1468 



PHOTOSYNTHESIS IN INTERMITTENT LIGHT 



CHAP. 34 



It could be hoped that a satisfactory explanation of these additional 

 features of induction will also provide an interpretation of the additional 

 intermittency effects, supplementing rather than replacing the original 

 one. One could also hope that cell cultures showing no CO2 supply limi- 

 tations, and Uttle or no "transients" would also show little or no compUcation 

 of the Emerson-Arnold-Frank mechanism of flash saturation. 



o 



E 



Q. 4 





25° P""" -. 7.3 xlO" 



15° P"""" = 5 3 X 10" 



70 pmax.^ 3-7^ iQ- 



200 



400 600 



f, lux sec. 



800 



1000 



1200 



Fig. 34.22. Yield of flashes (with saturating dark intervals) in Chlorella ellipsoidea 

 as function of flash energy (after Tamiya and Chiba 1949); for units, see preceding 

 figure. (Closer approach to the extrapolated saturation level than shown in this figure 

 is indicated by data in text of paper.) 



We now have to discuss several flashing hght studies which seem to call 

 for a more thorough revision of the concepts derived from the above-enum- 

 erated earlier observations. The most important of them is an investiga- 

 tion by Tamiya and Chiba (1949). They used Chlorella ellipsoidea, a 

 species similar to Chlorella pyrenoidosa of Warburg and Emerson. The 

 cells were grown for 10 days in Knop's solution at 2-3 klux, and then incu- 

 bated in the dark for 3 days. Its maximum steady photosynthesis at 

 25° C. in carbonate buffers was about 1.5 Aimole/sec. per gram dry weight 

 (0.77 fjivaole at 15° and 0.38 jumole at 7° C). If one assumes a chlorophyll 

 content of 5% (cf. table 25.1), this corresponds to an assimilation time of 33 

 sec. (at 25° C.) typical of normal shade cells {cf. table 28. V). 



Tamiya and Chiba exposed these cells, in buffer No. 9, to flashes of 0.6 

 to 8 msec, duration, obtained by means of rotating discs, on which the image 

 of a 750 watt incandescent lamp was focussed. The maximum illumina- 



