CHAPTER 6 



The Absorption, Action, and Fluorescence Spectra 

 of Photosynthetic Pigments in Living Cells and 



in Solutions^ 



C. S. French and Violet ]\I. K. Young 



Department of Plant Biology, Carnegie Institution of Washington, 



Stanford, California 



Introduction. Absorption spectra: Measurement of absorption spectra in scattering 

 media — Absorption and reflection spectra of leaves and algae — Absorption spectra of 

 some purified ehloroplast pigments. Action spectra of photosynthesis. Fluorescence 

 spectra of photosynthetic pigments: Fluorescence spectra of the extracted pigments — 

 Transfer of energy between pigm,ents in live plants as determined by fluorescence spectro- 

 scopy. Spectra of photosynthetic bacteria: Absorption spectra of photosynthetic bacteria 

 and of their pigments — Action spectra of photosynthesis, phototaxis. and fluorescence 

 excitation in purple bacteria. Concluding remarks. References. 



INTRODUCTION 



Most of the pigments of plants that live by photosynthesis have been 

 extracted by organic solvents, then purified and crystallized. Their 

 chemical compositions and reactions are well known, their absorption 

 spectra have been precisely measured, and the photochemical reactions 

 of the most important plant pigment, chlorophyll, have been investigated 

 in solutions of the pure substance. There is, however, a striking contrast 

 between the detailed knowledge of the behavior of the isolated pigments 

 and the great lack of information available on the properties and reactions 

 of these same pigments as they occur and function in living plants. A 

 simple comparison of the absorption spectra of pure chlorophyll solutions 

 with the absorption spectra of leaves or of algae shows at once that in 

 the living system, capable of carrying on photosynthesis, the pigments 

 are very different. The failure of all attempts to reproduce a photo- 

 synthetic system with purified pigments appears to be in part due to the 

 different nature of the intact and the extracted pigments. 



The chemical information about the purified pigments is of great value 

 in identifying and measuring the quantity of the various pigments 



1 Manuscript submitted for publication Dec. 14, 1951; only a few references were 

 added later, although the field has developed appreciably since then. 



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