ILLUMINATION DEPENDENCE OF ENHANCEMENT 

 T. T. Bannister and M. J. Vrooman 



The subject of this paper is the dependence of enhancement in 

 Chlorella pyrenoidosa str. 3, on short-wave (U82 mp) and far-red 

 (696 mp) illuminations. Two enhancement functions were deter- 

 mined, the enhancement (E) and the excess rate (D): 



E = (Pi2-Pi)/P2 (1) 



D = P12-P1-P2 (2) 



Here p-, , p , and p-ig ^^^ "the steady state photosynthesis rates in 

 short-wave, far-red, and in the two lights, respectively. To fa- 

 cilitate reference to illumination curves of photosynthesis, p-, , 

 ^2> P-ip ^^^ ^ were expressed as rates relative to the saturated 

 rate in white light. The observed functions E(l2_, I2) and 

 D(l2_, I2) were compared with these predicted by the "spill-over" 

 and "separately packaged pigment" models of enhancement. The pre- 

 dicted functions, which are the same for both models, explain 

 many, but not aJ.1, characteristics of the observed functions. 



METHODS 



Oxygen evolution rates were measured with a horizontal plat- 

 inum electrode similar to that of Myers and Graham ^-^K The plat- 

 inum surface on which the cells were sedimented lay about 0.5inm 

 below a dialysis membrane which separated the electrode com- 

 partment from an external solution containing 0.1 M KCl, O.O5 M 

 phosphate buffer - pH 7-0, 0.01 M KNO3, and O.OO6 M MgSO.. The 

 solution was equilibrated with 1^ oxygen, 5^ CO2 in nitrogen and 

 kept at 22-25 degrees C. 



Interference filters (peak transmission 80^, bandwidths 15 and 

 30 m^ at UO^ and 1^ transmission, respectively) and heat-ab- 

 sorbing filters isolated the monochromatic beams from 1000 watt 

 tungsten lamps. Identical, coincident, homogeneous beams fell 

 either on the electrode or on a thermopile . 



After mounting on the electrode, cells were equilibrated and 



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