Further studies on the ultrafiltration of plant viruses

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Abstract
An account is given of ultrafiltration studies with 9 plant viruses. It is shown that 3 of these viruses filter in a consistent manner and appear to have approximately spherical particles. These three areLycopersicum virus4 (tomato bushy stunt virus),Nicotiana virus11 (tobacco necrosis virus) andNicotiana virus12 (tobacco ringspot virus). The filtration end-point of 40 mμ is the same in each case and from this a particle diameter of 13–20 mμ is calculated. There is a peculiarity, however, in the filtration curve of tobacco necrosis virus which shows itself in a “bench” or “shelf” and which suggests either a polydisperse system or some degree of dissymmetry of particle shape.Great difficulty was experienced in filteringNicotiana virus1 (tobacco mosaic virus) and its strains. A value of 13–20 mμ was obtained for the particle diameter of the type virus and this agrees well with measurements obtained by other methods. The filtration results, however, suggest that the infective units are not of the same length and that this variability may be considerable. Similar difficulty was experienced in filteringSolanum virus1 (potato virus X), another rod-shaped virus; the end-point was found to be 100 mμ, from which a particle diameter of 33–50 mμ is calculated. It was not possible to obtain a definite filtration end-point forCucumis virus1 (cucumber mosaic virus), probably because of the low initial concentration of virus in the extracted sap.