1960 



KINETICS OF PHOTOSYNTHESIS 



CHAP. 37D 



(For more detailed discussion of the induction results, see chapter 33, sec- 

 tion A2.) 



Experiments of this type were made with varying intensities of illu- 

 mination. If an average respiration correction was applied to the rates ob- 

 tained at different light intensities (or a single "best fitting straight line" 

 was used for the whole dark or light period), the light curves, P = J{I), 

 calculated in this way, showed a "Kok effect" — i. e., their slope changed 



z 

 o 



o 



> 



UJ 



z 



UJ 



o 



>- 



X 



o 



u. 



o 



UJ 



cr 



100 

 90 

 00 



70 



60 



50 



40 



30 



20 



10 







-10 



-20 



-30 



-40 



-50 



; 



I I r— I r- 



UI6HT 



,.V 





-1 rill 



DARK 



-I — I I I I 

 LIGHT 



^a^rfJV^ 



•*^> 



I I — I — I — r 

 DARK 



r 



LIGHT 





A", 



#/v/ 



<>)/<*.% **' ■•. 



— I I I 

 DARK 



8 10 12 14 16 18 20 22 24 26 28 30 32 34 

 TIME-MINUTES 

 Fig. 37D.32. Rate of photosynthesis calculated from the same data as in fig. 37D.31, 

 by interpolating respiration during the light periods as shown by dashed lines (i. e., 

 by connecting by logarithmic curves the respiration level at the end of one dark period 

 with that at the beginning of the next dark period, but disregarding the "oxygen gulp" 

 in the first 1-2 minutes of darkness) (after Brackett et al. 1953'). The so calculated rate 

 of photosynthesis is constant except for an induction period of about 2 min. in the first 

 light period, dropping to < 1 min. in the two following light periods. 



abruptly, by about a factor of two, near the compensation point (c/. p. 

 1113). If, however, the respiration course during the light period was 

 evaluated point-by-point as described above, attributing all variations in 

 the net gas exchange (outside the "induction periods") to changes in res- 

 piration, the "Kok effect" disappeared, and the Hght curves became 

 straight lines. (This procedure amounts to calculating the rate of photo- 

 synthesis by adding to the rate of oxygen liberation at the end of a Hght 



