B. Kassanis

Evidence that a component other than the virus particle is needed for aphid transmission of potato virus Y

Abstract Aphids ( Myzus persicae Sulz) did not transmit potato virus Y after probing into purified virus preparations, but did if these preparations were first mixed with extracts of infected plants from which all potato virus Y particles had been removed by centrifuging. The same centrifuged extracts also ‘helped’ aphid transmission of potato aucuba mosaic virus.

The transmission of potato aucuba mosaic virus by aphids from plants also infected by potato viruses A or Y

Abstract None of twelve strains of potato aucuba mosaic virus (PAMV) tested was transmitted by the aphid Myzus persicae Sulz. from plants infected with PAMV alone. Strains differed in the ease with which they were transmitted from plants which were also infected with either potato virus A or Y. Some were only occasionally transmitted, and others readily—some more readily from plants infected with Y than with A, and others only from plants infected with Y. Infection with either virus Y or A increased the concentration of PAMV, and more so with Y than with A. The transmissibility of PAMV was not correlated with its concentration in expressed sap found in the individual experiments. The concentration of PAMV differed at different seasons and in summer was too low to be detected serologically in plants also infected with virus A.

Comparison of the early stages of infection by intact and phenol-disrupted tobacco necrosis virus

Abstract Preparations of a tobacco necrosis virus disrupted by phenol were nearly as infective as the parent virus preparation when the two were compared in pH 7, 0.06 M phosphate buffer and about one-fifth as infective when compared in water. No virus particles could be detected in the disrupted preparations by electron microscopy, and the preparations were rapidly inactivated by dilute solutions of pancreatic ribonuclease, harmless to the intact virus. At 20° C the preparations became inactive in 1–4 days. Some of the changes detectable in infected bean leaves occur sooner with inoculum of disrupted virus than with intact virus. The infective centers initiated by disrupted virus start to increase their resistance to inactivation by ultraviolet radiation immediately after inoculation whereas those initiated by intact virus do so only after a lag period of 2–3 hours, and newly formed virus becomes detectable 2–4 hours sooner when the inoculum is disrupted virus. The very first lesions produced by each type of inoculum appear simultaneously, but those produced by disrupted virus reach their final number sooner than those produced by intact virus. The peak rate at which lesions appear is about 4 hours earlier with inoculum of disrupted than with intact virus, and the lesions produced are more uniform in size.

Interaction of virus strain, fungus isolate, and host species in the transmission of tobacco necrosis virus

Abstract Transmission of strains A and D of tobacco necrosis virus (TNV) by 3 different isolates of Olpidium brassicae (called 1, 3, 4) was tested on different host plants. The host plants were seedlings of lettuce, cress, and Mung bean and tissues of tobacco and Parthenocissus tricuspidata growing in agar and liquid medium, respectively. Olpidium 4 did not transmit either strain to any host and Olpidium 3 transmitted both more readily than did Olpidium 1. Strain D was usually transmitted more readily than strain A, but Olpidium 1 transmitted A more readily than D to tobacco callus. Apparent differences in transmission of the two strains are not correlated with the hosts ability to support virus multiplication when inoculated mechanically. Nor can specific transmission by Olpidium isolates be explained in terms of different susceptibilities of the hosts to individual olpidia. For example, Olpidium 4 multiplies profusely in cress to which it does not transmit TNV, whereas Olpidium 3 transmits TNV to cress, in which it does not multiply or form zoosporangia. Although Olpidium 1 transmits strain A to tobacco tissues, it does not to lettuce and cress, even in conditions when it makes more penetrations than does Olpidium 3, which transmits the virus. Virus infection in cress roots inoculated with Olpidium 3 and virus can be inhibited by inoculating the roots later with Olpidium 4. The inhibition can be destroyed by heating the doubly inoculated roots at 50° for 10 seconds, which inactivates the fungus but not the virus. Other olpidia that do not transmit strain D to cress, but do so to other hosts, also inhibited transmission by Olpidium 3. The results suggest that vector specificity may be determined, at least in part, by responses of the host cells, and that whereas some olpidia produce changes in the cells that favour virus infection others produce changes that prevent it.

Unstable variants of tobacco necrosis virus

Abstract From single lesions caused by two strains of tobacco necrosis virus variants were isolated that were unstable in sap and difficult to maintain by inoculation with sap. Extracts of leaves infected with these variants in water-saturated phenol or in 0.5 M borax pH 9.2, were 10–100 times more infective than sap. The results are consistent with the idea that the unstable variants occur in the plant largely as nucleic acid, which is destroyed by leaf ribonuclease when the leaves are ground in conditions that allow the enzyme to act. Although most of the infectivity of these variants resides in unstable particles, there are in most, if not all populations some stable particles, presumably composed of nucleoprotein, which retain their infectivity in sap and survive purification procedures. About 1 in 20 of the lesions formed by purified preparations of the two strains of tobacco necrosis virus yielded the unstable variant only. During repeated transmission in series the unstable variant did not give rise to stable ones. The satellite virus that multiplies only in leaves simultaneously infected with certain strains of tobacco necrosis virus, multiplied in leaves infected with the unstable variant, but less extensively than with the stable variant.

The relationship between barley stripe mosaic and lychnis ringspot viruses.

Abstract Purified preparations of barley stripe mosaic and lychnis ringspot viruses contained similar rod-shaped particles. When shadowcast, the particles had a modal length of about 125 mμ and were 18–19 mμ wide. Negatively stained particles showed a central canal and a regular cross banding at 2.5-mμ intervals. The two viruses are distantly serologically related.

The protein and nucleic acid of beet yellows virus

By analysis on SDS-polyacrylamide gels, the coat protein of beet yellows virus was shown to consist of a single polypeptide of molecular weight about 22,400. The amino acid composition and tryptic peptide map also indicate a molecular size close to 22,000. Viral RNA comprising 6% by weight of the particles is single stranded and has the base composition U, 23%; C, 22%; A, 27%; G, 28%. Its size, estimated by sedimentation and gel electrophoresis, is close to 4.6 × 106. We propose that in the virus particle the single helical RNA strand is embedded at a radius of 3.3 nm in a protein coat comprised of approximately 3400 protein subunits, giving a total particle weight of 80 million daltons.

Some effects of varying temperature on the quality and quantity of tobacco mosaic virus in infected plants.

Abstract From tobacco plants inoculated with isolates of virulent tobacco mosaic virus recently derived from single lesions, avirulent variants were readily obtained when the tobacco plants were maintained at 36° but not when they were maintained at 20°. The avirulent variants reached higher concentrations than the parent strain in plants kept at 36°. Both types reach much the same concentration in plants at 20° and only occasionally can virulent variants be isolated from tobacco plants inoculated with the avirulent ones and kept at 20°. The relative concentrations reached at 20° and 36°, depend not only on the identity of the strain of tobacco mosaic virus used, but also on the species of plant inoculated. Some strains seem unable to initiate infection in Niootiana glutinosa at 36° although they persist at this temperature in cells that are infected at 20°. Type tobacco mosaic virus is unstable in tobacco plants at 36° and the virus content of sap slowly decreases when plants are kept at this temperature.

Purification and some properties of beet yellow virus

Abstract Beet yellows virus was purified by a method, based on ultracentrifuging at 35,000 g, that preserved the normal length of the virus particle and eliminated a uv-absorbing contaminant retained by previously described methods. The purified particles had a modal length in shadowed preparations of 1250 nm and sedimented in the analytical centrifuge usually as one component at 130 S. Purified preparations had an A 260 A 280 ratio of 1.44 and an extinction coefficient at 260 nm of 2.9. In Cs2SO4 isopycnic banding, the virus had a density of 1.285 g/cm3, while in CsCl two bands were produced at 1.307 and 1.312 g/cm3.

Thermal inactivation of tobacco necrosis virus

Abstract The thermal inactivation point of different strains of tobacco necrosis virus (TNV) in infective sap ranged between 85° for strain B and 95° for strains D and E. Determination of inactivation points and results of kinetic experiments place the six strains in the same order of susceptibility to heat. TNV did not become inactivated exponentially at the same rate at all survival levels. The virus apparently was inactivated at two different rates, as though it consisted of two components. At high temperatures the more resistant component was a small fraction of the total, but increased with decreasing temperature and at about 40° was the only one detectable. The inactivation rates of the two components differed greatly and increased with increases in temperature. The ratio of the two components and their inactivation rates at different temperatures differed with different strains. The changing ratio of the two components, and some other properties of the strains, show that the virus preparations were initially homogeneous and that the two components were produced by heating. Nucleic acid extracted from strains A and E with phenol became inactivated similarly at 50° to intact virus, indicating that changes in the nucleic acid are responsible for thermal inactivation of the virus. Inactivation to 1% survival in water or acid buffers did not alter the antigenicity, sedimentation coefficient, or the UV absorption spectrum of the virus. Also, there was no evidence that nucleic acid was released under these conditions.