45 



FLUORESCENCE STUDIES 



Bessel Kok 



I, A photoinitiated emission at 698 mu ♦ 



Brody and Brody (1) mentioned that upon cooling to 77*'K 

 the 685 mu fluorescence maximum shifts to 69O mu. We ob- 

 served, hov;ever, that the location and intensity of the 685 mu 

 band ("FSS^") are practically independent of temperature. 

 Below -150°C a distinctly separate band develops at 696-698 mu 

 (denoted "F700") which keeps increasing with decreasing tem- 

 perature until in many cases it is the most pronounced emis- 

 sion (cf. Figs. 2, k, and 5). This emission occurs in all 

 organisms we have investigated, in acetone extracted or deter- 

 gent treated chloroplasts, but not in solutions of chlorophyll. 



In fresh chloroplasts, leaves or algae, a striking feature 

 of this emission band is a requirement of light in order to 

 fully develop. Figure 1 (top curve) shows an experiment made 

 in the following way: a sample of chloroplasts was kept in 



i 



E 3 



Figure 1 

 the dark for a few minutes and then cooled to liquid nitrogen 

 temperature — also in darkness. Upon addition of the exciting 

 light, the fluorescence intensity rises instantaneously to a 

 certain level (Eq) and from thereon much more slowly until it 

 reaches a final value (Ejj^ax^* 



An immediate rise of fluorescence is typical for pigment 

 in solution, for most of the low temperature emission at 730 

 mu ("F730") and also for the 685-697 bands in aged or heated 

 chloroplasts. It indicates that already, before light is 



