SPECTRA OF PHOTOSYNTHETIC PIGMENTS 359 



ACTION SPECTRA OF PHOTOSYNTHESIS 



Seventy years ago the participation of a number of pigments as light 

 absorbers in photosynthesis was clearly evident despite the fact that the 

 methods available at that time did not give quantitative results and vari- 

 ous sources of error were not taken into consideration. Englemann 

 (1883, 1884), using motile bacteria for detection of oxygen evolution in 

 red, blue-green, and yellow-brown algae, showed that light of spectral 

 regions other than those absorbed chiefly by chlorophyll was active in 

 photosynthesis. From these results he concluded that other pigments 

 as well as chlorophyll were able to perform this function. Since then a 

 number of workers have confirmed these results, e.g., Montfort (1934, 

 1936, 1941), Ehrke (1932), Schmidt (1937), and Levring (1947), to men- 

 tion but a few. Since most of this type of work was done using broad 

 spectral regions isolated by filters and since much more accurate data are 

 now available, many papers of great significance for their time will not be 

 discussed here. Photosynthesis action spectra have in recent years been 

 obtained for green, red, brown, and blue-green algae using light of narrow 

 band width. Emerson and Lewis used manometric methods for their 

 determinations on Chlorella (1943) and Chroococcus (1942). Haxo and 

 Blinks (1950) developed a polarigraphic method that permits the rapid 

 determination of action spectra over wide ranges of wave lengths with 

 biological variations kept at a minimum. 



Figures 6-7 and 8 show absorption and action spectra of various organ- 

 isms. In all these curves except those for red algae, chlorophyll a partici- 

 pation is evident from the maximum at 678 m/x. 



It is a strange fact that, in spite of the number of papers on the effect 

 of different wave lengths on photosynthesis, we have been unable to find 

 a curve in the literature giving really reliable measurements of the rate of 

 photosynthesis of a leaf of a higher plant at many different narrow wave- 

 length bands. Figure 6-7a does, however, show corresponding action 

 and absorption spectra for chloroplasts. The action measured by Chen 

 (1951) was the reduction of an indophenol dye by a chloroplast suspen- 

 sion. This is one type of "Hill reaction" and is beheved to be carried 

 out by the same chloroplast components that are responsible for the 

 photochemical step of photosynthesis. Part of the action spectrum, 

 unfortuijately one of the most interesting parts, is omitted here because 

 the original data contain a point that appears to deviate from the curve. 

 Chlorophyll b participation is evident from the 655-m^ hump. At 435 m/x 

 the action peak is only 20 per cent lower than the absorption, which may 

 be taken to mean that some of the carotenoids may be functional. Con- 

 siderable inactive absorption is evident, however, from 400 to 430 m/x. 

 The parts of the action curve which rise above the absorption curve may 

 be attributed either to experimental error or to the presence of some 



