CHLOROPHYLL FORMATION 425 



Trebitz (1905) found that alcohol and ether vapors that were not injurious 

 to the plant did not inhibit chlorophyll formation except in one plant, 

 Pisum sativum. Liro (1908) observed that seedlings of barley, oats, and 

 wheat, after a half -hour treatment with higher concentrations of ether and 

 chloroform vapor, turned completely white when illuminated. Neither 

 protochlorophyll nor chlorophyll could be detected in alcoholic extracts 

 of these seedlings. vScharfnagel (1931) reported that narcosis brought 

 about with various amounts of ether produced only a negligible inhi- 

 bition of the protochlorophyll-chlorophyll transformation in corn seed- 

 lings. Brebion (1950) related the inhibiting action of various substances 

 to their thermodynamic activities, i.e., for vapors, the fraction of their 

 full vapor pressure which causes inhibition. For the inhibiting activities 

 on chlorophyll formation in wheat seedlings, he gives the following values: 

 ether, 0.35 ; acetone, 0.2 ; benzene 0.2 ; and phenol, 0.06. Brebion has also 

 observed that substances that inhibit chlorophyll formation at one con- 

 centration may stimulate it at a lower concentration. He has given the 

 ratios of inhibitory action to stimulatory action for various compounds. 

 Strain [cf. Spoehr et al. (1938 1939)] has reported the inhibitory action 

 of hydroquinone on the greening of barley seedlings. 



Treatment of barley seeds with streptomycin previous to germination 

 inhibited chlorophyll production in the seedlings (Euler, 1947, 1950). 

 Euler ascribed the action to a deleterious effect on chloroplast formation 

 (Euler and Heller, 1949) and to an obstruction of porphyrin synthesis 

 (Euler, 1950). Cells of Euglena gracilis are bleached in the light when 

 treated with streptomycin (Provasoli et al., 1948). The bleaching is pro- 

 portional to the extent of the treatment. Microscopic examination 

 revealed drastic reduction in the number of chloroplasts. Completely 

 bleached cells never recovered their ability to form chlorophyll. Bogorad 

 (1950b) observed that seeds of Pinus jeffreyi when germinated in the dark 

 on agar containing 0.2 per cent streptomycin produced seedlings with 

 colorless cotyledons in contrast to the green cotyledons produced under 

 normal conditions. When the colorless seedlings were exposed to light, 

 they became green. 



Another compound that, in very low concentrations, adversely affects 

 the formation of chlorophyll is 3-(Q!-imino-ethyl)-5-methyl-tetronic acid 

 (Alamercery et al., 1951). 



Sugars may act as inhibitors of chlorophyll production in certain organ- 

 isms. Kufferath (1913) obtained chlorotic cells of Chlorella luteo-viridis 

 when they were illuminated and grown on an agar medium containing 

 glucose or galactose (1 per cent) or sucrose (2 per cent). Beijerinck 

 (1904) saw that C. variegata had a great tendency to produce chlorotic 

 cells when cultivated on agar plates that w^ere relatively rich in organic 

 carbon sources such as sugar. When only inorganic carbon sources were 

 available, the cultures remained green when illuminated. 



