1402 



INDUCTION PHENOMENA 



CHAP. 33 



"Anaerobic" fluorescence curves of a more complex shape were obtained by Kautsky 

 and Eberlein (1939) and Kautsky and U. Franck (1943) with the green alga Ulva lactuca 

 (cf. fig. 33.45). The incubation time was 100 minutes. A new feature, recognizable in 

 the detailed figure 33.45a, is an inflection on the ascending branch, AB, which may be 

 the first indication of transformation into the "anaerobic" fluorescence curve. (The 

 latter has a maximum at zero time. ) 



No effect of oxygen was observed in Ulva lactuca between 10 and 80% O2; but, al- 

 ready at 1% (at 20° C), the fluorescence wave was noticeably enhanced because of the 

 delay in decay BC, and the initial fluorescence level was much higher than in air. 



TIME, min. 



Fig. 33.46. Fluorescence-time relations in air and N2 at 29° C, with and 

 without cyanide (after Wassink and Katz 1939). 



Experiments on the effect of oxygen on the fluorescence curves of 

 Chlorella were carried out by Wassink and Katz (1939) ; their results (fig. 

 33.46) were quite different from those of Kautsky. In oxygen-free nitro- 

 gen, they found the fluorescence wave to be higher than in air, with decay 

 BC taking more time, but decay DE accelerated. After 1 hour, the differ- 

 ence between the two curves disappeared (probably in consequence of the 

 oxygen production by photosynthesis). A similar family of four curves 

 (air with and without cyanide, and nitrogen with and without cj'^anide) 

 was given by Shiau and Franck, except that, basically, their curves were 

 of type I, while Wassink's curves in figure 33.46 are closer to type II. 

 (For example, in fig. 33.46 the second wave was marked even in the absence 

 of cyanide, while in the curves of Shiau and Franck this wave only ap- 

 peared when cyanide was present.) 



Most of the experiments of Wassink and Katz were carried out under complete 

 inhibition of photosynthesis by cyanide, and consequent absence of the final fluorescence 

 decay; the general shape of the curve was as shown in figure 33.39, and the authors 

 studied the effect of oxygen concentration on maximum B and the second ascent, CD. 

 Both were found to decUne sharply with increase in [O2] up to about 2%, and become 



