OBSERVATIONS ON THE FUNCTION OF CHLOROPHYLL a 

 AND ACCESSORY PIGMENTS IN PHOTOSYNTHESIS 



David C. Fork 



SUMMARY 



The "inactive" chlorophyll of red algae in red or in blue light 

 was seen when action spectra for photosynthesis were determined at 

 low temperatures but was abolished when action spectra were deter- 

 mined with green background light (absorbed by phycobilins) . En- 

 hancement was thus not limited to the red absorption band of chlo- 

 rophyll a t>ut occurred as well in the blue. 



Enhancement spectra are given for green, brown, and red algae. 

 The results are considered in terms of the Emerson enhancement 

 effect that efficient photosynthesis requires dual excitation of 

 accessory pigments and long -wavelength chlorophyll. 



Two different light reactions, each sensitized by a different 

 pigment system were seen in chloroplasts lacking added Hill oxi- 

 dants. An action spectrum for the Go-production spike had a peak 

 at 669 mii, a far-red limit around 713 m|j, and suggested the func- 

 tioning of the accessory or short-wavelength chlorophyll system, 

 while the action spectrum for the regeneration of the O2 spike by 

 light had a peak near 700 mu which indicated the participation of 

 the long-wavelength chlorophyll system, 



INTRODUCTION 



Until the discovery by Emerson^^^ of what has become known as 

 the enhancement effect of photosynthesis the so-called accessory 

 pigments were considered to function only insofar as they were 

 able to pass along their absorbed light energy to chlorophyll a. 



Red algae presented an apparent exception since Haxo and Blinks 

 (2) found that photosynthesis was efficiently sensitized by phyco- 

 bilin-absorbed light. However, absorption of light by chlorophyll 

 ^ itself resulted in only feeble O2 production. Since fluorores- 

 cence studies by Duysens(3) and French and Young' ^^ indicated that 



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