Salicylic acid (SA) treatment triggers inhibition of replication or movement of several positive-sense RNA plant viruses in tobacco. This resistance can also be stimulated by nonlethal concentrations of cyanide and antimycin A (AA) without triggering induction of pathogenesis-related PR-1 protein genes. In two ecotypes of Arabidopsis thaliana (Columbia and Nössen), SA-induced resistance to a tobamovirus, Turnip vein clearing virus (TVCV), was also induced by nonlethal concentrations of cyanide and AA without concomitant induction of PR-1 gene expression. Furthermore, chemically induced resistance to TVCV, as well as the induction of the plant mitochondrial alternative oxidase (a potential target for the chemicals), was independent of NPR1, a gene that plays a key role downstream of SA in the induction of PR proteins. The chemically induced resistance to TVCV appeared to be due to inhibition of replication at the site of inoculation. Taken together, these results show that in Arabidopsis, as in tobacco, resistance to viruses can be induced via a distinct branch of the defensive signal transduction pathway. This suggests that the existence of this virus-specific branch may be widespread among plants.
The technique due to Vincett has been developed to extend previous measurements of the dielectric loss tangent of polyethylene at cryogenic temperatures upwards in frequency to 100 MHz. A second relaxation peak, centred at 4 MHz, found in oxidized polyethylene is both broader and larger than the well-documented peak at 3 kHz. The dielectric loss is changed by steaming in D 2 O and H 2 O vapour at elevated temperatures. In all cases the 3 kHz relaxation is removed. Steaming in D 2 O moves the 4 MHz peak to 30 kHz and subsequent steaming in H 2 O restores it, indicating that there is an interchange of labile hydrogen and deuterium atoms at the site of the dipoles. Subsequent drying in vacuo of polyethylene treated in D 2 O also partially restores the 4 MHz peak, suggesting a further secondary diffusion process. The magnitude of the loss in Rigidex 50 (high-density polyethylene) shows little temperature variation between 1.5 and 4.2 K, while the frequency of maximum loss varies linearly with temperature for the 30 kHz peak; there is, however, a small deviation from linearity at 1.5 K for the 4 MHz peak. The results are analysed in terms of phonon-assisted tunnelling of a particle between two nearly-equivalent potential wells, using exact solutions of Pauling’s cosine model. Tentative estimates of the parameters of the model indicate that the results can be explained by 180° rotation of the proton in a dipolar group of bond length 0.11 nm.
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