I.R. Schneider

Characteristics of a satellite-like virus of tobacco ringspot virus

Abstract A heterogeneous population of viral particles (SL-TRSV), some of which sediments almost as fast (122 S) as the bottom component (126 S) of tobacco ringspot virus (TRSV), was discovered as an unexpected part of a mixed infection with TRSV. Although SL-TRSV appears to be dependent upon TRSV for its own replication, SL-TRSV commonly becomes the major portion of the virus population. SL-TRSV is not as homogeneous as either middle or bottom component of TRSV, but rather sediments with a range of rates between middle and bottom component of TRSV (91–126 S); yet the nucleic acid extracted from SL-TRSV is homogeneous and sediments at only 7.3 S in contrast to the nucleic acids extracted from TRSV, which sediment at 24 S and 32 S. The 7.3 S nucleic acid of SL-TRSV appears to be single-stranded and RNase sensitive. Thus, according to Gierers formula, a molecular weight of only 86,000 daltons is indicated for the nucleic acid of SL-TRSV. Both SL-TRSV and TRSV are indistinguishable in size and shape and in serological tests. SL-TRSV was not detected in plants inoculated either with the 7.3 S nucleic acid alone or with TRSV (strain ST) alone, but was detected in plants inoculated with a mixture of the 7.3 S nucleic acid and TRSV. Lesions in blackeye cowpeas resulting from inoculation with the mixture were distinct from those induced by TRSV alone. The 7.3 S nucleic acid alone induced no visible lesions at 5 μg/ml; but the 7.3 S nucleic acid at 0.004 μg/ml, in combination with TRSV, induced some tiny lesions typical of SL-TRSV. These results suggest that SL-TRSV cannot replicate in the absence of TRSV; and that each capsid of SL-TRSV, which may be identical to a capsid of TRSV, can contain from 14 to 26 strands of nucleic acid of uniform length. The nucleic acid strands within the capsid, or extracted from the capsid, are biologically active when used in inoculum together with TRSV.

Introduction, translocation, and distribution of viruses in plants.

Publisher Summary The introduction of viruses into different tissues and portions of the plant is considered especially in relation to their subsequent translocation and distribution. The infection by viruses and their multiplication are treated in relation to translocations and distribution, but are not discussed in detail. Movement from cell to cell may be via different pathways, and advances in knowledge about translocation of viruses along these pathways, together with some remaining questions, are indicated. Movement of a virus refers to the movement of unknown form(s) of virus particles, which have one cell and initiate infection in another cell. The evidence for possible translocating forms of a virus is discussed. The possible mechanisms of transport of viruses are a part of the general problem concerning the transport of solutes. The distribution of viruses within plants may be extensive or restricted, and data concerning different distribution patterns are discussed in the chapter. The primary infections initiated by viruses may originate in different regions and in different tissues of the plant. The translocation and distribution of a virus will be affected by the number and location of these primary infection sites. The translocation of viruses within plants cannot be placed on a quantitative basis or studied directly and separately from other interrelated phases of virus infection and multiplication. The subsequent distribution of virus in a quantitative sense depends on a complex of interactions between virus and the different cells of the host, rather than solely on the number of virus particles and their rate of translocation. Knowledge concerning the distribution of virus within different tissues has been forwarded by careful studies of the development of primary characteristic symptoms. Translocation pathways have also been implicated in such investigations. Characteristic crystals, some shown to be almost wholly composed of virus, have aided in obtaining distribution profiles of virus.

Multidense satellite of tobacco ringspot virus: A regular series of components of different densities

Abstract Satellite of tobacco ringspot virus (S-TRSV) is composed of at least 11 and possibly as many as 14 components, ranging in density from ϱ = 1.408 through ϱ = 1.529. Each component differs in buoyant density from its nearest neighbor by approximately †ϱ = 0.009. The buoyant density of middle component of tobacco ringspot virus is approximately ϱ = 1.423, about †ϱ = 0.015 greater than that of the S-TRSV component with the lowest buoyant density. Bottom component of tobacco ringspot virus is composed of two populations, one population with an average ϱ = 1.507 and the other with an average ϱ = 1.518. The buoyant densities found in a S-TRSV population are not artifacts caused by CsCl, but are characteristic of the population before the particles are exposed to CsCl, and correlate with the position of the particles sedimenting in a sucrose gradient. Since some TRSV particles are always in S-TRSV preparations, the three components with densities approximating those of bottom and middle, may not be S-TRSV. Thus S-TRSV is composed of at least 11, but possibly 14 components. A high proportion of satellite to TRSV in inoculum resulted in a high proportion of S-TRSV in the infected plants. Plants inoculated with TRSV and “low-density” S-TRSV yielded both “high” - and “low-density” S-TRSV as well as TRSV. No significant difference was detected in the base ratio of the nucleic acids within TRSV (strain WS)—middle or bottom components—and the base ratio of the nucleic acid strands within S-TRSV that had been activated by TRSV (strain WS). The data fit with the following view. All S-TRSV particles contain numerous nucleic acid strands of uniform size, each strand approximating 86,000 daltons. Each S-TRSV particle of the lowest buoyant density has approximately 12 nucleic acid strands; each S-TRSV particle of higher density has one more nucleic acid strand than its nearest neighbor of lower density. Most members of this continuous series are consistently found in purified preparations of S-TRSV. Particles with the highest density contain approximately 25 nucleic acid strands per particle.

Phycovirus SM-1: a virus infecting unicellular blue-green algae.

Abstract We describe the purification of a new blue-green algal virus SM-1, which infects only unicellular forms. The new virus appears to be a polyhedron with no obvious tail and with an average diameter of about 88 mμ. Several characteristics indicate that this virus is distinct from the blue-green algal virus LPP-1. Two infectious nucleoproteins were usually found in sucrose-density gradients. The faster component aggregated readily, and its instability appeared to account for the variations in the relative proportion of the two components. The sedimentation coefficient of the slower sedimenting component ( s 20w ) was 1.021–1.029. The nucleic acid is a double-stranded DNA. The new SM-1 virus, unlike the algal virus, LPP-1, does not appear to resemble basic morphological phage types.

Rapid entry of infectious particles of southern bean mosaic virus into living cells following transport of the particles in the water stream

Abstract Infectious particles of southern bean mosaic virus moved upward in the water stream of Pinto bean stems, entered undamaged living cells, and multiplied. In some plants the time required to enter living cells several feet from the site of virus intoduction must have been 1 day or less. Introduction of virus directly into steamed regions of Pinto stems resulted in occurrence of virus infections far above the point of virus introduction. Local infections at site of virus introduction were therefore not prerequisite to the occurrence of remote infections. Introduction of the virus into an internode well above the hypocotyl also resulted in the frequent occurrence of necrosis in foliage above the inoculated area, but rarely in that below. Rapid upward transport of infectious virus particles in the water stream with a pathway for natural entry of these particles into living cells is indicated by the results obtained.

The correlation between the proportions of virus-related products and the infectious component during the synthesis of tobacco ringspot virus

Abstract A time study has suggested that at least one, of two noninfectious components found in tissues of plants infected with tobacco ringspot virus (TRSV), is synthesized concurrently with virus multiplication. Three components found in infected (but not in uninfected) tissues are referred to as top, middle, and bottom components, according to their relative positions after density gradient centrifugation. In purified preparations of a WS-strain from leaves collected 2 1 2 –3 days after inoculation, the amount of middle as compared to the amounts of middle plus bottom components combined varied between 39 and 58% (mean: 46%), based upon ultraviolet absorption at 260 mμ. On the other hand, the amount of middle component in preparations from leaves collected 6 or 7 days after inoculation varied between 17 and 38% of the mixture (mean: 25%). Although the middle component was a smaller proportion of the mixture at 6 or 7 days than at 2 1 2 or 3 days, it had actually increased an average of threefold, while the bottom component (the infectious particle) had increased an average of eightfold. Thus, between 0 and 3 days the middle component increased more rapidly in relation to the bottom component than between 3 and 7 days, when the middle component increased more slowly than the bottom component. In older infections (14 and 21 days after inoculation), the middle component either was a smaller portion of the mixture, or remained approximately the same portion. The direction of the shift in the proportion of noninfectious and infectious particles with time after inoculation was basically the same for a strain of TRSV (ST) that contained, upon purification, a much smaller proportion of middle component than TRSV (WS). Both middle and bottom components of the ST strain increased at a much slower rate than the corresponding middle and bottom components of the WS strain. Our data are consistent with the view that the noninfectious middle component is a product intimately connected with the synthesis of tobacco ringspot virus. The middle component does not appear to be the result of degradation from infectious particles either in vivo or during the course of purification. However, the middle component is not necessarily a precursor of the bottom component. It appears more likely that the middle component is synthesized concurrently with the infectious bottom component and by means of the same pool of protein and nucleic acid subunits.

Upward and downward transport of infectious particles of southern bean mosaic virus through steamed portions of bean stems

Abstract Infectious particles of southern bean mosaic virus (SBMV) moved from living cells into the water stream of the tracheary system in Pinto bean stems, then upward or downward. Later, these particles established new infections in distant cells. Transport in the tracheary system apparently occurred upward more frequently and rapidly than downward and in most instances involved greater distances. Evidence is presented that virus detected beyond steamed regions was present as a result of transport of virus particles through the steam-treated regions, and not due either to chance introduction of virus from external sources or to multiplication of virus in cells of the steam-treated region. Discussion of the results presented here and elsewhere summarizes the basis for the authors belief that it is possible for particles of SBMV to move long distances in tracheary elements as well as in sieve tubes of a local-lesion host (Pinto bean). With superficial mechanical inoculations of the same variety, infectious particles do not move long distances, but when the virus is introduced deeply into the host, particles may enter one or both of the rapid long-distance transport systems, i.e., the xylem or phloem.

Potato spindle tuber viroid. XI. A comparison of the ultraviolet light sensitivities of PSTV, tobacco ringspot virus, and its satellite

Abstract Exposure of purified potato spindle tuber viroid (PSTV), of tobacco ringspot virus (TRSV), and of its satellite (SAT) to ultraviolet light of 254 nm, followed by determination of residual infectivity levels, indicated that the inactivation doses for PSTV and SAT are 70–90 times larger than the dose for TRSV. The high resistance of PSTV and SAT to uv irradiation may be due to the small sizes of PSTV and SAT-RNA.

Electron microscopy of double-stranded nucleic acids found in tissue infected with the satellite of tobacco ringspot virus

Electron microscopic studies of the ds RNAs purified from plants infected with the satellite (S) of tobacco ringspot virus (TobRSV) revealed that approximately 91% of the population is linear, varying in length between 40 and 3000 nm. Six percent of the population appeared as relaxed circles, and the balance appeared as racket-like structures. Electrophoretic analysis of these preparations detected at least 12 components higher in molecular weight than the expected 230,000-dalton RF. Denaturation of the same sample released ss RNA that coelectrophoresed with STobRSV RNA from virions. The linear ds molecules, although extremely variable in length, have some preferential distribution around 130 nm, not around 68 nm, the length of ss STobRSV RNA; the circles also varied, but their lengths fell into four distinct peaks: the shortest was 130 nm, and the increment of each longer circle was also about 130 nm. The circular portion of the racket-like structure was a uniform 130 nm, with a varied linear portion. However, the most frequent linear dimension was also 130 nm. Denatured ds RNA varied in length, and most molecules fell in between 50 and 185 nm. Relaxed circles and racket-like structures were also present, but much less frequently than in the undenatured preparation. T1 RNase degradation of ds StobRSV RNA made the linear population more uniform in length (between 60 and 130 nm), most preferentially around 130 nm, and decreased the number of circles and racket-like molecules.

Double-stranded nucleic acids found in tissue infected with the satellite of tobacco ringspot virus.

Abstract We have purified a multicomponent population of RNAs from tissue infected with the satellite of tobacco ringspot virus (S-TRSV) that is not present in tobacco ringspot virus-(TRSV-)infected tissue or in uninfected tissue. Many of the properties are characteristic of dsRNA, or the so-called replicative form of small RNA viruses; i.e., a sharp melting profile at relatively high temperature and high hyperchromicity and buoyant density in cesium sulfate; the RNAs are infective only after denaturation and quick quenching, followed by addition of TRSV. The infectivity is not destroyed prior to denaturation either by pancreatic RNase (in high ionic strength buffer) or by incubation with formaldehyde. Other properties are not typical of dsRNAs: At least 83% of the RNAs elute from CF-11 cellulose columns in buffer (0.1 M NaCl, 0.05 M Tris, 0.001 M EDTA, pH 6.9)/ethanol mixtures that typically elute ssRNAs but not dsRNAs. The RNA is composed of many components, some of which are up to 20 times the mass one would expect from the known mass of the corresponding RNAs found in S-TRSV virions. Pancreatic RNase, at relatively high concentrations, converts these higher-molecular-weight dsRNAs into dsRNAs of lower molecular weight. These lower-molecular-weight double-stranded components retain a high level of infectivity after denaturation (with added TRSV).