327 



Govind jee 



IV. 



ENHANCEMENT EFFECTS IN CHLOROPLAST REACTIONS 



We have consistently observed the enhancement phenomenon in 

 the Hill reaction with isolated chlOroplasts , using quinone23 and 

 NADp2'^ as oxidants. These experiments clearly show the existence 

 of an enhancement when a far-red beam is supplemented by light of 

 a shorter wavelength. The action spectrum of this effect has 

 peaks at 650 mjj. (due to chlorophyll b) and 675 m\i (due to chloro- 

 phyll a). (See figures 9 and 10). Enhancement of NADP reduction 

 was acc^ompanied by enhancement of oxygen evolution. The situation 

 may be different with other Hill oxidants, such as certain dyes, 

 or f erricyanide. 



SPfNACM 

 NflOP REDUCTION 



LIGHT INTENSITY IN AReiTRART UNITS 



630 640 650 660 670 680 690 700 



WAVELELENGTH.mx 



Figure 9. Enhancement in NADP reduction as a 

 function of 650 m. light intensity in spinach 

 chluroplasts. (after R. Guvindjee and Govindjee 

 and Hoch). 



Figure 10 Action spectrum of Emerson enhance- 

 ment effect in NADP reduction for spinach chlor- 

 oplasts. (after Yang and Govindjee). 



V. 



FLUORESCENCE STUDIES 



We reported32 ^-t^^^^ the 685 va\x fluorescence excited by 436 m\x 

 light is quenched by the addition of 700 m^ light. This effect 

 can be interpreted in terms of two photochemical systems. 

 Butler33^ Duysens and Sweers^^ obtained similar results. To 

 clarify the mode of action of different oxidants by observing 



