302 



Jack Myers 



One of tj-e first concerns in the study of enhancement was the 

 character of pigment systems 1 and 2 or, experimentally, spectra 

 of the enhancement phenomenon. A comparative approach was possi 

 ble because of availability of algal groups with diverse pigment 

 complements. While the exploration has not been completed, it is 

 possible to anticipate two general results. (l) In any one alga 

 there are two spectral regions >v.i and '^2- A combination of wave- 

 lengths chosen between the two will show enhancement. A combina- 

 tion of wavelengths within either region will not show enhance- 

 ment. """^^^^ (The latter statement is recognized as in conflict 

 with certain data.^'"'"^) (s) E>v"en without precise data on in vivo 

 absorption, qualitative conclusions can be drawn from the spectra 

 of A-i and >^2 about the character of pigment systems 1 and 2. Sys- 

 tem 2 is associated with high absorption of accessory pigments 

 phycoerythrin, phycocyanin, fucoxanthin, chlorophyll b, and the 

 special in vivo chlorophyll a-673.^^®'^' "'""'' System 1 is associated 

 with the bulk of chlorophyll a. There is uncertainty about the 

 role of carotenoidSk. The salient features of these conclusions 

 were foreseen by Emerson in his speculations on the role of acces- 

 sory pigments.^ 



EXPERIMENTAL DIFFICULTIES 



Study of enhancement has been complicated by experimental dif- 

 ficulties. Use of narrow bands of monochromatic light places in- 

 creased demands on sensitivity and precision of measuring photo- 

 synthesis. Even as used by Emerson and co-workers the Warburg 

 method is marginal in sensitivity. The bare platinum electrode 

 developed by Blinks and Haxo''"^ provides adequate sensitivity and 

 rapidity but measures only relative changes in net rate of oxygen 

 evolution and has its own special limitations.''"®'^^ The mass 

 spectrometer can provide unequivocal measurement but requires con- 

 siderable calculations to find readout results. ® 



Further experimental difficulties arise from even minor non- 

 linearities in light intensity curves at either of the wavelengths 

 used. One of these is the Kok effect which will be discussed 

 later. A second kind of nonlinearity can be introduced by ap- 

 proach to light saturation.''" 



Coimnent should be made on the special question of whether the 

 enhancement phenomenon is in any way related to differences in 

 light -saturated rate of photosynthesis at different wavelengths as 

 reported by McLeod^^ for Chlorella. Our attempts to confirm these 

 results so far have been uniformly negative.^"^ We have found spe- 

 cial experimental problems but no simple explanation of the differ- 

 ences between our results and McLeod's. However, we do not now 



