VIRUSES 



iflGDRE 2 - PARACRYSTAL5 OP TOBACCO MOSAIC VIRUS 

 PROTEIN. 1675. ('• M. Stanley, Ergeb. Physiol. 29, 

 29* (1937) ). 



It must be emphasized that this material is in no sense an ordinary substance, 

 for if these crystals are dissolved In water and then diluted a million fold, 

 the solution will still be hi^ly Infectious and will institute disease in 

 tobacco plants. 



ThlB picture gires a clue as to how purified tobacco mosaic virus can be 

 obtained. Young tobacco plants are infected and allowed to grow for 3 ^o 8 

 weeks, and then they are harvested, frozen and ground. The Juice is expressed 

 the virus is precipitated out by the addition of ammonium sulfate. After re- 

 preclpltatlon a few times, the crystalline form is obtained. This is approxi- 

 mately the way Stsmley first obtained purified tobacco mosaic virus, but the 

 method is a bit too severe. Today there is a much better means of obtaining 

 the material. Because of its high molecular weight, a value in the millions, 

 it is possible to isolate this material from plant juice by simply centri- 

 fuging at high speed. 



The yield of tobacco mosaic virus from diseased tobacco plants Is amaz- 

 ingly high, about three parts per thousand of the plant niaterlal. Some of the 

 virus is stored in the plant tissues in the form of both amorphous and crystal- 

 line inclusion bodies. A photomicrograph of hexagonal plate-like inclusion 

 bodies, composed largely of stored virus, inside one of the hair cells of a 

 mosaic diseased plant is reproduced as Pigure 3* 



