Particle purification and properties of cassava Ivorian bacilliform virus

A virus found in cassava from the north-west of the Ivory Coast was transmitted by inoculation with sap extracts to herbaceous species in six plant families. Chenopodium quinoa was used as a propagation host and C. murale was used for local lesion assays. The virus particles are bacilliform, c. 18 nm in diameter, with predominant lengths of 42,49 and 76 nm and a structure apparently similar to that found in alfalfa mosaic virus. Purified preparations of virus particles had A₂₆₀/A₂₈₀ of 1.7 ±0.05, contained one protein of M_rc. 22 000, and yielded three species of RNA with M_r (× 10^-6) of c. 0.7, 0.8 and 1.2. Although the virus particles were poorly immunogenic, an antiserum was produced and the virus was detected by enzyme-linked immunosorbent assay (DAS-ELISA) in leaf extracts at concentrations down to c. 6 ng/ml. Four other field isolates were also detected, including a strain which caused only mild systemic symptoms in C. quinoa instead of necrosis. The naturally infected cassava source plants were also infected with African cassava mosaic virus (ACMV) but when the new virus was cultured in Nicotiana benthamiana, either separately or together with ACMV, its concentration was the same. The new virus did not react with antisera to several plant viruses with small bacilliform or quasi-bacilliform particles, and alfalfa mosaic virus reacted only weakly and inconsistently with antiserum to the cassava virus. The new virus, for which the name cassava Ivorian bacilliform virus is proposed, is tentatively classified as the second member of the alfalfa mosaic virus group.     

Some Characteristics of Potyvirus Isolates from Vanilla tahitensis in French Polynesia and the Cook Islands

Further characterization of vanilla mosaic potyvirus (VaMV) confirmed that it is quite distinct from vanilla necrosis potyvirus (VNV). In immuno-blot ELISA, a polyclonal antiserum to vanilla mosaic virus from Vanilla tahitensis in French Polynesia did not react with vanilla necrosis potyvirus infected V. fragrans from Tonga. However, samples of V. tahitensis with leaf distortion and mosaic from the Cook Islands reacted strongly with the VaMV antiserum. Host range studies involving 20 plant species failed to find a host for VaMV outside the genus Vanilla, confirming that VaMV has a much more restricted host range than VNV. The mean particle length of V_aMV from purified preparations was 763 nm (Std. Dev. 48) and SDS-polyacrylamide electrophoresis indicates a single coat polypeptide of M_r 34 × lO³.     

Elderberry latent virus: its relationship to Pelargonium ringspot virus and its identification as a distinct member of the genus Carmovirus, family Tombusviridae

The properties of Elderberry latent virus (ELV) and Pelargonium ringspot virus (PelRSV) were compared. The viruses were largely indistinguishable in herbaceous host range and symptomatology, particle morphology, sedimentation coefficient and RNA profiles and size. They were also very closely related serologically with SDI differences in agarose gel double‐diffusion tests of 1 to 3. Purified virus particle preparations of each virus contained isometric particles c. 30 nm in diameter that sedimented as a major component with an s^O_20W of 112–115S. Purified virus particle preparations contained a major and a minor ssRNA species that in polyacrylamide gel electrophoresis (PAGE) had estimated sizes of c. 3.8 kb and c. 1.6 kb respectively. Plants of Chenopodium quinoa infected with ELV or PelRSV each contained three dsRNA species of c. 3.8, 2.6 and 1.8 kbp, although the smallest of these species was not evident in all preparations. Protein from purified virus particle preparations contained a major polypeptide that, in SDS‐PAGE, had an estimated M^r of 40 000 (40K). However, after storage of purified virus particles for 7–10 days, protein preparations from PelRSV particles also contained an additional major polypeptide of estimated M^r of 37 000 that is probably derived by degradation of the 40K protein; this additional component was not observed in freshly prepared preparations of ELV. Neither virus was found to be related serologically to 16 other viruses with isometric particles and similar properties. These data, together with the recent finding by other researchers that the smallest RNA species is a sub‐genomic RNA, suggests that both viruses are members of the genus Carmovirus, and that PelRSV is a minor variant of ELV. However, the taxonomic status of these two viruses is discussed in relation to recent brief reports comparing the nucleotide and amino acid sequences of these two viruses.     

Transmission and differentiation of six viruses infecting hogweed (Heracleum sphondylium) in Scotland

Six viruses, code-named HV1-HV6, were transmitted manually and/or by aphids (Cavariella spp. from symptomless wild plants of hogweed (Heracleum sphondylium) in Scotland. HV1 was identified as parsnip yellow fleck virus (PYFV); anthriscus yellows virus, on which it depends for transmission by aphids, was presumably also present in the hogweed plants. HV2 was transmitted manually and by aphids and had very flexuous filamentous particles c. 700–750 nm long; it has affinities with the closteroviruses, and the name heracleum latent virus is proposed. HV3, HV4 and HV5 were transmitted manually, HV3 and HV5 also by aphids, but their particle morphology is unknown. HV6 was transmitted only by aphids and has very flexuous particles up to 1400 nm long; it is presumably a closterovirus distinct from HV2. All the viruses infected cultivated umbelliferous species experimentally but only PYFV is known to infect umbelliferous crops.     

Properties of cocksfoot streak and cocksfoot cryptic, two viruses infecting cocksfoot (Dactylis glomerata) in Scotland

A Scottish isolate of cocksfoot streak virus (CSV-S) was found to have flexuous filamentous particles which, in sap of infected cocksfoot plants, had a modal length of 712 nm. It was transmitted from infected to healthy cocksfoot plants in a non-persistent manner by Myzus persicae and by mechanical inoculation of infective sap extracts containing an anti-oxidant. Apart from cocksfoot, mechanical inoculation of infective sap succeeded in infecting only four of 22 plant species tested. The infectivity of sap extracts containing 0.2% thioglycerol was lost after heating for 10 min at 55^oC but not 50^oC, storage at room temperature for 48 but not 24 hours, and after diluting 10^-2to 10^-3. Highly purified preparations of CSV-S particles sedimented as a single component with a sedimentation coefficient of 139S and had a buoyant density in rubidium bromide of 1.31 g/cm³. Virus particles were composed of one protein and one ssRNA species with estimated M_r of 31 000 and 3.2 times 10⁶respectively. In ELISA, an antiserum prepared to CSV-S detected the virus in all aerial parts of infected cocksfoot plants and, when present in the ratio of 1 infected leaf: 1000 healthy leaves. Both CSV-S-infected and -uninfected cocksfoot also contained a previously undescribed virus with isometric particles c. 30 nm in diameter. This virus, named cocksfoot cryptic virus (CCV), was seed-borne in two cvs of cocksfoot tested and its particles contained two dsRNA species of estimated M_r of 1.14 times 10⁶and 1.27 times 10⁶. Despite the fact that particles of CSV-S were largely free from CCV particles following exclusion chromatography on agarose beads prior to immunisation, immunoelectron microscopy (IEM) showed that the antiserum prepared to CSV-S also contained some antibodies to CCV. Evidence from IEM suggested a possible distant serological relationship of CCV to ryegrass and beet (BCV 1 or BCV 2, or both) cryptoviruses, all members of sub-group A of crypto viruses.     

Isolation and characterization of ferritin from the hepatopancreas of the musselMytilus edulis

Summary The main iron-binding protein in the hepatopancreas of the musselMytilus edulis, which had been previously iron-loaded by exposure to carbonyl iron (spheres of elemental iron less than 5 m diameter), has been isolated to electrophoretic purity and identified as ferritin. This ferritin hasM _r, of 480000, pI of 4.7–5.0 and is composed of two subunits,M _r 18500 andM _r 24600. Under the electron microscope, it appears as electron-dense iron cores of average diameter 5 nm surrounded by a polypeptide shell to a final average overall diameter of 11 nm. The purified protein contains, on average, 200 iron atoms/molecule protein. On immunodiffusion,M. edulis hepatopancreas ferritin gives a partial cross-reaction with antiserum to horse spleen ferritin and lamprey (Geotria australis) liver ferritin but does not react with antiserum to chiton (Acanthopleura hirtosa) haemolymph ferritin.     

Purification and properties of sweet potato mild mottle, a white-fly borne virus from sweet potato(Ipomoea batatas) in East Africa

A virus obtained from sweet potatoes in Kenya, Uganda and Tanzania was transmitted by inoculation of sap and by whiteflies (Bemisia tabaci). It infected forty-five of 119 plant species in fourteen of thirty-six plant families. It was propagated in Nicotiana glutinosa and N. tabacum, in which diagnostic symptoms of vein clearing, leaf curling and distortion developed. Cheno-podium quinoa was a good local lesion host. Different seedling lines of sweet potato differed greatly in their susceptibility to infection and in symptoms produced; some developed leaf mottling and were stunted, some were symptomless, and some appeared immune. The virus was transmitted by dodder (Cuscuta campestris) but not by aphids, or through seed of Ipomoea nil or N. clevelandii. Sweet potato sap contained strong inhibitors of infection, and a low concentration of virus. Virus-free cuttings of sweet potato were obtained by thermotherapy (4–5 wk at 35 °C), or by meristem-tip culture. The virus remained infective in sap of N. tabacum after dilution to 10-³, or after 10 min at 55 °C (but not 60 °C), 3 but not 7 days at 18 °C, or 42 but not 49 days at 2 °C. Infectivity was abolished by sonication or u.v. irradiation, by 2% formaldehyde or 2% tri-sodium orthophosphate, and was greatly decreased by 20 % CHC1₃ or 20 % ether. Purified virus preparations were obtained from N. tabacum by clarifying phosphate buffer extracts with n-butanol, virus precipitation with polyethylene glycol, and differential centrifugation. The virus sedimented as one band in density gradients, and produced a single sedimenting boundary in analytical centrifugation (s°20, w = 1555)- It contained one polypeptide species of mol wt 37700, and preliminary digestion experiments suggested a single-stranded RNA. Antisera prepared against the virus reacted specifically in precipitin tube tests with titres of 1/16384, but no serological relationships could be found between the virus and fourteen viruses of the potato virus Y group. Electron micrographs showed straight, filamentous particles c. 950 nm long when mounted in MgCl_a, but 800–900 nra long in EDTA. The present cryptogram is: (R/i):*/*:E/E:S/Al. This virus is probably the same as Sheffield's virus B.     

Development of transgenic sweet potato with multiple virus resistance in South Africa (SA)

Multiple infections of Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato virus G (SPVG) and Sweet potato mild mottle virus (SPMMV) cause a devastating synergistic disease complex of sweet potato (Ipomoea batatas Lam.) in KwaZulu-Natal, South Africa. In order to address the problem of multiple virus infections and synergism, this study aimed to develop transgenic sweet potato (cv. Blesbok) plants with broad virus resistance. Coat protein gene segments of SPFMV, SPCSV, SPVG and SPMMV were used to induce gene silencing in transgenic sweet potato. Transformation of apical tips of sweet potato cv. Blesbok was achieved by using Agrobacterium tumefaciens strain LBA4404 harboring the expression cassette. Polymerase chain reaction and Southern blot analyses showed integration of the transgenes occurred in six of the 24 putative transgenic plants and that all plants seemed to correspond to the same transformation event. The six transgenic plants were challenged by graft inoculation with SPFMV, SPCSV, SPVG and SPMMV-infected Ipomoea setosa Ker. Although virus presence was detected using nitrocellulose enzyme-linked immunosorbent assay, all transgenic plants displayed delayed and milder symptoms of chlorosis and mottling of lower leaves when compared to the untransformed control plants. These results warrant further investigation on resistance to virus infection under field conditions.     

Identification of an Arylphorin-type Storage Protein in the Sweet Potato Hornworm, Agrius convolvuli

A major hemolymph protein (M_r 480,000) in the larvae of the sweet potato hornworm, Agrius convolvuli, was purified and characterized. This protein was isolated with a high yield from the hemolymph of day 3 fifth final instar larvae by ammonium sulfate precipitation and Phenyl-Sepharose and Q-Sepharose column chromatographies. The protein has two subunits, an M_r 84,000 subunit (α) and an M_r 80,000 subunit (β), and the native protein was composed of a heterohexamer (α₃β₃). The two subunits have similar amino acid compositions, with high contents of aromatic amino acids (about 15% phenylalanine plus tyrosine) and low levels of methionine. The N-terminal amino acid sequences of both subunits showed high homologies with insect arylphorin-type storage proteins. The protein concentration in the hemolymph increased steeply from day 3 final instar larva and reached a maximum level of 42 mg/ml in females and 41 mg/ml in males among wandering larvae. The concentration in the hemolymph declined once during the larval–pupal transformation but remained high during the early–mid pupal period and almost disappeared after adult emergence. These quantitative changes were the same for males and females. Based on these characteristics, we identified the hemolymph protein as an arylphorin-type storage protein.     

A new plant virus from the high jungle of the Eastern Andes; Solanum apical leaf curling virus (SALCV)

A previously undescribed plant virus, Solanum apical leaf curling virus (SALCV), was found in cultivated potato and indigenous wild solanaceous plants in an area of high jungle near San Ramon, Peru. Symptoms in potato consisting of red, purple or pink discoloration, curling, crinkling and dwarfing of apical leaves develop soon after infection. Symptoms from tuber-borne infection may also include dwarfing and stunting, dormancy may be prolonged and sprouts may be filiform producing small plants with very thin stems. The virus is transmissible by grafting, but was not transmitted through seed, by aphids or leafhoppers tested, nor by mechanical inoculation of sap. Infected Datura tatula and D. stramonium, the most useful indicator hosts, developed yellowing of the small veins of newly formed leaves followed by distortion, dwarfing, and cupping of subsequently formed leaves. Tomato, Solanum nigrum, Nicandra physalodes and Nicotiana benthamiana were also infected experimentally. N. physalodes, Solanum basendopogon, D. tatula and Physalis peruviana were naturally infected in the field. Antiserum produced in rabbits was suitable for ELISA which detected SALCV in a range of graft-inoculated and naturally infected plants. Most virus particles in purified preparations and those trapped on antiserum sensitised grids treated with infective sap were c. 52 times 17 nm and consisted of three quasi-isometric units in a straight chain. This particle morphology although novel, suggests possible affinities with geminiviruses.     

Structure and characterization of a cDNA clone for phenylalanine ammonia-lyase from cut-injured roots of sweet potato

A cDNA clone for phenylalanine ammonia-lyase (PAL) induced in wounded sweet potato (Ipomoea batatas Lam.) root was obtained by immunoscreening a cDNA library. The protein produced in Escherichia coli cells containing the plasmid pPAL02 was indistinguishable from sweet potato PAL as judged by Ouchterlony double diffusion assays. The M_r of its subunit was 77,000. The cells converted [¹⁴C]-l-phenylalanine into [¹⁴C]-t-cinnamic acid and PAL activity was detected in the homogenate of the cells. The activity was dependent on the presence of the pPAL02 plasmid DNA. The nucleotide sequence of the cDNA contained a 2121-base pair (bp) open-reading frame capable of coding for a polypeptide with 707 amino acids (M_r 77, 137), a 22-bp 5′-noncoding region and a 207-bp 3′-noncoding region. The results suggest that the insert DNA fully encoded the amino acid sequence for sweet potato PAL that is induced by wounding. Comparison of the deduced amino acid sequence with that of a PAL cDNA fragment from Phaseolus vulgaris revealed 78.9% homology. The sequence from amino acid residues 258 to 494 was highly conserved, showing 90.7% homology.     

Synergistic interactions of begomoviruses with Sweet potato chlorotic stunt virus (genus Crinivirus) in sweet potato (Ipomoea batatas L.)

Three hundred and ninety‐four sweet potato accessions from Latin America and East Africa were screened by polymerase chain reaction (PCR) for the presence of begomoviruses, and 46 were found to be positive. All were symptomless in sweet potato and generated leaf curling and/or chlorosis in Ipomoea setosa. The five most divergent isolates, based on complete genome sequences, were used to study interactions with Sweet potato chlorotic stunt virus (SPCSV), known to cause synergistic diseases with other viruses. Co‐infections led to increased titres of begomoviruses and decreased titres of SPCSV in all cases, although the extent of the changes varied notably between begomovirus isolates. Symptoms of leaf curling only developed temporarily in combination with isolate StV1 and coincided with the presence of the highest begomovirus concentrations in the plant. Small interfering RNA (siRNA) sequence analysis revealed that co‐infection of SPCSV with isolate StV1 led to relatively increased siRNA targeting of the central part of the SPCSV genome and a reduction in targeting of the genomic ends, but no changes to the targeting of StV1 relative to single infection of either virus. These changes were not observed in the interaction between SPCSV and the RNA virus Sweet potato feathery mottle virus (genus Potyvirus), implying specific effects of begomoviruses on RNA silencing of SPCSV in dually infected plants. Infection in RNase3‐expressing transgenic plants showed that this protein was sufficient to mediate this synergistic interaction with DNA viruses, similar to RNA viruses, but exposed distinct effects on RNA silencing when RNase3 was expressed from its native virus, or constitutively from a transgene, despite a similar pathogenic outcome.     

Incorporation of Streptidine-C6-phosphate into Phosphorylated Streptomycin by Resting Cell of Streptomyces griseus

The Kunitz-type trypsin inhibitors, ETIa and ETIb, and chymotrypsin inhibitor ECI were isolated from the seeds of Erythrina variegata. The proteins were extracted from a defatted meal of seeds with 10 mM phosphate buffer, pH 7.2, containing 0.15 M NaCl, and purified by DEAE-cellulose and Q-Sepharose column chromatographies. The stoichiometry of trypsin inhibitors with trypsin was estimated to be 1:1, while that of chymotrypsin inhibitor with chymotrypsin was 1:2, judging from the titration patterns of their inhibitory activities.

The complete amino acids of the two trypsin inhibitors were sequenced by protein chemical methods. The proteins ETIa and ETIb consist of 172 and 176 amino acid residues and have M_r 19,242 and M_r 19,783, respectively, and share 112 identical amino acid residues, which is 65% identity. They show structural features characteristic of the Kunitz-type trypsin inhibitor (i.e., identical residues at about 45%) with soybean trypsin inhibitor STI). Furthermore, the trypsin inhibitors show a significant homology to the storage proteins, sporamin, in sweet potato and the taste-modifying protein, miraculin, in miracle fruit, having about 30% identical residues.     

Characterization of a glycoprotein isolated from a continuous tumor-cell line of human lung carcinoma

A glycoprotein with a molecular weight of 62 000 has been isolated from a tumor-cell line, A549, and purified to homogeneity by gel chromatography. The glycoprotein contained sialic acid, galactose, mannose, N-acetylglucosamine and a relatively high amount of glutamic acid and proline. The data indicated that the overall composition of this glycoprotein was different from that of the glycoprotein of M_r 62 000 isolated from lung lavage of patients with alveolar proteinosis. The glycoprotein did not react with the antiserum from lung lavage of patients with alveolar proteinosis. The glycoprotein did not react with the antiserum raised against glycoprotein of M_r 62 000 isolated from lung lavage of patients with alveolar proteinosis.     

The occurrence of maize mosaic virus on sorghum in India1

A leaf disease of sorghum (Sorghum bicolor) characterised by fine discontinuous chlorotic streaks between the veins, was observed on sorghum grown during the 1987/88 post-rainy season in peninsular India. Early-infected plants were stunted, had shortened internodes, and produced poorly developed panicles. The virus was transmitted by the delphacid planthopper, Peregrinus maidis. Negatively stained leaf dip preparations contained bullet-shaped virus particles (208 ± 4.4 × 66 ± 1.0 nm) resembling those of rhabdoviruses. In ultrathin sections, the particles budded through the inner nuclear membrane and were present in the cytoplasm within membrane-bound vesicles that were apparently contiguous with the distended outer nuclear membrane. A method for purifying the virus was developed utilising polyethylene glycol (PEG) precipitation, Celite filtration and sucrose densitygradient centrifugation. An antiserum was produced in rabbits with a titre of 1/2650 in the precipitin ring interphase test. The virus could be detected in infected sorghum leaf tissues using a direct antigen coating form of enzyme-linked immunosorbent assay (DAC-ELISA). In immuno-double diffusion tests, the virus reacted positively with antisera to maize mosaic virus (MMV) from Reunion (MMV-RN) and Hawaii (MMV-HI), but not with antisera to barley yellow striate mosaic (BYSMV), cereal chlorotic mottle (CCMV), and cynodon chlorotic streak (CCSV) viruses. Thus, the virus isolated from sorghum is designated the MMV-S isolate. In DAC-ELISA tests, MMV-S reacted positively with antisera to MMV-R, MMV-HI, MMV-Florida isolate, CCSV, and CCMV, and weakly with antiserum to BYSMV. SDS-polyacrylamide gel electrophoresis revealed four major proteins of relative mass M_r 70 000, 59 000, 32 000 and 28 000. In electro-blot immunoassay, MMV and CCSV antisera detected the G and N proteins. These data suggest that MMV-S should be placed in the sonchus yellow net virus subgroup of plant rhabdoviruses.     

Properties of cherry ring mottle, a distinctive strain of prune dwarf virus

A virus was transmitted from sweet cherry trees with cherry ring mottle disease to cucurbitaceous plants with the aid of liquid nitrogen, caffeine or polyethylene glycol, which were more effective than sodium diethyldithiocarbamate, polyvinylpyrrolidone and other materials used in sap-transmission studies. The virus was transmitted from dormant buds, petals, young leaves, anthers and pollen. Of 172 herbaceous species and varieties tested, twenty-five (thirteen spp.) became infected with virus. Ribes nigrum and peach seedlings were also infected. Of the systems produced in woody plants, those in Italian Prune resembled the symptoms caused by prune dwarf virus, but those in other Prunus spp. did not. In cucumber extracts the thermal inactivation point was between 40 and 44 d?C; dilution end-point was 1/16 to 1/32 and longevity in vitro 8–16 h. Formaldehyde (4%) fixed the particles and preserved their shape for electron microscopy; they were spherical, with a mean diameter of 24 nm. The virus reacted with prune dwarf virus antiserum but differed in several ways from other isolates     

Phosphorylation of the Mr = 34,000 protein in normal and Rous sarcoma virus-transformed rat fibroblasts

Antiserum was raised against the M_r = 34,000 chick cell protein which may serve as a substrate for the Rous sarcoma virus transforming gene product. The antiserum specifically immunoprecipitated 2 proteins from [³⁵S]methionine labeled Rous sarcoma virus-transformed rat cell extracts (a M_r = 35,000 and a M_r = 38,000 protein). Partial protease treatment revealed these two proteins to be very closely related. The protein of apparent M_r = 38,000 was phosphorylated and the phosphate was present exclusively on tyrosine residues. The effect of epidermal growth factor on phosphorylation of the M_r = 35,000 protein was examined in several normal rat fibroblast cell lines. EGF treatment had no effect on phosphorylation of the M_r = 35,000 protein for any normal cell line and also failed to elevate overall levels of phosphotyrosine.     

过表达IbOr基因甘薯增强抗旱性的生理机制

以超表达甘薯橙色基因(IbOr)的转基因甘薯(TS)以及非转基因甘薯(NT)为实验材料,通过15%聚乙二醇6000(PEG-6000)模拟干旱条件,研究转基因与非转基因甘薯幼苗在水分胁迫不同时间的光合系统,膜脂过氧化及抗氧化防御系统中主要指标的变化情况,探讨转基因甘薯耐旱性的生理机制。结果显示:(1)随PEG-6000胁迫时间延长,甘薯叶片的叶绿素、类胡萝卜素含量及其叶片净光合速率、气孔导度、胞间CO2浓度、蒸腾速率都显著降低,但转基因株系降低幅度小于非转基因植株。(2)在正常供水和水分胁迫下,超表达IbOr基因甘薯叶片中O-·2、MDA含量均低于非转基因甘薯,即转基因甘薯具有较低的活性氧水平且脂膜受损伤较小。(3)PEG-6000胁迫24h后,甘薯叶片中SOD、POD酶活性均增加,48h达到最大值,且转基因甘薯中2种酶活性显著高于非转基因甘薯。研究表明,过表达IbOr基因可以有效减轻甘薯在水分胁迫条件下受损害的程度,且可能主要通过提高甘薯的抗氧化胁迫能力来完成。     

Narcissus latent, a virus with filamentous particles and a novel combination of properties

As previously reported, narcissus latent virus (NLV) has flexuous filamentous particles measuring c. 650 nm × 13 nm, is manually transmissible to Nicotiana clevelandii and Tetragonia expansa, and is transmitted by the aphid Myzus persicae following brief acquisition access periods. In contrast to previous reports the virus particle protein has an apparent mol. wt of c. 45 kD. Moreover, infected cells in N. clevelandii leaves contain cytoplasmic inclusion bodies resembling those of potyviruses. In vitro translation of NLV RNA produced only one major product (mol. wt c. 25 kD) which was not precipitated by antisera to virus particle protein or to cytoplasmic inclusion protein. Antisera to 12 potyviruses and nine carlaviruses failed to react with sap containing NLV particles. Similarly antiserum to NLV particles did not react with particles of seven potyviruses or four carlaviruses. A weak reaction was detected between NLV particles and antiserum to particles of maclura mosaic virus (MMV), a virus which resembles NLV in particle morphology and particle-protein size, and in inducing pinwheel inclusions. The cytoplasmic inclusion proteins (CIPs) of NLV, MMV and from narcissus plants with yellow stripe symptoms were serologically inter-related. These proteins were also serologically related to, and had mol. wt similar to, the CIP of members of the potyvirus group. Particles with the size and antigenic specificity of those of NLV were found consistently in narcissus plants with yellow stripe disease. Narcissus latent and narcissus yellow stripe viruses therefore seem to be synonymous and, together with MMV, have properties distinct from those of any previously described virus group.