276 T. W. GOODWIN 



oxygen and the remainder nitrogen, rapidly synthesized bacteriochloro- 

 phyll. Mr. Brian Davies in my laboratory has repeated these experiments 

 using Rhodospirillum rubriim and found the same situation to exist ; further- 

 more he has extended the experiments and has found what one would have 

 anticipated, that spirilloxanthin is synthesized alongside bacteriochloro- 

 phyll. Two possible explanations exist: {a) either a-ketoglutarate and/or 

 fumarate and the carbon residue of glycine are providing carotenoid 

 precursors, or {b) the conditions are such as to stimulate the conversion of 

 an existing precursor into spirilloxanthin. If the latter is the true explana- 

 tion then the precursor must be far back in the biosynthetic pathway 

 because resuspension of colourless R. riibrum cells in the Lascelles medium 

 to which the carotenoid inhibitor diphenylamine has been added, results 

 in the accumulation of the partly saturated polyenes, phytofluene, etc. If 

 the first possibility is correct then compounds other than CO., are actively 

 concerned in carotenogenesis and thus the situation is to some extent 

 dilTerent from that in etiolated leaves. These differences of detail aside, 

 the effect of light on both organisms is essentially the same, and it is hoped 

 that soon a biochemical explanation of this important action of light in 

 controlling terpenoid synthesis in photosynthetic organisms will be forth- 

 coming. I think that vou will agree that this is a key problem because, if 

 this re-routing of terpenoid intermediates on illumination did not occur 

 then functional chloroplasts and chromatophores would not result. 



References 



1. Stanier, R. Y., "The Harvey Lectures" (1958-9) Academic Press, New York, 

 219 (i960). 



2. Goodwin, T. W., "Recent Advances in Biochemistry", London, Churchill 

 (i960). 



3. Goodwin, T. W., Auu. Rev. Plant Physiol (in press) (1961). 



4. Goodwin, T. W., Advanc. Enzy?noL 21, 295 (i959)- 



5. Goodwin, T. W., Biochern.J. 70, 612 (195^)- 



6. Davies, B. H., and Goodwin, T. W., Biachcni.y. 73, loP (1959). 



7. Lascelles, J., Binchnn.'J. 72, 508 (1959). 



