Figure 3.— An assay of phytochrome in the dual- 

 monochromator spectrophotometer starts with 

 centering a sample, such as a bean seedling, 

 so that the 12-inch sphere and projecting 

 phototube can be lowered over it. The ob- 

 long base houses the lamp for measuring 

 pigment changes, lenses, mirrors, and other 

 optical parts of the instrument, as well as 

 the electrical measuring equipment. The op- 

 erator applies irradiation of two pre-selected 

 light waves alternately to the sample, end 

 the meter readings on the dial show the 

 change in phytochrome's form. The amount 

 of change indicates the concentration of the 

 pigment. Wove lengths used have generally 

 been 6600 A. for red and 7350 A. for far red, 

 because these are about the peaks of effec- 

 tiveness for controlling the plant photoreac- 

 tions. 



These separation processes have yielded an extract in a test tube that is 

 phytochrome much more concentrated than in the plant, its identity proved 

 by its reactions in the pignaent-detecting instrument. The greenish extract 

 is only partially purified, that is, it contains some other plant proteins. 



Total isolation of phytochronae is being tried for. This may be a 

 time-consuming, arduous task. Yet isolation is an essential step if 

 research scientists are to identify the elements and structure of the 

 chemical molecule that is so vital a part of plant organism. And only 

 when this information is available can they make solid progress in 

 learning the way in which plants get or make their phytochrome and the 

 way in which phytochronne's elennents serve in enzyme reactions, such 

 as the fat utilization that governs germination in some seeds and the 

 coloration processes in vegetables and fruits. 



Phytochronne in test tubes reacts as a soluble protein. Knowing its 

 nature scientists can project its manner of serving plants a step forward. 

 Apparently, the colored protein's molecular shift under red light influence 

 enables the protein to function as an active enzyme; and this enzyme is 

 the triggering agent that actually launches a growth change. Proteins 



13 



