412 THE PIGMENT SYSTEM CHAP. 15 



to 6.4% in the precipitated ''chloroplastic matter" — which he therefore 

 considered as contaminated by 15% cytoplasm (c/. page 369). Smith's 

 analysis (1941) of the same material gave 8% chlorophyll, while Bot 

 (1942) found only 4 to 6% chlorophyll in the dry chloroplastic matter 

 from Latyrus and Spinacia. 



If all chlorophyll is concentrated in the grana, its concentration there 

 must be about twice that in the chloroplast as a whole, and five or six 

 times that in the whole cell, i. e., 10-30% of the dry weight, or 0.06-0.2 

 moles per liter, depending on whether the average concentration in the 

 dry chloroplastic matter is 5 or 15%. The bearing of these figures on 

 the problem of the state of chlorophyll in the chloroplasts was discussed 

 in chapter 14 (page 390). 



C. The Carotenoids* 



Berzehus (1837) made the first attempt to extract the yellow pigment 

 — which he called xanthophyll — from autumnal leaves. He considered 

 it at first as a decomposition product of chlorophyll, but found later 

 (1838) that it exists as such also in summer leaves (as was suspected as 

 early as 1827 by Guibourt, Robinet, and Derheim). Confirmations of 

 this fact were given by Fremy (1860) and Stokes (1864), who fractionated 

 the leaf extracts by means of immiscible solvents. 



Stokes (1864) recognized that the yellow pigment consists of two 

 main constituents. One of them is called carotene because of its identity 

 with the pigment of the carrot. The name xanthophyll was retained 

 for the other. Chemical studies have shown that carotene is a carbo- 

 hydrate which exists in several isomeric forms, while "xanthophyll" is a 

 mixture of several isomeric and homologous alcohols derived from the 

 carotenes. It seems best to call them by the generic name of carotenols 

 (cf. page 471). 



The introduction of chromatographic analysis has been of great help 

 in the separation of carotene and carotenol mixtures. According to 

 Strain (1938), about a dozen of these pigments are regularly present in 

 green leaves, while others are encountered in algae and bacteria. 



The first data on the concentration of the carotenoids in plants were 

 obtained by Willstatter and coworkers (of. Willstatter and Stoll 1913, 

 1918). Some of their results, together with the more recent ones of 

 Seybold and Egle (1938, 1939), are given in table 15.III, which shows 

 the contents in carotene, [c], and carotenols, [x], and the ratios, [x]: [c] 

 and([a]+[b]):([c]+[x]). 



The average ratio of [x]:[c] is between 4 and 6 both in the higher 

 plants and algae (if fucoxanthol is included in the carotenol total). 



* Bibliography, page 434. 



