SECRETARY'S REPORT 95 



subsequent irradiation. However, a pretreatment with red energy of 

 delta amino levulinic acid infiltrated leaves did not increase chloro- 

 phyll synthesis, and beyond an hour of irradiation at low intensities, 

 the rate of chlorophyll synthesis declined. At high intensities, the 

 newly synthesized chlorophyll is destroyed. 



The regulation of chlorophyll formation and the development of 

 the photosynthetic apparatus as affected by inliibitors of protein syn- 

 thesis were studied. Chlorophyll formation was inliibited at a con- 

 centration of 10 /xgm./ml., and 60-80 percent inhibition occurred at 

 4,000 /Agm./ml. Green pigments accumulating in the presence of anti- 

 biotic were chlorophylls a and 6, and they were found to be present in 

 the same ratio as in leaves treated with water instead of chlorampheni- 

 col. However, the effectiveness of chlorophyll in catalyzing photo- 

 synthesis decreased with increased concentration of chloramphenicol. 

 Chloramphenicol does not affect the photosynthetic ability of leaves 

 greened in its absence. 



Leaves greened in the presence of chloramphenicol did not differ 

 in their content of TPN-dependent glyceraldehyde-3-phosphate de- 

 hydrogenase from water-treated controls. Levels of carboxydismu- 

 tase were somewhat lower in treated leaves. However, Hill reaction 

 activity of a green particle fraction from leaves greened in cliloram- 

 phenicol solution was only a tenth of that of the same fraction from 

 control leaves. 



The rate of chlorophyll synthesis in Black Valentine bean leaves 

 was demonstrated to be another physiological response wliich is sub- 

 ject to the mediation of the red, far-red photomorphogenic receptor. 

 The rate of pigment production by the chlorophyll-synthesizing 

 mechanism in etiolated leaves can be influenced by a short preirradia- 

 tion with red and far-red radiant energy. A treatment consisting of 

 several minutes of red light, followed by an overnight period in dark- 

 ness, results in appreciable stimulation in the subsequent rate of 

 chlorophyll synthesis in continuous wliite light. The stimulation in- 

 duced by a red pretreatment can be nullified by subsequent exposure 

 to far-red, either immediately after the red induction or even after 

 interposing as much as 9 hours of darkness. TNHien red and far-red 

 are administered alternately for several cycles, the quality of the ter- 

 minal treatment controls the rate of chlorophyll synthesis. The effect 

 of the red, far-red system on the chlorophyll-synthesizing mechanism 

 may be due to the synthesis of pigment precursors or to changes in 

 plastid size and/or number. 



The expansion of dark-grown leaves is promoted markedly by ex- 

 posure to red radiant energy. For leaf disks, the induction by red 

 is a logaritlimic function of dose over the range of 0.1 to 100 mj./cm.^ 

 when given in 100 seconds. For reversal, the dose response curve is 

 a linear function of dose, and the maximum effectiveness of the far- 



