160 



R. P. Levine 



ultra-violet light, followed by screening for their inability to fix carbon dioxide 

 in the light^'^\ Unlike the wild type strain, each of the mutant strains will not 

 grow in minimal medium unless it is supplemented with sodium acetate^^^). 



Four different mutant strains will be considered here; namely, ac-21, 

 ac-115, ac-141, and ac-208 (the symbol ac refers to acetate dependence). With 

 the exception of ac- 14r and ac- 208 , the mutants lie in different linkage groups. 

 Although ac-14l"and ac- 208 "are linked they lie about 10 map units apart on 

 opposite sides of the "centromere in linkage group III (see references 19 and 20 

 for details of the techniques of genetic analysis). In terms of current genetic 

 theory, each mutation should be located in a different cistron or functional unit. 

 That is, each mutation most likely represents a genetic alteration that affects 

 the synthesis or activity of a different enzyme. 



These mutant strains, while unable to fix carbon dioxide by photosynthesis 

 at the wild type rate, resemble wild type in two important characteristics. 

 First, electron microscopy has revealed that ac-21, ac- 115 and ac- 141 have 

 normal chloroplast structure^^l); ac- 208 has not been examined. Second, there 

 are no major differences in chlorophyll content^^^'. There are, however, minor 

 differences in carotenoid content, but these may be trivial in so far as their 

 being causally related to the inability of the mutant strains to carry out normal 

 photosynthesis^ 13). 



REACTIONS OF THE 

 ELECTRON TRANSPORT SYSTEM OF PHOTOSYNTHESIS 



The rationale of the experiments with the mutant strains of C. reinhardi 

 is simply one of inquiring into which known reactions of photosynthesis whole 

 cells or isolated chloroplast fragments can or cannot perform, and then attempt- 

 ing to reconstruct the sequence of reactions which best fits the observed results. 

 Thus, we are following, by analogy, one of the classical procedures of bio- 

 chemical genetics to determine the sequence of events as they occur in a partic- 

 ular biosynthetic pathway. 



Except for recently obtained data pertaining to the mutant strain ac-208, 

 and to both photoreduction and photophosphorylation as they relate to wild type 

 and the four mutant strains, the results summarized here are discussed in a 

 series of publications'"' °" ^ 1' '■^K 



Carbon dioxide fixation in whole cells 

 by photosynthesis and photoreduction 



It has been shown that, in comparison to the wild type strain, whole cells 

 of the mutant strains are highly deficient in their ability to fix carbon dioxide 

 by photosynthesis^^). The maximum rate of fixation by a mutant strain (ac-21) 

 was about two per cent of the wild type rate. 



