370 



Kouchkovsky et al 



The existence of an initial connplex (the precursor of oxygen) was also 

 demonstrated and its concentration estimated. This complex might contain 

 plastoquinone, since hexane extraction not only cancels the steady-state oxy- 

 gen evolution of the Hill reaction, but also the burst (although the photoabsorp- 

 tion - or at least that part which is a photo-oxidation - would remain in 

 hexane-extracted chloroplasts ) ^ ^'*'. The oxygen burst, being a primary 

 phenomenon of photosynthesis, the absence of this burst in hexane-extracted 

 chloroplasts is in agreement with Witt's hypothesis that the photochemical 

 act of "system 2" (linked to oxygen evolution) consists in the photoreduction 

 of a plastoquinone ' J^^). 



It was also shown that measurements of oxygen evolved during the Hill 

 reaction have to be corrected for the interfering Mehler and photo-oxidation 

 reactions. Light-induced oxygen absorption was also found with intact Chlor- 

 ella cells, but its mechanism seems to be more complicated' '. 



Employing the proposed mechanisms it has been possible to generate data 

 mathematically similar to those found in our experiments. Some curves, 

 computed in this way, are shown in reference 5. 



Ackno'wledgement 



It is a pleasure to thank here Dr T. T. Bannister for correcting this 

 English manuscript, written by one of us, (Y. K. ), during a visit to the 



Photosynthesis Laboratory, University of Rochester (N. Y. ). 



REFERENCES 



1. Lavorel, J., Plant Physiol . , 34, 204(1959). 



2. Joliot, P., J. Chim. Phys ., 58, 570(1961). 



3. de Kouchkovsky, Y. , Fifth Intern. Congress Biochem. ,Pergamon Press, 

 Oxford (1961), abstract 22-28-2269. 



4. Rabinowitch, E. , in Photosynthesis and Related Processes , Intersci- 

 ence Publ, New York, vol 11-2(1956), p. 1375. 



5. de Kouchkovsky, Y. , Physiol. Veg . , L 15(1963). 



6. de Kouchkovsky, Y. , Compt. Rend. , 248, 3597(1959) and 252, 6 1 1( 196 1). 



7. Fork, D.C., Plant Physiol . , 38, 323(1963). 



8. Mehler, A. H. , Arch. Biochem. Biophys ., 33, 65 and 34, 339(1951). 



9. Briantais, J.-M. , Physiol. V^g. , in press. 



10. Mehler, A. H. and Brown, A. H. , Arch. Biochem. Biophys ., 38, 365 

 (1952). 



11. Avron, M. , Jagendorf, A. T. and Evans, M., Biochim. Biophys . Acta , 

 26, 262(1957). 



12. Allen, M. B. , Whatley, F. R. and Arnon, D. I. , Biochim. Biophys. Acta , 

 27^, 16(1958). 



13. Witt, H. T. , MuUer, A. and Rumberg, B., Nature , 197 , 987(1963). 



14. de Kouchkovsky, Y. , unpublished. 



