38 



H. TAMIYA et al. 



VOL. 12 (1953) 



+ 0.5 



An interesting fact is revealed when we compare the temperature dependency of 

 ^P, k-Q and ko,. In Fig. 13 are plotted the logarithms of these values against the reciprocals 

 of absolute temperature. At 25°, kj^ is ^ 



about 3 times larger than k-p, which in- +].o 

 dicates that, at that temperature, the 

 (light-saturated) growth rate (^g) is 

 largely determined by the process of 

 photosynthesis. At 7°, on the contrary, 

 k-Q is less than 1/3 of k-p] therefore, the 

 dark reaction represents the main rate- log^^ k 

 determining step in the over-all growth 

 process. At 15° the (light saturated) 

 growth rate is almost equally dependent 

 upon the rates of photosynthesis and the 

 dark reaction. In Fig. 13 are given the 

 magnitudes of the apparent activation 



-0.5 



'1.0 



■1.5 



33 



34 



35 



36 



W 





energy (in kcal.) of each process, calcu- 

 lated from the inclination of the curves 

 in each temperature range. Of great 

 interest is the remarkable temperature 

 dependency of the dark process, and 

 especially that at lower temperature, 

 which corresponds to an apparent 

 activation energy of as much as 49 kcal. 

 The physico-chemical implication as well as the physiological significance of this re- 

 markable phenomenon is indeed a problem which is worth while to be studied in the 

 future. 



Fig. 13. Temperature dependency of the rate of the 

 dark process and the Hght-saturated rates of growth 

 and photosynthesis. The figures given on the curves 

 indicate the apparent activation energies in kcal. 

 calculated from the inclination of curves at tlie res- 

 pective temperature spans. 



SUMMARY 



1 . Observations on the culture of Chlorella have revealed that the algal cells assume two distinct 

 forms in the course of their growth. One form, which we called "dark cells", is smaller in size, richer 

 in chlorophyll content, and stronger in photosynthetic activity than the other, which we referred to 

 as "light cells". When illuminated, dark cells grow and, with a substantial increase in mass, turn into 

 light cells; the latter, when ripened, bear autospores in themselves (on the average 6-7 per cell) and 

 eventually burst setting free the autospores which then become individual dark cells. The transforma- 

 tion of light cells into dark cells involves no increase of cell mass and occurs only under aerobic condi- 

 tions, irrespective of whether the cells are in the light or in the dark. The dark cells freshly born from 

 light cells are somewhat smaller in size and contain less chlorophyll than the "active" dark cells, into 

 which the former turn rapidly imder the influence of light. 



2. The processes of transformation between these types of cells were investigated separately under 

 various experimental conditions, and it was concluded that (i) the main event occurring in the trans- 

 formation of dark cells into light cells is pliotosynthcsis, although it is accompanied by some other 

 metabolic processes, which are to be distinguished from the photosynthetic process in the ordinary 

 sense ; and that (ii) the transformation of light cells into dark cells involves a light-independent and 

 aerobically cndergonic anabolic metabolism, although, when illuminated, the transformation is 

 accompanied also by some photosynthetic processes. 



3. The steady state of growth, as it is affected by light intensity and temperature, was investigated 

 in detail, and its rate was compared with the photosynthetic rate using a common unit of measure- 

 ment, i.e., in terms of weight of organic matter synthesized per unit time and per unit weight of cells. 



References p. 40. 



