VARIATIONS OF CHLOROPHYLL FLUORESCENCE 819 



Seybold and Egle, on the other hand, had to attribute the fluorescence 

 bands to the fraction of chlorophyll dissolved in a lipide, and the absorp- 

 tion bands to the bulk of chlorophyll present in a protein-bound colloidal 

 state. Therefore their theory was predicated on the contention that the 

 fluorescence band of chlorophyll is shifted in lipides toward the longer 

 waves much more strongly than the corresponding absorption band. This 

 hypothesis was characterized as implausible on page 746. 



To sum up, there seems to be no reason to attribute the fluorescence of 

 living plants to a small fraction of chlorophyll molecules, present in a 

 strongly fluorescent solution, rather than to the whole mass of the pigment 

 forming a weakly fluorescent complex with proteins and lipides (including 

 the carotenoids) . The close relationship between fluorescence intensity and 

 rate of photosynthesis, which will be discussed in the next section, also 

 indicates that fluorescence is a property not of a small fraction but of the 

 bulk of chlorophyll in the cell. 



4. Variations of Chlorophyll Fluorescence Related to Photosynthesis 



In the preceding section, we discussed chlorophyll fluorescence in vivo 

 in relation to what may be called the gross state of the green pigment in the 

 living cell — its high concentration and its simultaneous association, in the 

 "chloroplastin," \\ith proteins and lipides. The effects of drying, heating, 

 boiling or immersion in ether, described in that section, can be assumed to 

 be indicative of a partial or complete disintegration of the chloroplastin. 



In the present section, we will deal with reversible changes in the yield 

 of fluorescence that are more or less closely associated with photosensitizing 

 activity and can be assumed to occur without essential changes in the com- 

 position and structure of chloroplastin. 



Kautsky discovered in 1931 that rapid changes in the intensity of 

 fluorescence of leaves occur during the first seconds and minutes of illum- 

 ination after a period of darkness, and bear definite relation to the pre- 

 viously known changes of the rate of photosynthesis during this "induc- 

 tion period." Subsequent investigations by Kautsky and co-workers 

 (1931-1948), Franck and co-workers (1934-1949), McAhster and Myers 

 (1940) and of the Dutch group of investigators (Ornstein, Wassink, Katz, 

 Dorrestein et al. (1937-1949) have revealed many striking examples of close 

 interrelation between the intensity of fluorescence and the momentary 

 rate of photosynthesis. This relationship can be observed not only dur- 

 ing the induction period, but also in the steady state. Factors such as 

 light intensity, temperature, concentration of reactants that take part in 

 photosynthesis, presence of oxygen and various poisons and narcotics 

 are found to affect significantly the yields of both fluorescence and photo- 

 S3m thesis. 



The close interrelation of the fluorescence of chlorophyll and its photo- 



