Interactions between tobacco mosaic virus and the tobacco N gene

The interaction between tobacco mosaic virus (TMV) and tobacco harbouring the N gene is a classical system for studying gene-for-gene interactions in disease resistance. The N gene confers resistance to TMV by mediating defence responses that function to limit viral replication and movement. We isolated the N gene and determined that N belongs to the nucleotide-binding-site-leucine-rich-repeat (NBS-LRR) class of plant disease resistance genes, and encodes both full-length and truncated proteins. Sequence homologies and mutagenesis studies indicated a signalling role for the N protein similar to that seen for proteins involved in defence responses in insects and mammals. The N gene confers resistance to TMV in transgenic tomato, demonstrating the use of the NBS-LRR class of disease resistance genes in engineering crop resistance. From the pathogen side of this interaction, the TMV 126 kDa replicase protein has been implicated as the avirulence factor that triggers N-mediated defence responses. We employed Agrobacterium-mediated expression strategies to demonstrate that expression of the putative helicase region of the replicase protein is sufficient to elicit N-mediated defences. The thermosensitivity of the N-mediated response to TMV is retained when induced by expression of this replicase fragment. Thus, both components of this gene-for-gene interaction are now available for studies that address the molecular mechanisms involved in N-mediated TMV resistance.     

烟草对烟粉虱的抗性与烟草化学成分的相关性

为探明烟草对烟粉虱Bemisia tabaci(Gennadius)的抗性机制,分别测定了不同烟草品种的叶绿素相对含量、鲜烟叶及烤后烟叶的化学成分含量,并分析了烟草抗虫性与烟草化学成分的关系.结果表明,中部叶片叶绿素含量与烟粉虱数量呈负相关,相关系数达到了显著水平;鲜烟叶化学成分钾氯比、糖碱比、氮碱比、还原糖、烟碱、蛋...     

Effect of tobacco mosaic virus strains on the ultrastructure of tobacco leaf parenchymal cells

Accumulation of considerable amounts of viral particles has been demonstrated in parenchymal cells of young leaves in tobacco cultivar Samsun systemically infected with any of studied tobacco mosaic virus (TMV) strains isolated from pepper (TMV-p), tomato (TMV-t), and eggplant (TMV-e). Abnormal (swollen and thin) virions were found, which points to their destruction. Cell infection with all studied strains was accompanied by the activation of the lysosomal compartment manifested as formation of nascent dictyosomes, elements of smooth endoplasmic reticulum, cytoplasmic vacuoles, various vesicles, invaginated mitochondria, and multivesicular bodies. The studied viral strains could be arranged in the following sequence according to the degree of lysosomal compartment stimulation and induction of intracellular lytic processes mediating the destruction of viral particles and cell structures: TMV-p > TMV-e > TMV-t.     

Enzymes of the phenylpropanoid pathway and the necrotic reaction of hypersensitive tobacco to tobacco mosaic virus

Pronounced increases in activity of phenylalanine ammonia-lyase (PAL), cinnamic acid-4-hydroxylase (CAH) and caffeic acid-O-methyltransferase (OMT)     

Biosynthesis of tobacco mosaic virus RNA in tobacco protoplasts

Changes in the number of protoplasts, viability, protein and chlorophyll contents and ribonucleases activity were studied in tobacco mesophyll protoplastsin vitro inoculated with tobacco mosaic virus (TMV). The number of protoplasts slowly increased during the cultivation period and the viability decreased from 95 to 67% in the control noninoculated protoplasts, and to 55% in the infected protoplasts. 30 h after inoculation the protein and chlorophyll contents strongly decreased to 25–30% and 17–19%, respectively, in comparison with contents 3 h after inoculation. The chlorophylla/b ratio decreased from 2.11 and 2.02 to 0.79 and 0.60 in healthy and infected protoplasts, respectively. The activities of ribonucleases in protoplasts quickly decreased during experiment but they were higher in infected than in noninfected protoplasts (between 20 to 30 h after inoculation they were 132 to 146% higher than that in healthy controls). These activities corresponded to the multiplication curve of TMV.     

Taxes and the tobacco wars

In this issue (see pages 187 to 191) Dr. Vivian H. Hamilton and associates demonstrate that tax reductions introduced in 5 Canadian provinces in 1994 slowed the rate of decline in cigarette consumption in those jurisdictions. Although both reductions and increases in taxation have been shown to influence tobacco consumption, changes in smoking habits must also be understood in the context of battles being waged on other fronts in the tobacco wars. In addition, more finely detailed analyses are needed to determine the impact of taxation and other factors on the smoking habits of specific subgroups of the population, particularly teenagers.     

成熟期光强对烤烟理化特性和致香成分含量的影响

2004、2005年在四川凉山烟科所通过盆栽试验,在烤烟成熟期营造不同的光照强度,研究了成熟期光强不同对烤烟品质的影响。结果表明:成熟期随着光照强度的降低,叶片厚度降低,栅栏组织/海绵组织的比值降低,烤后烟叶单叶重、厚度、叶质重降低,叶片含梗率增加,总糖和还原糖含量降低,总氮和烟碱含量升高,钾和氯含量增加,叶黄素、β-胡萝卜素和类胡萝卜素总量增加,中性致香成分含量呈增加趋势,增加到一定程度开始降低。     

Phosphodiesterase activities in transgenic tobacco plants associated with the movement protein of tobacco mosaic virus

Summary Hydrolytic activities of leaf extracts from normal and transgenic plants, with (+ MP) and without (-MP) the movement protein of tobacco mosaic virus, were examined. In the + MP transgenic plants, as compared with non-transgenic and — MP plants, higher hydrolytic activities were found on the following substrates: bis-(nitrophenyl)-phosphate (BPNPP, phosphodiesterase), p-nitrophenyl-(phenyl)-phosphate (PNPPP, nucleotidephosphodiesterase) and thymidine-3-monophosphate p-nitrophenyl ester (T₃MPP; 3nucleotide phosphodiesterase.) The + MP plant lines, as compared with other transgenic plants, exhibited higher nucleotide-phosphodiesterase activity in the soluble as well as in the membrane fraction. Substrate concentration kinetic studies revealed the presence of a nucleotide-phospho-diesterase with a high substrate affinity in the +MP extracts in addition to the enzyme with a relatively low substrate affinity present also in the — MP transgenic plants. This high affinity enzyme could be removed from the soluble fraction by precipitation with anti-MP serum, indicating its possible association with the movement protein.     

Developmental changes in plasmodesmata in transgenic tobacco expressing the movement protein of tobacco mosaic virus

Summary Cell-to-cell communication in plants occurs through plasmodesmata, cytoplasmic channels that traverse the cell wall between neighboring cells. Plasmodesmata are also exploited by many viruses as an avenue for spread of viral progeny. In the case of tobacco mosaic virus (TMV), a virally-encoded movement protein (MP) enables the virus to move through plasmodesmata during infection. We have used thin section electron microscopy and immunocytochemistry to examine the structure of plasmodesmata in transgenic tobacco plants expressing the TMV MP. We observed a change in structure of the plasmodesmata as the leaves age, both in control and MP expressing [MP(+)] plants. In addition, the plasmodesmata of older cells of MP(+) plants accumulate a fibrous material in the central cavity. The presence of the fibers is correlated with the ability to label plasmodesmata with anti-MP antibodies. The developmental stage of leaf tissue at which this material is observed is the stage at which an increase in the size exclusion limit of the plasmodesmata can be measured in MP(+) plants. Using cell fractionation and aqueous phase partitioning studies, we identified the plasma membrane and cell wall as the compartments with which the MP stably associates. The nature of the interaction between the MP and the plasma membrane was studied using sodium carbonate and Triton X-100 washes. The MP behaves as an integral membrane protein. Identifying the mechanism by which the MP associates with plasma membrane and plasmodesmata will lead to a better understanding of how the MP alters the function of the plasmodesmata.Abbreviations MP movement protein - TMV tobacco mosaic virus     

烟草内生菌对烟草根结线虫病的防治效果

从烟草中筛选到几株内生菌进行防治根结线虫的盆栽试验,以研究其防治效果.结果表明,内生细菌发酵液的防治效果优于内生细菌菌体,内生放线菌则相反.内生菌普遍对植物具有促生作用,但内生菌菌体的促生效果优于内生菌的发酵液.H3号内生细菌对根结线虫防治效果最好,病情指数为4.16,防效为91.68%,明显优于对照,优于阿维菌素处理,H3号内生细菌处理的烟草形态指标明显优于阿维菌素处理.

Abstract：

Several tobacco endophyte strains were screened out, and their controlling effect against tobacco root-knot nematodes was studied with pot experiment. The fermentation broth of endophytic bacteria was more effective than the bacterial thallus, while that of endophytic actino-mycetes was less effective than the actinomycete fermentation broth. All test endophytes promoted tobacco growth, and the promotion effect of their thalli was better than that of their fermentation broths. Endophytic bacterial strain H3 was the best in controlling tobacco root-knot nematode dis-ease, with 91.68% controlling effect and a disease index of 4. 16, much better than the treat-ments CK and avermectin. Moreover, the morphological feature of tobacco plant treated with H3 was better than that treated with avermectin.     

On the mutation of the tobacco mosaic virus

Experiments on x-ray-induced mutations of the tobacco mosaic virus (Gowen) are analyzed on the basis of the ionization theory. The size of the volume within which the primary process of mutation develops is calculated on the basis of three alternative assumptions; viz., (1) that this volume consists of protein, (2) that it is nucleic acid, (3) that it is phosphorus. It is found that the volume calculated under assumption (1) is identical with the hexagonal cell unit which Bernal and Fankuchen found in the virus protein by x-ray diffraction. Assumptions 2 and 3 lead respectively to the conclusions that one-fourth of the total nucleic acid content or one-half of the total phosphorus content is involved in the mutational process. The relation between the induced and the spontaneous mutation is examined and it is found that natural ionizing radiations are completely insignificant for the spontaneous mutation of the virus.