1766 CHEMISTRY OF CHLOROPLAST PIGMENTS CHAP. 37B 



Krasnovsky and Kosobutskaya (1953) observed that when etiolated 

 leaves (or plastid fragments from them) were exposed to light the forma- 

 tion of chlorophyll occurred in two stages. In the first 2-3 hours, the ab- 

 sorption peak was at 670 m^i, and most of the chlorophyll formed was easily 

 bleachable by strong light. Later, the band peak gradually shifted to 

 678 m^, and most of chlorophyll became photostable. 



As mentioned above, the development of chlorophyll b in etiolated barley 

 occurs, according to Smith, only in the second, slow stage that follows the 

 initial rapid conversion of preformed protochlorophyll into chlorophyll a. 

 It is possible, but not certain, that the synthesis of the h component in- 

 volves a ''protochlorophyll 6." Such a compound does not accumulate in 

 etiolated seedhngs; but according to Seybold and Egle (c/. pp. 404 and 619) 

 it is present in pumpkin seeds. It is very unlikely that chlorophyll b is 

 formed by oxidation of chlorophyll a. 



The delayed formation of chlorophyll b was noted also by Goodwin and 

 Owens (1947) in oat seedlings. 



The appearance of chlorophyll b is not essentia] for the beginning of 

 photosynthesis, according to Smith (1954). 



Some x-ray mutants of barley were found to be permanently deficient 

 in chlorophyll b (Highkin 1950), but capable of photosynthesis. In some 

 mutants of corn, chlorophyll b was formed only after a delay of from 4 to 14 

 days, depending on temperature (Schwartz 1949). 



Certain x-ray mutants of Chlorella, obtained by Granick (1951), pro- 

 duced chlorophyll only in light (similarly to the higher plants, but unlike 

 normal algae). Granick suggested that the enzymatic system capable of 

 reducing protochlorophyll to chlorophyll in the dark was absent in these 

 mutants. 



The effect of narcotics and of colchicine on the synthesis of chlorophyll 

 in etiolated wheat seedlings was studied by Brebion (1948, 1950). Ether, 

 acetone, benzene and phenol vapors were found to delay the greening in 

 high concentrations and to stimulate it in low concentrations (with 

 phenol, as low as 1 X 10"^%). 



Among new observations of the influence of different external factors 

 on the development of chlorophyll, we can mention the specific effect of 

 streptomycin, first noted by von Euler, Bracco and Heller (1948). Seeds 

 germinating on paper wetted with streptomycin solution developed com- 

 pletely colorless coleoptiles and first leaves. Streptomycin had no effect 

 on leaves already containing chlorophyll. Provasoli and co-workers (1948, 

 1951) found that streptomycin causes Euglena gracilis cells to lose their 

 capacity for forming chloroplasts ; this deficiency was inherited by their 

 offspring. 



Bogorad (1950) noted that the cotyledons of a pine (Pinus Jeffryi), 

 which normally can form chlorophyll in the dark, will do it only in light if 



