430 



THE PIGMENT SYSTEM 



CHAP. 15 



that lower plants (up to the Bryophyta) are capable of synthesizing 

 chlorophyll without the help of light. Myers (1940) found no difference 

 between the composition and photosynthetic efficiency of the pigments 

 formed by Protococcus and Chlorella in darkness and in light. The 

 capacity for chlorophyll synthesis in the dark extends also to conifers 

 (see, for example, Lubimenko 1928, and Seybold and Egle 1938), although 

 light accelerates the formation of chlorophyll in them, as is illustrated by 



table 15.XI. 



Table 15.XI 



Rate of Greening (after Lubimenko) 



The rate of formation of chlorophyll depends not only on the intensity 

 of light, but also on its spectral composition. Emerson and Arnold 

 (1932) and Emerson, Green and Webb (1940) used light of different 

 color to effect the growth of Chlorella cells with varying contents of 

 chlorophyll. According to Sayre (1928), Rudolph (1934), Seybold and 

 Egle (19380, Simonis (1938), and Strott (1938), the synthesis of chloro- 

 phyll occurs in red light more rapidly than in blue or green light of the 

 same intensity. This phenomenon deserves a closer study. The higher 

 efficiency of red light may be due to its absorption by a chlorophyll 

 precursor, or it may be the result of an "autosensitization" by the 

 reaction product (chlorophyll), i. e., to a photochemical counterpart to 

 autocatalysis. 



Johnston (1932) found less chlorophyll in plants grown in red light; Lease and 

 Tottingham (1935) noted that the chlorophyll production increased when blue-violet 

 light was added to red light; and Stoklasa (1915) asserted that the formation of chloro- 

 phyll occurs more rapidly in ultraviolet light than in visible sunlight. 



Lubimenko and Hubbenet (1932) have studied the effect of tempera- 

 ture on the rate of formation of chlorophyll, and have found a tenfold 

 increase between 5° and 15° C, and an increase by a factor of 1.5-2 

 between 18° and 28°. They associated this influence of temperature 

 with the enzymatic transformation of leucochlorophyll into chlorophyllo- 

 gen (c/. page 404). 



The development of carotenoids is also affected by light. According 

 to Strain (1938), seeds contain almost no carotene but several carotenols. 

 On the other hand, Seybold and Egle (1938) found both carotene and 



