

 will do this. However, depending upon the growth 

 medium selected, up to 0.5% of the population 

 of first-generation plants will consist of what 

 we have called an "G" cell -literally, an orange 

 cell. The cell is orange because, judging from 

 evidence obtained with mutant strains, it con- 

 tains gamma-carotene. Another zero to 0.5% of 

 the population consists of what we have called 

 "late-colorless" cells, cells which differ from 

 GC cells by their much longer generation time. 

 Does this clarify it? I have been speaking of a 

 population of spores, not a single spore. 



GRUN: Then the orange and the late-color- 



TABLE I 



Enzyme system assayed Specific Activity 



(crude cell-free preparations) in 



Fcr derails see reference 5. 



less are not triggered by bicarbonate, but by 

 something else? 



CANTING: It gets fuzzier nowl If we start 

 with an orange cell, harvest all its spores, and 

 plate them out, the new generation of plants has 

 essentially the same composition obtained with 

 the usual population of spores. However, it is not 

 exactly the same; more nearly 1% of the popula- 

 tion now consists of orange cells. From the 

 spores of a late colorless cell, an essentially 

 normal population is also obtained; but, in this 

 case, fewer than average numbers of orange 

 cells are produced. (The reply above was altered 

 slightly in the proofs for purposes of clarifica- 

 tion; the reader is referred to the paper by 

 Cantino and Hyatt cited in the bibliography of 

 this report for detailed tabulations of the kinds 

 of progeny produced by the different cell types 

 of B. emersonii.) 



J. WRIGHT: Are these orange or late color- 

 less cells on the periphery of a culture or are 

 they different in some way? 



CANTING: No, when starting with spores 

 which have been spread out uniformly on the 

 surface of a Petri dish so that each one develops 

 into an individual plant, you find that these vari- 

 ous cell types are distributed essentially at 

 random. We have published some evidence to 

 show that the distribution of a cytoplasmic 

 particle, which we labeled a "gamma" particle, 

 may be involved (3). 



McCARL: I have a question on theglucose- 

 6-phosphate dehydrogenase. Do you feel that it's 

 synthesized on the surface of the membrane? 



161 



