VOL. 12 (1953) 



GROWTH OF Chlorella 



31 



lux). Within the first several hours of illumination, 

 there occurred a slight increase of cell volume and a 

 sudden increase in chlorophyll content of cells, while 

 the cell number remained unchanged. The resulting 

 cells had the typical characteristics of active dark 

 cells which are encountered in ordinary (continuously 

 illuminated) cultures. This state, however, did not 

 last long on continued illumination, because the ac- 

 tive dark cells further turned into light cells, which 

 is evidenced by the decrease in dark-cell ratio as 

 well as in chlorophyll content of cells. It is worth 

 noticing that both the total amount of chlorophyll 

 and assimilated phosphorus in the culture suddenly 

 increased on illumination. This may suggest two 

 possibilities; either the anabolic metabolism has 

 been accelerated considerably by abundant supply 

 of photosynthate, or the anabolic metabolism might 

 have involved some photochemical process other 

 than photosynthesis in the ordinary sense. 



Fig. 7. Increase in chlorophyll content (and apparent 

 constancy of phosphorus content) of cells during 

 the transformation of light cells into dark cells in 

 the dark. The starting material was prepared from 

 a dark-cell-rich culture (J = 0.99) which was illu- 

 minated with 22,000 lux at 14° C for 55 hours. 

 The resulting light-cell-rich culture {A =0.11) was 

 resuspended in normal medium, and the main exper- 

 iment was conducted at 25° C, with provision of 

 COj-enriched air, first in the dark for 53 hours, 

 and then in the light (20,000 lux) for 12 hours. 



h 2.0 



u. 15 

 o 



30 



^ 20 



S 



A 



PHOSPHORUS I ^s 



CONTENT OF CELLS 



TOTAL CHLOROPHYL 

 IN CULTURE. 



TOTAL ASSIMILATED ' 

 PHOSPHORUS I 



J L 





10 20 30 40 



HOURS IN THE DARK 



50 5 10 15 

 HOURS IN 

 THE LIGHT 



The rate of growth in steady state as compared with photosynthetic rate at different tempera- 

 tures and under different light intensities 



Effects of temperature and the light intensity upon the steady-state rate of growth 

 were investigated with the special precautions described already. In parallel, the photo- 

 synthetic rate as it is affected by the same environmental factors were determined 

 using exclusively active dark cells as material.* 



The conditions applied in both series of experiments were the same except for the point that the 

 medium used in the photosynthetic measurements was deprived of nitrogen in order to prevent the 

 occurrence of growth during the measurement. The temperatures investigated were 7°, 15° and 25° C. 



The results of a large number of measurements are summarized in Fig. 8, in which 

 the growth rate {k^ and photosynthetic rate (^p) are plotted, on a common scale, 

 against the light intensity. Each value presented is the average of several measurements. 

 These results lead us to the following conclusions : 



I. As far as the shape of the curves is concerned, the rate-light intensity relation- 

 ships at different temperatures are fundamentally the same for photosynthesis and 



In all photosynthetic measurements, cell samples showing the dark cell ratio of 0.95 to i.oo 

 were used. 



References p. 40. 



2 



