460 



S. S. Brody and M. Brody 



4. Evidence B ased on Photosynthesis Measurements: The close correla- 

 tion between the onset of photo synthetic efficiency and the shift of the absorp- 

 tion maximum of chlorophyll from 670 to 678 mfx - observed during the 

 "greening" process in etiolated plants (37,50) - is suggestive of the need for 

 aggregated chlorophyll in photosynthesis. While Smith, French, and Koski 

 (50) proposed that the only photochemically active form is the chlorophyll 

 with maximum at 678 m(j., Krasnovsky and Kosobutskaja (37,38) suggested 

 just the opposite possibility. In addition, the latter workers proposed that 

 the band with absorption maximum at 670 m|j. represents the fluorescent, 

 monomeric form while the other, non-active form with maiximum at 678 m(jL, 

 is aggregated and nonfluorescent. They also chose to attribute the spectral 

 shifts in the greening process to formation of aggregates rather than to the 

 formation of chlorophyll-lipoprotein bands. 



It may be recalled that Weber and Teale (59) and Lavorel (43) had 

 attributed the long wavelength decline in yield of fluorescence to the forma- 

 tion of nonfluorescent aggregates. Lavorel had, in addition, suggested that 

 this explanation could also be applied to photosynthesis, i. e. , that the long 

 wavelength decline arose because of photosynthetic inactivity on the part of 

 the nonfluorescent aggregate in vivo . Lavorel's suggestion was in full agree- 

 ment with the observation of his contemporaries on photosynthetic action 

 spectra. However, it has been subsequently shown that when excitation at 

 short wavelengths is coupled with excitation at long wavelengths, full photo- 

 synthetic efficiency may be realized at the longer wavelengths (20,21,22 ) - 

 "Enhancement Effect". 



Based on their fluorescence emission observations- that the proportion 

 of aggregate and monomer varies widely between different organisms- Brody 

 and Brody (5,8, 1 0) proposed that excitation of both nnonomer and aggregate 

 are necessary for photosynthesis and attributed the presence of the long- 

 wavelength decline in photosynthetic activity ("Emerson Effect") to lack of 

 fulfillment of this requirement at the longer wavelengths. They also inter- 

 preted the enhancement effect in terms of cooperative aggregate and 

 monomer action. 



Systematic studies of the action spectrum of the enhancement effect were 

 made by Govindjee and Rabinowitch (32), and Myers and French (46). They 

 show the presence of two photochemically active forms of chlorophyll in vivo , 

 with maxinna at about 670 and 678 na|jL. 



Goedheer (31) has demonstrated that the development of photosynthetic 

 capacity depends not upon concentration of chlorophyll but rather upon forma- 

 tion of the chlorophyll emitting at 720 m(j. (as observed at low temperatures). 

 This supports the hypothesis (5,8) that the aggregated form of chlorophyll is 

 essential for photosynthesis. 



