Fatty Acid composition in tobacco I. Green tobacco plants

The major fatty acids (16 and 18 carbons) in leaves, flowers, and seeds of Nicotiana tabacum L. cv. Catterton have been analyzed at various intervals during the growth period. From the pattern of their accumulation and relative distribution, it was found that A) the amount of fatty acids in upper young leaves attained a maximum about 75 days after transplanting which is the time of early flowering, while in older leaves the fatty acids continuously declined; B) the relative amount of linolenic acid (18:3) increased progressively with leaf development, from 30% at an early stage to 60% at maturity, while other fatty acids (18:2, 18:1, 18:0, and 16:0) decreased during the same period, indicating a progressive desaturation; and C) a rapid increase of fatty acids was found as flowers developed into seedpods, particularly of linoleic acid (18:2), which comprises 75% of tobacco seed oil.

Air-curing resulted in a loss of fatty acids, especially the unsaturated ones.

     

Polyacrylic acid-induced resistance to tobacco mosaic virus in tobacco cv. Xanthi

Polyacrylic acid (PA) of molecular weight 1700A, 1700B and 3500 caused resistance to infection with tobacco mosaic virus in tobacco cv. Xanthi-nc, when sprayed on the leaves or watered into the soil. The numbers of lesions produced in the treated plants were between 27 and 97% fewer than in the untreated plants depending on the concentration of PA, its molecular weight and the method of application. Some resistance was caused against potato virus X and potato virus Y but only at concentrations that were harmful to the plants. It appears that PA activates a mechanism responsible for localizing viruses in hypersensitive plants.     

Local and systemic spread of tobacco mosaic virus in transgenic tobacco.

Expression of a chimeric gene encoding the coat protein (CP) of tobacco mosaic virus (TMV) in transgenic tobacco plants confers resistance to infection by TMV. We investigated the spread of TMV within the inoculated leaf and throughout the plant following inoculation. Plants that expressed the CP gene [CP(+)] and those that did not [CP(-)] accumulated equivalent amounts of virus in the inoculated leaves after inoculation with TMV-RNA, but the CP(+) plants showed a delay in the development of systemic symptoms and reduced virus accumulation in the upper leaves. Tissue printing experiments demonstrated that if TMV infection became systemic, spread of virus occurred in the CP(+) plants essentially as it occurred in the CP(-) plants although at a reduced rate. Through a series of grafting experiments, we showed that stem tissue with a leaf attached taken from CP(+) plants prevented the systemic spread of virus. Stem tissue without a leaf had no effect on TMV spread. All of these findings indicate that protection against systemic spread in CP(+) plants is caused by one or more mechanisms that, in correlation with the protection against initial infection upon inoculation, result in a phenotype of resistance to TMV.     

Phenylalanine ammonia-lyase in tobacco mosaic virus-infected hypersensitive tobacco. Density-labelling evidence of de novo synthesis.

A strong increase in phenylalanine ammonia-lyase (EC 4.3.1.5) activity occurs in tobacco mosaic virus-infected tobacco leaves developing necrotic local lesions. Comparison of physicochemical properties of the partially purified enzymes extracted from healthy and infected leaves showed that the hypersensitive reaction leads to an increase in the pool size of the same active enzyme molecules as those present in non-infected material. The molecular mechanism of enzyme formation was investigated by radiolabelling with [3H]leucine and by density labelling with 2H2O. Abnormal patterns of incorporation of radioactivity into all soluble proteins were found in infected leaves carrying local lesions. In contrast, uptake of deuterium into the amino acid pool was the same in healthy and infected leaves. Unstimulated phenylalanine ammonia-lyase was shown to be a long-lived enzyme (half-life: 25-35 h). Results of comparative density labelling experiments unequivocally demonstrated that the increased enzyme pool size arose from an increased rate of synthesis mediated by the hypersensitive reaction.     

Neighborhood-based tobacco advertising targeting adolescents.

Adolescent tobacco use remains a serious problem, and adolescents may be particularly receptive to the glamorous images tobacco companies use in advertisements. A relatively new form of neighborhood-based outdoor advertising, the illuminated bus-stop-shelter billboard, was studied to determine tobacco companies'' use of this medium. We hypothesized that in 2 distinct San Francisco, California, neighborhoods, 1 predominantly white and the other mostly Latino, we would find a predominance of tobacco advertising on these billboards in both neighborhoods, that tobacco advertisements would be more prevalent in the minority Latino neighborhood, and that tobacco advertising would target adolescents in both neighborhoods. Each bus-stop-shelter billboard advertisement in the study areas from April 1992 to March 1993 was recorded. The type and frequency of products advertised and qualitative content of tobacco advertisements were analyzed. Adolescents'' possible exposure to these advertisements was noted. Our main outcome measures were the percentage of tobacco advertising, possible adolescent exposure to this advertising, and themes of the tobacco advertisements. About 10% of all bus-stop-shelter billboard advertisements in each area promoted tobacco use. Possible exposures to these advertisements were greater in the Latino neighborhood because of a greater adolescent population. Qualitative analyses of tobacco advertisements suggested that adolescents are the primary targets. We urge physicians and educators to explicitly address this form of tobacco advertising, and we urge a ban on neighborhood-based tobacco advertising.     

Assembly of tobacco mosaic virus.

The assembly of tobacco mosaic virus requires the presence of a particular protein aggregate, the disk. During the nucleation, a specific region of the RNA interacts with a single disk, to bring about a necessarily cooperative transition from the paired two-layer structure to a short segment of nucleo-protein helix. There is a high selectivity for this region of the TMV RNA, because of the many nucleotides bound at once, and other nucleotide sequences appear only to bind by a different mechanism. Elongation of the nucleated rods can continue with either further disks or the less aggregated 'A-protein' as the protein source, but the continued cooperativity inherent with disks would have some advantages. The rates of the two processes have been separately determined and growth is faster when disks are still present. New experiments show that the breakdown of disks to yield A-protein is relatively slow and it is concluded that virus growth from disks could not proceed through a prior breakdown in solution, but must involve the direct interaction of the disk with the growing nucleoprotein rod. The detailed mechanism of disk addition is not understood but it may involve a directed breakdown, since there is also evidence for the existence of a non-equilibrium form of A-protein which has aggregation kinetics distinct from those of equilibrium A-protein. Some implications for the general assembly pathways of viruses both of the specificity and of the assembly/disassembly cycle during the viral infection are considered.     

Apical dominance in Pssu-ipt-transformed tobacco.

In Pssu-ipt-transformed tobacco, apical dominance was released by defoliation of the upper nodes, while the apex remained intact. After defoliation, the concentration of cytokinins (CKs) increased whereas IAA remained constant, evoking an increase in the CK/IAA ratio in the buds. Moreover, defoliation resulted in a tremendous increase in the concentrations of aromatic amines (AAs): tyramine (TYR), phenethylamine (PEA) and an as yet unidentified compound. Although the total aliphatic monoamine and polyamine (PA) concentration remained constant, putrescine (PUT) and spermidine (SPD) concentrations in the axillary buds decreased, whereas the concentration of spermine (SPM) increased. Similar changes in PAs and AAs could be observed in the buds of untransformed SR1 plants after decapitation, whereas defoliation without removal of the apex had no effect. This is the first report on the possible involvement of PAs and AAs in apical dominance.     

Binding of tobacco mosaic virus to membrane material isolated from tobacco leaves.

Binding of tobacco mosaic virus (TMV) to disrupted tobacco leaf membrane was studied. Membrane isolated from tobacco leaves was treated successively with (NH4)2SO4, Li-diiodosalicylate and then pronase. TMV-binding substance was thus isolated in a soluble form. From enzymatic digestion experiments, it was suggested that the binding substance was composed of lipid and carbohydrate.