378 



C.P. l-Jhittingham and P.M. Bishop 



peak at 675 mp; and the second from 690 and beyond to about 705 

 mp, with a peak at 700 mp. There is little or no influence of the 

 background light on the flash from 642 to 670 mp, and between 680 

 and 690 mp. 



The magnitude of the enhancement was found to be slightly 

 greater with a 697 mp flash than with a 644 mp flash. A reduction 

 in the intensity of the background light reduced the peak heights 

 at the enhancing wavelengths, but did not alter their position: 

 this effect was considerably greater with the 697 mp flash than 

 with the 644 mp flash. It seems probable that the use of a higher 

 intensity background light would have increased the absolute peak 

 heights of enhancement obtained with a 697 mp flash. 



When an uncoupling agent was added to ferricyanide it was still 

 possible to obtain an enhanced yield from both flashes, by the use 

 of background light. The yield from the 697 mp flash was increas- 

 ed 707. with a background of 653 mp, and that of a 644 mp flash 

 40% with the addition of a 700 mp background. 



With TPIP alone, at the concentration used in the white light 

 flash work reported above, there appeared to be no effect of back- 

 ground light on the yield of either of the flashes. However, a 

 reduction in the concentration of the dye from 3 x 10~^M to 5 x 

 lO'^M, resulted in an increase in yield of 557. from a 697 mp flash 

 with a 653 mp background; with a 675 mp background the effect 

 could not be established as significant. No increase was obtained 

 with a 644 mji flash, and when this v/as superimposed on a 700 mp 

 background, of the same intensity as normally used, a reduction 

 in the yield occurred, compared to the flash without background 

 light. This inhibitory effect could be eliminated by a reduction 

 in the intensity of the 700 mp illumination. 



The data thus show that it is possible to enhance the oxygen 

 yield from a flash of light by the addition of supplementary light 

 of certain wavelengths. The extent of the enhancement obtainable 

 depends on the oxidant the chloroplasts are reducing. With ferri- 

 cyanide, the output from a 697 and a 644 mp flash can both be in- 

 creased; the marked dependence of the enhancement on the wave- 

 length of the background light indicates the presence of different 

 forms of chlorophyll with sharp absorption bands. ;>Jhen an un- 

 coupling agent is added to ferricyanide, it is still possible to 

 enhance the yield from both flashes in conjunction with back- 

 ground wavelengths found to be effective with ferricyanide alone. 

 With TPIP as oxidant, however, it is only possible to enhance the 

 yield from the long wavelength flash; there is some indication 



