FAMILY MARMORACEAE 



1165 



Through dodder, Cuscuta campestris 

 Yuncker (CONVOLVULACEAE), with- 

 out infecting this plant vector. Not 

 through pollen from diseased plants. 

 Not through seeds from diseased tobacco ; 

 seed transmission has been reported in 

 the case of recently ripened seeds from 

 diseased tomato. 



Serological relationships : Precipitin 

 test gives cross reactions between all 

 known strains, except those characterized 

 by failure to spread systemicallj' in to- 

 bacco. No cross reactions with other 

 viruses except weakly with cucurbit - 

 mosaic virus {M armor astrictum). Type 

 and other strains of tobacco-mosaic virus 

 give cross reactions in complement -fixa- 

 tion and neutralization tests. 



Immunological relationships : Plant 

 protection tests, particularly in Nicotiana 

 sylvestris Spegaz. and Comes, have dem- 

 onstrated that tissues invaded by any 

 strain of this virus are immune to subse- 

 quent infection by the tomato aucuba- 

 mosaic strain of tobacco-mosaic virus, 

 indicating a group relationship not shared 

 by other viruses, such as cucumber- 

 mosaic virus or tobacco-ringspot virus. 



Thermal inactivation : At 88 to 93° C 

 in 10 minutes ;at 86 to 92° C in 30 minutes. 



Filterability : Tobacco -mosaic virus 

 was the first virus shown to be filterable, 

 by Iwanowski in 1892; its filterability was 

 confirmed and interpreted by Beijerinck 

 in 1898. 



Other properties: The ultimate parti- 

 cles of tobacco-mosaic virus have been 

 shown to be rod-shaped and isotropic, 

 sometimes associated in pairs, end to end. 

 Under proper conditions, thread-like 

 paracrystals are formed. Specific gravity 

 has been determined as about 1.37, re- 

 fractive index as about 1.6. Lsoelectric 

 point between pH 3.2 and 3.5. Suspen- 

 sions in media of lower refractive indices 

 show anisotropy of flow. Sedimentation 

 constants, at 20° C, 187 X IQ-i^ cm per 

 sec. per dyne at infinite dilution for un- 

 aggregated virus and 216 X 10"^^ cm per 

 sec. per dyne for associated particles. 

 The computed average length of the virus 



unit is about 272 millimicrons; diameter, 

 13.8 millimicrons. Electron micrographs 

 show that characteristic particles are rod- 

 like, between 10 and 20 millimicrons in 

 width, variable in length, but in some 

 preparations averaging 270 millimicrons 

 in length for single units, 405 to 540 milli- 

 microns in length for associated pairs; 

 X-ray measurements in air-dr}^ gel show- 

 width 15.20 ± 0.05 millimicrons. Solu- 

 tions stronger than about 1 .3 per cent sep- 

 arate into layers, the lower spontaneously 

 doubly refracting and more concentrated 

 than the upper. At concentrations of 

 electrolytes somewhat less than are re- 

 quired to precipitate the virus as fibres 

 or needle-shaped paracrystals, the solu- 

 tions form clear gels that become fluid 

 on shaking or diluting (at pH 7 and 30° 

 C). The virus is destroyed by high-fre- 

 quenc}- sound radiation, by pressures be- 

 tween 6000 and 8000 kilograms per square 

 centimeter, and by hydrogen-ion con- 

 centrations above pH 11 or below pH 1. 

 It is relatively stable between pH 2 

 and pH 8. It is rapidly broken down in 

 6 M urea solutions, in the presence of 

 salts, to low-molecular-weight compo- 

 nents devoidof activity. Analysisof puri- 

 fied virus : carbon 47.7 per cent, hydrogen 

 7.35 per cent, nitrogen 15.9 per cent, sul- 

 fur 0.24 per cent, phosphorus 0.60 per 

 cent, lipoid 0.0 per cent, carbohydrate 1.6 

 to 2.0 per cent . A revised estimate of the 

 sulfur content is 0.20 per cent, probably 

 all in cysteine ; no methionine has been 

 detected in the typical variety of this 

 virus. The percentages of the following 

 substances in the virus are: tyrosine 3.9, 

 tryptophane 4.5, proline 4.6, arginine 9.0, 

 phenylalanine 6.0, serine 6.4, threonine 

 5.3, cysteine 0.68, alanine 2.4, aspartic acid 

 2.6, glutamic acid 5.3, leucine 6.1, valine 

 3.9, nucleic acid 5.8, and amide nitro- 

 gen 1.9, collectively accounting for 

 about 68 per cent of the total weight. 

 Virus formation ceases in infected host 

 tissues immersed in 0.0002 molar sodium 

 cyanide solution, beginning again after 

 removal of cvanide. 



