CHAPTER 3 



THE CHEMISTRY OF PIGMENTS ASSOCIATED 

 WITH THE CHLOROPLAST 



The pigments of the chloroplast belong to two chemical 

 classes; tetrapyrrolic compounds, to which class chlorophyll 

 belongs, and the carotenoids which include the yellow xan- 

 thophylls and the orange carotenes. The colour of leaves 

 may be modified by the presence of other pigments, the red 

 or purple anthocyanins, but these are dissolved in the cell 

 sap and are absent from the cytoplasm. The anthocyanins 

 play no direct part in photosynthesis. In the red algae 

 additional pigments which often mask the green colour of 

 the chlorophyll are present and intimately associated with 

 the chloroplasts. These are chemically related to the chloro- 

 phylls, and are tetrapyrrolic compounds. The light ab- 

 sorbed by them can be used in photosynthesis. 



THE CHLOROPHYLLS 



The chlorophylls are reaaily extracted from fresh green 

 tissues of plants by acetone and from powdered dried leaves 

 by both acetone and alcohol. It is necessary in the latter case 

 to add water to the extent of lo to 20% or extraction is in- 

 complete. The pigments may be separated by differential 

 distribution between immiscible solvents or by fractional 

 absorption. Willstatter and Stoll (1913) should be consulted 

 for details of this and other procedures. The first method, 

 used by Willstatter, proceeds by adding the acetone extract 

 to an equal volume of petrol ether and a little water. The 

 petrol ether separates containing almost all the chlorophyll. 

 Most of the xanthophyll and some chlorophyll h is removed 

 by shaking with aqueous methanol. By repeated washing 

 with water the petrol ether solution loses its fluorescence and 

 the chlorophyll begins to come out of solution. It can then 

 be obtained by filtering through a thin layer of talc and the 



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