1396 



INDUCTION PHENOMENA 



CHAP. 33 



influence of variations of cyanide concentration. With sufficient cyanide 

 present, the decay disappears entirely and the fluorescence becomes sta- 

 bihzed at the level it had reached in the second maximum. (The influence 

 on the first fluorescence wave is scarcely noticeable in this figure.) 



Wassink and Katz used the cyanide-poisoned cells for the study of the effect of 

 temperature, oxygen and other factors on the initial part of the fluorescence curve, as- 

 suming that eUmination of the final decay must make the analysis easier. Insofar as 

 these measurements concerned the first wave of fluoi-escence, ABC, they are discussed 

 in sections (c) and (f), because in this part of the induction curve the effects of cyan- 

 ide are minor. Here, we will discuss some results concerning the "second wave." 



18 



UJ 



o 



z 



UJ 



o 

 (/) 



LJ 

 (T 

 O 



ID 



14- 



12 



10 



TIME, min. 



Fig. 33.39. Fluorescence-time relation in air at 29° C. as a function of inhibi- 

 tion of photosynthesis by cyanide (after Wassink and Katz 1939). Per cent 

 KCN shown on curves; 0.1 ml. added to 2 ml. cell suspension. 



Figure 33.39 shows that the decline of photosynthesis after the second maximum is 

 much more sensitive to cyanide than the decline after the first peak. Even 5 X 10"'* 

 per cent cyanide in solution (corresponding to 7.7 X 10~* mole/1.) had a strong effect, 

 while 1.65 X 10"^ per cent (2.6 X 10~' mole /I.) eliminated the decay altogether. This 

 compares with 2% HCN in air, or about 0.15 mole/1, in the equilibrated aqueous phase, 

 which Franck and co-workers found to be the smallest quantity affecting the first wave 

 of fluorescence. The two observations refer to different species, and it was shown in 

 chapter 12 {cf. Table 12. V) that the sensitivity of plants to cyanide varies widely; how- 

 ever, in this case, the variation is so extreme that it can be taken as indicative of differences 

 between the reactions that bring about the fluorescence decay after the first and the 

 second maxima. 



Figure 33.40 and 33.41 show the influence of light intensity and temperature on the 

 ascending slope of the second wave, CD, in cyanide-inhiV)ited Chlorella cells. The sec- 

 ond wave behaves as if it were caused by a combination of a photochemica reaction with 

 at least two thermal reactions. At low intensities, the slope CD is proportional to / and 

 independent of T; at higher intensities, a "saturation" is reached — the lower T, the 

 earlier. At still higher intensities, the rate decreases again (apparently due to the de- 

 velopment of a second minimum, near 1 minute). 



The retarding influence of phenylurethan on fluorescence decay was 

 fir.st observed by Kautsky and Hirscli (1935). Figure 33.42 shows this 



