343 



C. S. French 



flash, however, remains the same with and without the red back- 

 ground. 



On the other hand, the red flashes behave differently. The 

 height of the spikes from red flashes does not increase when a 

 green continuous background is given. In this case the enhance- 

 ment shows up as a prolongation of the time of O2 evolution fol- 

 lowing the flash. For flashes of either color more O2 is produced 

 per flash when the other pigment system is illuminated by continu- 

 ous light, but the kinetic nature of the increase contrasts sharp- 

 ly. Similar experiments were carried out last summer by the 

 Govindjees in far more detail. 



So far only a beginning has been made in developing a kinetic 

 picture of the relations between the two light reactions of photo- 

 synthesis with their associated dark reactions, as measured by O2 

 evolution, 



COMMENTS ON ABSORPTION AND ACTION SPECTRA WITH PEAKS NEAR 700 m\J 



One of the current basic questions is whether or not all action 

 spectra giving peaks near 700 mn can be explained on the basis of 

 an activity of C^ 685 which is driven in the opposite direction by 

 the overlapping absorption of C^ 650 and Cg 670. If not, there 

 must be three rather than two separate photochemical reactions in 

 the photosynthetic process. The work of the Witt group(21) has 

 lead them to this conclusion. 



Near 700 mn and beyond, the absorption of C^ 685 greatly pre- 

 dominates over the absorption by the tails of the accessory pig- 

 ment system components C^ 650 and C^ 670. Effects due to Cg 685 

 absorption which are reversed by action of the accessory pigment 

 system should therefore give an apparent action spectrum peaking 

 at or beyond 700 mn. 



REFERENCES 



1. Blinks, L. R. , and R. K. Skow, Proc. Nat. Acad. Sci. U.S.A. 



24, 420-427 (1938) 



2. Haxo, F. T., and L. R. Blinks, J. Gen. Physiol, 33, 389-422 



(1950) 



3. Fork, D. C. , Plant Physiol. 38, 323-332 (1963) 



4. French, C. S. , and D. C. Fork, Biophys . J. 1, 670-680 (1961) 



5. French, C. S. , and D. C. Fork, Proc. Fifth Int. Cong. Biochem. 



Vol, VI, 122-137 (Pergamon Press, New York, 1963) 



