324 



Govindjee 



E = "1.2 - ^■'l,!' - V (2) 

 "2 



where the symbols have the same meaning as in equation (1), 

 except that R]^', is the rate due to the second (supplementary 

 beam) alone, the intensity of the latter being adjusted so as 

 to give the same rate as that of R„. 



III. ENHANCEMENT EFFECT AND THE TWO PHOTOCHEMICAL SYSTEMS 

 A. Action Spectra . 



The action spectra of the enhancement effect, measured with 

 a background of far-red light, led to the identification of pig- 

 ments present in one of the two postulated phoLosystems 

 (system II). Of course, these action spectra do not; follow the 

 true absorption curves, but rather the"f ractional-absorption" 

 curve of the pigments belonging to system II. Similarly, the 

 action spectra obtained in the presence of background light of 

 shorter wavelength, suggest the fractional absorption curve of 

 pigments in system I. From our previous studiesS, we concluded 

 that system II in diatoms and green algae includes the short- 

 wave form of chlorophyll a (Chi a 670). (See figure 5 for the 

 absorption spectrum55 of Chlorella , showing bands corresponding 

 to the two forms of chlorophyll a). Light energy absorbed by 

 chlorophyll b is assumed to be transferred to Chi a 670. System 

 I is mainly composed of the long-wave forms of chlorophyll a 

 (Chi a 680/Chl a 690 and "Chi a 700"). In figure 6, the solid 

 curve refers to the action spectrum of the enhancement effect in 

 the presence of 700 m|a background light, suggesting the ident- 

 ification of chlorophyll b and Chi a 670 as components of system 

 II. The dashed curve refers to measurements in the presence of 

 650 mil background light. The ratio of the rate due to far-red 

 light to that due to supplementary light is kept constant (1:2). 

 Unlike Myers and Graham^^'^, we observed enhancement of 650 m|j. 

 action by 670 m|a light. It, thus, appears that Chi a 670 occurs 

 in both systems. On the other hand, the long-wave chlorophyll a 

 forms belong exclusively to system I; while chlorophyll b belongs 

 exclusively to system II. 



Soret bands . ForkHias shown that, in red algae, in the action 

 spectrum of enhancement with a background of green light, system 

 I exhibited a Soret band. This was confirmed by Blinks. 15 The 

 demonstration of this band in green algae and diatoms has not met 

 with success in our hands, perhaps due to a strong overlap of ab- 



