360 



David C, Fork 



(54 ergs cm"^ sec"^ at 700 tnn) the peak occurred near 700 np 

 (figure 8). This shift of the peak position in the action spec- 

 trum for light regeneration of the O2 spike may be due to compe- 

 tition between opposing reactions--a promoting reaction driven by 

 far-red light and a depleting reaction resulting in O2 evolution. 

 With higher intensity far-red light some O2 evolution would occur 

 as a result of absorption by the tails of the absorption bands of 

 the short -wave length chlorophylls which extend to the near infra 

 red. 



The action spectrum for the 02-production spike in figure 8, 



600 



650 "700 



Wavelength, iTiM 



750 



Fig. 8, Action spectra (equal incident quanta) for the 

 Oo -production spike in background 700 mp light and for 

 the regeneration of the O2 spike by light. Swiss chard 

 chloroplasts equilibrated without Hill oxidants in the 

 solution given in figure 6. Gas phase, N2. The action 

 spectrum for the regeneration of the spike is plotted 

 above the level of the dark recovery. For this action 

 spectrum the quantum flux at 700 m^ was 54 ergs cm"^ sec"l, 

 The same intensity 700 mp background light was used for 

 the action spectrum of the O2 spike, while the energy of 

 the 669 mp beam was 475 ergs cm-2 sec-^. 



