CHLOROPHYLL CONTENT AND YIELD IN FLASHING LIGHT 



1273 



Emerson and Arnold (1932) found, however, in their first flashing Ught 

 experiments with suspensions of Chlorella pijrenoidosa, that the maximum 

 oxygen production per flash was less than 0.0001 cubic centimeter per flash 

 per cubic centimeter of cells, corresponding to only one molecule of oxygen 

 for each 2660 molecules of chlorophyll! In a second paper (1932) the same 

 observers investigated whether the maximum production per flash had 

 any relation to the chlorophyll concentration at all. For this purpose, 

 they used Chlorella cells grown in light of different intensity or spectral 



c 

 o 



a 



71 

 O 



X 



< 



o 

 o 



UJ 



_) 

 o 



.5 



0.5 1.0 



[Chi], (moles/mm.') x 10^ 



Fig. 32.6. Flash yield and chlorophyll content (after Emerson and Arnold 1932). 



composition (neon tubes, mercury lamps and incandescent lamps). The 

 [Chi] values of these cultures ranged from 4 X 10-^ mole/1, to 16 X lO^' 

 mole/1, (referred to the volume occupied by the cells). The oxygen yield 

 per flash was found to be approximately proportional to the chlorophyll con- 

 tent {cf. fig. 32.6) ; but the proportionality factor (r) was again found to be 

 of the order of 5 X lO-\ and not of the order of unity. In Table 32.1 we 

 list the values of 1/r taken from the fundamental investigations of Emerson 

 and Arnold (1931, 1932), as well as from the subsequent determinations of 

 Arnold and Kohn (1934) and Emerson, Green and Webb (1940). 



The last set of figures in Table 32.1 shows that r was found to decline 

 steadily in aging cultures. (The yield per flash diminished with age al- 

 though the chlorophyll content remained constant or even increased.) 

 This result reminds one of the observations of van Hille on the effect of age 

 on rate of photosynthesis of Chlorella in continuous light (Vol. I, p. 239). 

 Perhaps the striking decline of t also could be checked, at least to a certain 

 extent, by avoiding nutritional deficiencies. With the exception of aged 



