CHLOROPHYLL FORMATION 403 



Because protochlorophyll occurs in much higher concentration and is 

 transformed much more slowly in the inner seed coats of certain cucurbits 

 than in etiolated leaves, it is easier to determine the positions of the 

 absorption maxima in the seed coats. Accordingly Monteverde and 

 Lubimenko (1911) have reported the following absorption bands in the 

 seed coats of certain Cucurbitaceae seeds: 



650—640 (620); 600—570; 550—530; 510— E.A. m^. 



Krasnovskii and Voinovskaya (1949) have found the principal absorp- 

 tion band to lie between 650 and 645 m^u in pumpkin seed coats. 



Monteverde and Lubimenko (1911) examined the seed coats of Luffa. 

 The positions of the bands differed in the outer and inner seed coats: 



Outer seed coat, 680-660; 610—590; 570—550; 510—480; 450— E.A. 



m/i. 

 Inner seed coat, 650—640—620; 600—570; 550—530; 510— E.A. ran. 



Extracts of the two gave the same absorption spectrum, which was char- 

 acteristic of protochlorophyll. When heated, the color of the outer seed 

 coats was changed from brown to green. Lubimenko (1928) compared 

 the absorption bands of the Luffa seed coats with those of alcoholic 

 extracts of the same: 



Seed coats, 680-660; 610—590; 570—550; 510—480; 450— E.A. m/z. 

 Alcoholic extracts, 640—620; 590—570; 540—525; 470— E.A. vay.. 



The fact that the positions of the absorption bands in the seed coats 

 vary in different samples, whereas in the extracts of the same they agree 

 with those of protochlorophyll, indicates that the different tissues con- 

 tain different protochlorophyll holochromes. 



The absorption curves for protochlorophyll in various solvents have 

 been obtained by Rudolph (1934), Seybold and Egle (1939), Koski and 

 Smith (1948), Seybold (1948-1949), and Krasnovskii and Voinovskaya 

 (1949). Only the determinations of Koski and Smith are on an absolute- 

 weight basis and for purified protochlorophyll from etiolated leaves (Fig. 

 7-4). The results of Seybold (1948-1949) purport to show the presence 

 of protochlorophylls a and b in pumpkin seed coats. The existence of 

 protochlorophyll b is questionable, since other investigators have failed 

 to find it either in seed coats (Noack, 1934; Fischer and Oestreicher, 

 1939-1940; Krasnovskii and Voinovskaya, 1949) or in etiolated leaves 

 (Koski and Smith, 1948). 



The absorption curves for protochlorophyll in ether, acetone, and 

 methanol are given in Fig. 7-4 (Koski and Smith, 1948). The proto- 

 chlorophyll used was obtained from barley leaves. It was prepared in 

 pure solid form and was weighed directly into the solvents for the 

 absorption-spectra measurements. 



