ACTION OF TWO-PIGMENT SYSTEM ON 

 FLUORESCENCE YIELD OF CHLOROPHYLL A 



W. L. Butler and N. I. Bishop 



Light-induced fluorescence yield changes of chlorophyll a in 

 vivo have been related to the two-pigment system of photosynthe- 

 sisT Govindjee, et al./^-' reported that the intensity of flu- 

 orescence emitted by chlorella, when illuminated with 67O- and 

 700-nm light simultaneously, was less than the sum of the inten- 

 sities obtained with the 67O- and 700-nm beams separately. 

 Butler (2) showed that the yield of chlorophyll a in vivo was re- 

 versibly increased by irradiation with red light and decreased by 

 irradiation with far red. The action spectrum for the effect of 

 far-red light in decreasing the fluorescence yield had a maximum 

 at 705 nm w ) which was similar to the action spectra for the 

 effects of long-wavelength light in enhancement phenomena of the 

 second Emerson effect. Teale ^^^ reported that with green algae 

 and chloroplasts the action spectrum for the effect of light in 

 increasing the fluorescence yield had maxima at ij.70 and 6^0 nm 

 and a shoulder at 67O nm, a typical action spectrum for the ,. 

 shorter wavelength pigment system in green plants. Duysens^-'' ' 

 also showed with red, blue-green and green algae that the fluor- 

 escence yield of chlorophyll a was increased by light absorbfd 

 by the shorter wavelength pigment system (which he called system 

 2) and decreased by the longer wavelength pigment system (system 

 1). We have also measured the action spectrum for the light- 

 induced fluorescence yield increase in green leaves and algae and 

 will report the results in the present paper. 



The symbolism and theoretical framework introduced by Duysens 

 v5jO) ^11 be adopted in this paper. It will be assumed that 

 pigment systems 1 and 2 both contained chlorophyll a and the 

 accessory pigments (chlorophyll b in green plants and phycobil- 

 ins in red and blue-green algae) but that most of the accessory 

 pigment is associated with system 2. Also, according to Duysens, 

 the chlorophyll a in system 1 is weakly or nonf luorescent, while 

 the chlorophyll a in system 2 fluoresces with a variable yield 

 that depends on the redox state of a quenching substance Q. A 

 similar quenching substance was proposed by Kautsky, et al. ^ '•' 

 on the basis of a detailed kinetic analysis of fluorescence 



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