469 



S. S. Brody and M. Brody 



Now let us return to our observation of emission in the blue-green region 

 of the spectrum, which is especially evident at low temperature (see Figs. 

 8-15). Although this emission is apparent in all the organisms we have 

 examined, only in Euglena is there a clear cut pattern in its appearance. 

 (We did not study this phenonenon in detail in the other organisms, and in 

 Ochromonas we have not been able to get consistent data. ) In young Euglena , 

 in which there is little chlorophyll, emission in the blue-green region is 

 strong. As the cells age and more chlorophyll is formed, there is a corres- 

 ponding decrease in blue-green emission (which may be only relative - 

 although preliminary data suggest there is actually a dimunition in yield). 

 This fluorescence in Euglena was attributed to carotenoids by Brody and 

 Linschitz (12) on the basis of similar emission and action spectra for 

 carotenoids extracted from Euglena with alcohol. It should be noted that 

 Goedheer (31) has attributed fluorescence in this region in greening bean 

 leaves to FMN and DPNH derivatives. 



C. Size of Chlorophyll Aggregates in Vivo 



The marked similarity between the spectral properties of chlorophyll in 

 vivo and aggregates in vitro has already been noted (4,9 ). In this section 

 we assume that, except for the species giving rise to emission at 687 m^i, 

 all of the chlorophyll in vivo is present in the form of molecular aggregates. 

 On this basis, an effective size for the aggregate is estimated from the 

 position of the aggregate emission maximum at 77°K. It is further shown 

 how the size of the aggregate varies with the age of the organism. 



After dark grown Euglena has been in light for several hours, there is 

 noted, in addition to fluorescence from the chlorophyll monomer (maximum 

 687 mp.), a second emission maximum at 717 mjj. (77°K). After Euglena 

 has been in light for still longer periods of time, the position of the long wave- 

 length emission maximum shifts further toward the red end of the spectrum, 

 until - after 80 hours - it reaches 732 mji. The position of the long wave- 

 length emission maximum as a function of time in light is shown in Fig. l6, 

 where a smooth curve has been drawn through the experimental points. 



To estimate the size of the aggregate, an expression derived by McRae and 

 Kasha (45) is used: 



~" -~" = 4(N-l)m^ (1+cos^ a)/NhcR'^ Eq. (1) 



Aj A^ 



N = number of chlorophyll molecules in the aggregate; v ^ and v ^^ ~ 

 absorption maxima of aggregate; o= angle between the axis of the aggregate 

 and the planes of the molecules forming the aggregate; R = distance between 

 charge centers; c = speed of light; h = Planck's constant; m = transition 

 moment. 



In the present analysis, it is assumed that the chajiges in spectroscopic 



