120 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



Strengthened as more data accumulate. It is hoped that a daily de- 

 termination from our holographs of the quantity of ozone in the upper 

 atmosphere may become a regular part of our records at the Table 

 Mountain station. 



DrVTSION OF RADIATION AND ORGANISMS 



(Report prepared by R. B. Witetrow) 



During the past 2 years the division of radiation and organisms has 

 been setting up specialized equipment and facilities for an investiga- 

 tion of the plant photochemical reactions involving photomorpho- 

 genesis, which is a light reaction controlling the growth and develop- 

 ment of higher plants, and photoperiodism which is another light 

 reaction controlling the flowering of many higher plants. Wave- 

 lengths in the red end of the spectrum from about 600 to 700 m/* are 

 the most effective in producing these responses. 



The first experimentation has involved photomorphogenesis as it 

 pertains to the effect of red light on leaf expansion and pigment forma- 

 tion in seedlings of bean and corn. In the dark, a young bean seedling 

 develops with a sharp bend just below the bud, called a plumular hook, 

 and the leaves fail to develop beyond a very immature stage. With 

 very low intensities of red light, leaf expansion occurs quite rapidly, 

 nodes develop from the bud, and the plant form approaches normal. 

 Heretofore, with such developmental reactions there has always been 

 associated other photochemical reactions as chlorophyll synthesis 

 and photosynthesis. 



Since the elucidation of the biochemistry of photomorphogenesis 

 is greatly complicated by the simultaneous occurrence of other light- 

 controlled reactions, an attempt has been made to induce photomor- 

 phogenesis independently of other light processes. Special dyed gel- 

 atin light filters have been prepared which have a sharp cut-off at 

 about 730 m/x, so that they transmit only wavelengths longer than the 

 cut-off, but strongly absorb the shorter wavelengths. In bean it has 

 been found possible to cause almost complete development of leaves 

 and the first few internodes without any measurable synthesis of 

 chlorophyll ; thus photomorphogenesis has been excited with only the 

 most minute traces of chlorophyll synthesis, no photosynthesis, and no 

 phototropic reaction. From this it is evident that the photomorpho- 

 genic reaction has an action spectrum that goes a little farther into 

 the infrared than that of the other photochemical reactions. 



By using the 436 m/* line from a mercury arc isolated with a blue 

 filter, it has been possible to produce bean plants in which the leaf 

 development occurred to a very small degree, but yet considerable 

 chlorophyll synthesis took place. The blue-treated plants had 

 roughly 10,000 times as much chlorophyll as the 730-m/A-treated 



