FOREWORD 



This volume contains the papers submitted to a synnposium on "Photo- 

 synthetic Mechanisnns of Green Plants," held at Airlie House, Warrenton, 

 Virginia, Oct. 14-18, 1963. The symposium was proposed and sponsored by 

 the Committee on Photobiology , of the National Academy of Sciences— National 

 Research Council, Carl P. Swanson, Chairman. The funds for the symposium 

 were provided by a generous grant from the National Science Foundation, with 

 ancillary support from the Kettering Foundation, Yellow Springs, Ohio. 



It was the feeling of the Committee that progress in the field since the 

 last meeting of this kind, Gatlinburg, 1955, warranted a summing up and 

 organization of our newer information. In retrospect, a brief paper by Blinks 

 in that last meeting proved to be the forerunner of the period in photosynthesis 

 research which we attempted to crystallize at Airlie. Blinks' report on chro- 

 matic transients brought the realization that photosynthesis is not "color 

 blind"— and that different pigments might sensitize different photoprocesses . 

 Soon followed the observation by the late Dr. Emerson of the enhancement 

 effect in which lights of two different wavelengths proved to exert a greater 

 effect if given simultaneously than if given individually. This enhancement of 

 net rate was rationalized by the observation of a push-and-puU effect of two 

 different colors upon intermediate catalysts of the process: i.e. , P700 and 

 cytochrome f . The analysis of photosynthesis in terms of two distinct photo- 

 reactions, their features and their coupling, has consequently been the main 

 area of concentration during the last years. This interest is reflected in a 

 large percentage of the papers in this symposium. Enhancement, transients, 

 and respiratory interactions with at least one light reaction have been studied 

 in great detail. Considerable spectroscopic evidence concerning primary and 

 early events has accumulated. Also on the basis of biochemical studies and 

 analysis using mutants, a picture of photosynthetic electron transport is be- 

 ginning to emerge, albeit somewhat hesitantly. There seems to be fair agree- 

 ment at present about the nature of the first photoreaction, producing an as yet 

 unidentified strong reductant, and a weak oxidant (P700). Compared to this 

 the details of the other photoact and the evolution of oxygen associated with it 

 are still quite obscure. 



Considerable progress is reported in regard to the nature and function 

 of known and newly discovered constituents of the electron transport chain: 

 chloroplast ferredoxin, transhydrogenase, plastoquinones , cytochrome_f , and 

 plastocyanine. Photophosphorylation in chloroplasts , discovered about the 

 time of the previous meeting in Gatlinburg, appears to be far from a finished 

 problem. Some newer aspects are presented here, such as a large pool of 

 high-energy intermediate, capable of inaking ATP in the dark. 



It is interesting to note that probably no area of photosynthesis can yet 

 be considered a closed chapter. Although the path of carbon in photosynthesis 



