CHLOROPHYLL FORMATION 



410 



Temperature affects the formation of both chlorophylls a and b and to 

 approximately the same extent. In Fig. 7-17 are shown the rates of for- 

 mation of chlorophylls a and b in barley seedlings at 4.2° and 17.1°C. 

 Although the absolute rates of formation are greatly affected by temper- 

 ature, the relative rates of formation of chlorophylls a and b remain 

 nearly constant over a considerable range of chlorophyll concentrations 

 and are approximately the same for different temperatures, as shown in 

 Fig. 7-18 (see also Seybold and Egle, 1938; Blaauw-Jansen et al., 1950). 



There is an optimum temperature for the accumulation of chlorophyll, 

 as Lubimenko and Hubbenet (1932) have clearly shown (Fig. 7-19). 



Fig. 7-18. The relation between the accumulation of chlorophjdls a and b at different 

 temperatures under continuous and intermittent illumination of dark-grown barley 

 seedlings. The numbers adjacent to the lines designate their slopes. {Smith, 1949b.) 



From the graph it is seen that the optimum temperature is about 27°C 

 for wheat seedlings {Triticum ferrugineum). The range of temperature 

 for this plant which permits chlorophyll accumulation is from 3° to 48°C. 

 Plants heated at 47°C for 48 and 72 hr died. Strain (1938, p. 124) found 

 that immersion of barley seedlings in water at 50°C for 30 sec inhibited 

 chlorophyll formation. Different plants have different optimal temper- 

 atures for chlorophyll formation (Wiesner, 1877). 



Inman (1940) observed that certain algae that grow in hot springs at 

 temperatures of 37°-72°C retain their chlorophyll. The ratio of chloro- 

 phyll a to chlorophyll b is greater than is commonly found in most plants. 



In contrast to the great dependence of the accumulation of chlorophyll 

 on temperature, the transformation of protochlorophyll to chlorophyll is 

 quite independent of temperature (Lubimenko, 1928). Liro observed 

 that chlorophyll was formed in illuminated etiolated seedlings at temper- 

 atures as low as — 15°C. Scharfnagel (1931) obtained chlorophyll for- 



