34 



H. TAMIYA et al. 



VOL. 12 (1953) 



TABLE II 



MAIN QUANTITATIVE DATA REGARDING THE EFFECT OF LIGHT AND TEMPERATURE UPON THE RATES OF 

 PHOTOSYNTHESIS AND GROWTH AS WELL AS THE DARK CELL RATIO IN THE CULTURE 



Temperature 

 (C) 



Light-limited 



rate: a 

 (ijday-kilolux) 



Light-saturated rale 

 (z/day) 



Half-saturating light intensity 

 (lux) 



Photo- 

 synthesis 



Growth Photosynthesis 



Grouih 



Photosynthesis 



Grouth 



Dark cell ratio 



(/I ) at saturating 



light intensity 



25^ 



7' 



0-45 



1.79 

 0.86 

 0.40 



1. 19 

 0.49 

 0.09 



2400 



1200 



500 



1600 

 600 

 no 



0.66 



0.55 

 0.38 



THEORETICAL CONSIDERATIONS 



All the evidence described above supports the conclusion that the growth process 

 — increase in cell number and in total mass — of Chlorella is accomplished by a repetition 

 of the "life cycle" involving the change between dark cells (nascent and active) and light 

 cells (non-sporulated and sporulated) as it is schematically represented by the diagram 

 in Fig. II. Symbolically, and neglecting the fact that there are two kinds each of 

 dark and light cells, the process may most simply be expressed by the following 

 formulae : ^ 



D — ^^L 



LIGHT 



CELL 3 



Fig. II. Schematic representation of 

 the mutual transformation between 

 liglit and dark cells in the life cycle 

 of growing Chlorella cells. White 

 arrows indicate the light processes, 

 while black arrows show the processes 

 that can occur both in the light and 

 in the dark. Sizes of circles correspond 

 approximately to the relative sizes of 

 cells and the extent of darkening 

 indicates the relative photosynthetic 

 activity. 



^D 



nT> 



(I) 



(2) 



where D and L represent the dark and light cells 

 respectively, k-^ the rate constant of the increase of 

 cell mass in the formation of light cells from dark 

 cells, and k-^ the rate constant of the increase in cell 

 number in the transformation of a light cell into a 

 number [n) of dark cells. Since the key part of the 

 first process is photosynthesis and the photosyn- 

 thetic activity of dark cells is several times stronger 

 than that of light cells, it is not unreasonable to 

 substitute for k-^ in the above formula the photo- 

 synthetic rate k^ which we have determined with 

 dark cells*. Then, the rates of change in the number 

 of light and dark cells in processes (i) and (2) are 

 expressed by 



d[L] 



d^ 

 d[D] 



n - 1 



I 



n~ 1 



(^p[D] - 



A'd[L]) 



^p[D]) 



(3) 

 (4) 



d^ 



where [L] and [DJ are 



dark cells, respectively, in unit volume of culture**. 



The total number (.V) of cells in unit volume of 



the numbers of light and 



* and ** See the footnotes on page 35. 

 References p. 40. 



