1378 



INDUCTION PHENOMENA 



CHAP. 33 



A sequence of three above-suggested processes is suggested also by the 

 common shape of the fluorescence versus time curves found under 

 aerobic conditions, which is shown in figures 33.19a and b. The fluorescence 

 starts at the normal level, A, rises rapidly to a maximum, B (reached about 

 1 sec. after the beginning of illumination), and declines again to the initial 

 level, CD, in about 1 min. These fluorescence curves are mirror images of 

 the typical gas exchange induction curves (fig. 33.19a). Often, however, 

 fluorescence measurements have led to induction curves of a somewhat dif- 

 ferent type, shown in figure 33.20. Here, the "first wave" of fluorescence, B, 

 is low and decays very rapidly, and the induction picture is dominated by a 

 second wave, D, the maximum of which occurs from 3^^ to several minutes 



TIME, min. 



Fig. 33.20. Fluorescence curves of Chlorella with dominant second wave (after Wassink 

 and Katz 1939). Buffer No. 9, 29° C, / = 1 X 10^ erg/cm.» sec. 



after the beginning of the light period. This wave appears to be related 

 to the second depression of the gas exchange, although the latter has been 

 usually encountered above only as a relatively minor disturbance, and not 

 a dominant feature of induction curves (c/. figs. 33.10, 11, 13A,B,F,G). 

 Apparently, the transformation of the photosynthetic mechanism that 

 gives rise to the second wave of fluorescence does not always affect the gas 

 exchange equally strongly, and may sometimes have no influence on this ex- 

 change at all. Thus, while in fig. 33.21(B) the second wave of fluorescence 

 coincides with a distinct depression in the curve of carbon dioxide absorp- 

 tion, no such correlation is apparent in figure 33.22(C): the second wave 

 of fluorescence (which appears here about 0.5 minute after the beginning of 

 illumination, and does not decay until sometime beyond 4 minutes), does 

 not interrupt the steady increase of carbon dioxide consumption. As a 

 result, the fluorescence curve and the carbon dioxide absorption curve as- 

 sume a parallel, instead of the usual antiparallel, course. 



Fluorescence measurements have shown that each of the two waves 

 of fluorescence may possess a "fine structure," with features that reappear 

 with remarkable persistence in curves obtained by different observers with 

 different species. One such feature is a depression on the ascending part 

 of the first wave, noticeable in figure 33.19b, and seen in more detail in 



