Resistance Mechanism of Cultured Plant Cells to Tobacco Mosaic Virus

In somaclonal tissues obtained from systemically TMV-infected tobacco plants, a relation between changes of TMV amounts and the callus growth was examined. The culture medium was suitable for maintaining a constant concentration of TMV as well as active callus growth. By using the shake-culture method, somaclonal tissues were separated into two classes on the basis of callus sizes. In large callus tissues, TMV amounts were constant during subculturing but the tissues did not either grow or release the newly divided cells after the last subculture. On the other hand, smaller callus tissues grew markedly and the TMV amounts were conspicuously lowered. After shake-subculture of smaller tissues, they were successfully regenerated to plantlets. None of the plantlets expressed any mosaic symptoms, while plantlets from the original somaclones showed severe mosaic symptoms of TMV in leaflets. Thus, the present report describes the successful production of virus-free plantlets from infected somaclonal callus cultures.     

植物代谢工程在活性天然产物制备中的应用

本文分析了目前应用植物代谢工程在提高活性天然产物产量方面的研究成果,讨论了植物代谢工程的应用前景。     

Antiviral Effect of Theaflavins on Tobacco Mosaic Virus

Theaflavins, the oxidized products formed from tea leaf catechins during black tea fermentation, showed an antiviral activity on TMV. From the survey of the interactions of theaflavins with RNA and its related substances, it was presumed that theaflavins disturbed the replication cycle of TMV through binding to TMV-RNA.     

Acquired Resistance in Hypersensitive Tobacco against Tobacco Mosaic Virus, Induced by Plant Cell Wall Components

Isolated cell walls from Nicotiana tabacum L. cv. Xanthi-nc were partially digested with enzymes present in the fungal preparation cellulase Onozuka R-10. Released carbohydrate material was separated from the enzymes by gel filtration and fractions were injected into the intercellular spaces of one half of each of several Xanthi-nc leaves. Two to three days after injection the whole leaves were inoculated with TMV. A large reduction in mean lesion diameter was observed in the injected areas compared with those in untreated tissue.     

The Effect of Light on Tobacco Mosaic Virus (TMV) Formation

Discs were punched from TMV-inoculated tobacco leaves (Nicotiana tabacum L.) and illuminated while floating on half strength Vickery's solution maintained at 24°C. After 48 hours some discs were placed in the dark for 24 hours and the amount of TMV formed in the light and dark compared. Discs from young leaves formed more virus in the light than in the dark. Discs from older leaves produced less virus, but as much in the dark as in the light.     

Effect of Tobacco Mosaic Virus on Phospholipid Content and Phospholipase D Activity in Tobacco Leaves

The phospholipid content and phospholipase D activity in the leaves of two tobacco (Nicotiana tabacum L.) cultivars were investigated. These cultivars are characterized by different response to the infection with tobacco mosaic virus (TMV). In the infected leaves of a susceptible cv. Samsun, phospholipid content and phospholipase D activity did not change within seven days after TMV infection. The development of a hypersensitive response in the leaves of a resistant cv. Xanthy necrotic was not accompanied by a change in the total phospholipid content as compared to the noninfected leaves. However, the appearance of necrotic lesions and their subsequent expansion resulted in a steady decrease in the level of phosphatidylglycerol in infected leaves. At the same time, phosphatidic acid and diphosphatidylglycerol contents increased. Leaf zones remote from the regions of necrosis development were also characterized by an increased level of phosphatidic acid. There was a tendency for an increase in phospholipase D activity in both the sites of necrosis development and in the leaf regions remote from these sites. The changes in phosphatidic acid content were of similar nature, and therefore a relative increase in phosphatidic acid could result from the phospholipase D activity. This fact suggests a possible involvement of phospholipase D in the development of the hypersensitive response, and this suggestion is supported by a higher enzyme activity in the leaves of healthy plants of the resistant cultivar as compared to the susceptible one. Causes for the changes in the content of some phospholipids, as well as the physiological role of phospholipase D in the hypersensitive response are discussed.     

Effect of Salicylic Acid and Phenylserine on the Hypersensitive Reaction of Tobacco to Tobacco Mosaic Virus

Injection of leaves of tobacco (Nicotiana tahacum cv. ‘Xanthi’ nc) with salicylic acid (SA) or phenylsene (PS) had an effect on the local lesion development caused by tobacco mosaic virus (TMV), depending upon the concentration used and the time interval between injection and challenge inoculation. Maximum reduction in lesion size was obtained with 0.75 mM SA or with 8 mM PS. Concentrations higher than 1 mM SA or 25 mM PS damaged the leaf tissue, PS being far less toxic than SA. The leaves responded rapidly to injection with SA or PS. A time interval of only 1 h between injection and TMV inoculation reduced the lesion size significantly. Isolated tobacco cell walls incubated with SA yielded carbohydrate fractions capable of reducing lesion size significantly after injection. Cell walls incubated without SA or with PS did not yield active carbohydrate fractions.     

Plant Disease and the Regulation of Enzymes Involved in Lignification: Increased Rate of De Novo Synthesis of the Three Tobacco O-Methyltransferases during the Hypersensitive Response to Infection by Tobacco Mosaic Virus

The mechanism underlying the increase of activity of the three O-methyltransferases of tobacco (Nicotiana tabacum) after infection by tobacco mosaic virus (TMV) has been investigated with a density-labeling method. The three O-methyltransferases from healthy or TMV-infected leaves fed with H₂O or ²H₂O were purified by ion-exchange chromatography and their mean buoyant densities were calculated from their respective distribution profiles after centrifugation to equilibrium on RbCl gradients. Densities were corrected with respect to the mean buoyant density of a radioactive density marker prepared from tobacco leaves floated on a solution containing l-[³H]leucine and selected on a preparative gradient for its density close to those of the O-methyltransferases. The introduction of ²H into the pool of amino acids from which the enzymic proteins were synthesized was monitored. By measurement of the labeling of β-galactosidase synthesized by bacteria from the plant amino acids, it was shown that infection did not alter the rate of labeling of the pool of amino acids. The buoyant-density values of the three O-methyltransferases were determined, and density-labeled enzymes from healthy and infected materials were compared. The largest density shifts from the native enzyme were measured for O-methyltransferases from infected leaves. These results show that the increase in activity of the three enzymes after infection is due to the stimulation of the rate of de novo synthesis of enzyme proteins.     

外壳蛋白羧端序列缺失对烟草花叶病毒侵染性的影响

对野生型烟草花叶病毒(TMV-U1)的外壳蛋白羧端序列进行系列缺失突变,观察到TMV-U1株系的外壳蛋白羧端序列缺失6个氨基酸(保留152个氨基酸),仍能较强系统侵染烟草并高水平表达外壳蛋白,且能在新生叶里复制大量完整的病毒粒子。该研究结果表明：外壳蛋白羧端6个氨基酸序列并非烟草花叶病毒感染和复制所必需,并对利用外壳蛋白羧端缺失型病毒载体表达外源多肽具有一定的启示性。     

Humans Have Antibodies against a Plant Virus: Evidence from Tobacco Mosaic Virus

Tobacco mosaic virus (TMV), a widespread plant pathogen, is found in tobacco (including cigarettes and smokeless tobacco) as well as in many other plants. Plant viruses do not replicate or cause infection in humans or other mammals. This study was done to determine whether exposure to tobacco products induces an immune response to TMV in humans. Using a sandwich ELISA assay, we detected serum anti-TMV antibodies (IgG, IgG1, IgG3, IgG4, IgA, and IgM) in all subjects enrolled in the study (20 healthy smokers, 20 smokeless-tobacco users, and 20 non-smokers). Smokers had a higher level of serum anti-TMV IgG antibodies than non-smokers, while the serum level of anti-TMV IgA from smokeless tobacco users was lower than smokers and non-smokers. Using bioinformatics, we also found that the human protein TOMM40L (an outer mitochondrial membrane 40 homolog – like translocase) contains a strong homology of six contiguous amino acids to the TMV coat protein, and TOMM40L peptide exhibited cross-reactivity with anti-TMV antibodies. People who smoke cigarettes or other tobacco products experience a lower risk of developing Parkinson’s disease, but the mechanism by which this occurs is unclear. Our results showing molecular mimicry between TMV and human TOMM40L raise the question as to whether TMV has a potential role in smokers against Parkinson’s disease development. The potential mechanisms of molecular mimicry between plant viruses and human disease should be further explored.     

Effect of Chemicals on the Early Stages of Tobacco Mosaic Virus Protein Polymerization

Osmotic pressure and sedimentation velocity techniques have been used to investigate the effect of KSCN, thiourea, EDTA, acetamide, and sucrose on the 53,000 molecular weight A protein at pH 6.5-7.0. In the presence of all the compounds except thiocyanate, the number average molecular weight lies between 50,000 and 56,000 which corresponds to a trimer of three chemical subunits. In the presence of thiocyanate, the molecular weight decreases initially sharply with increasing concentration of thiocyanate to 0.1 M, then dissociation proceeds with less efficiency with increasing concentration of KSCN until a molecular weight close to a monomer (21,700) is obtained at 0.59 M KSCN. Sedimentation data agree with osmotic pressure data since, in the absence of thiocyanate, the measured values of S_20,w indicate that the favored state is that of a trimer. In the presence of thiocyanate, however, S_20,w decreases with thiocyanate concentration to S_20,w = 1.9, which is the value reported for the monomer.