2 resultados para Pea enation mosaic virus 1 (PEMV1)

em Brock University, Canada


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STOBBS, Lorne,W ABSTRACT Biochemical and Histological Investigations of viral localisation in the hypersensitive reaction of Phaseolus vulgaris L. var Pinto to tobacco mosaic virus infection. The infection of Phaseolus vulgaris L. var Pinto with tobacco mosaic virus (TMV) results in the production of distinct necrotic lesions confining the virus to restricted areas of the leaf surface. Biochemical and histological changes in the leaf tissue as a result of infection have been described. Trace accumulations of fluorescent metabolites, detected prior to lesion expression represent metabolites produced, by the cell in response to virus infection. These substances, are considered to undergo oxidation and in diffusing into adjacent cells, react with cellular constituents causing the death of these cells. Such cellular necrosis in advance of infection effectively limits virus spread. Chromatographic studies on extracts from TMV infected Pinto bean leaf tissue suggests that a number of extra-fluorescent metabolites produced on lesion'expression represent end products of phenolic oxidation r,eactionsoccurring earlier in these cells. Inhibition of phenolic oxidation by ascorbate infiltration or elevated temperature treatment resulted in the absence of extra-fluorescent metabolites and the continued movement of virus in the absence of necrosis. Further studies with i ascorbate infiltration indicated that irreversible necrotic events were determined as early as 12 tci 18 hrs after viral inoculation. Histochemical tests indicated that callose formation was initiated at this time, and occurred in response to necrotisation. Inhibition of necrosis by either ascorbate infiltration or elevated temp8rature treatment resulted in the absence of callose deposition. Scanning electron'micrographs of infected tissue revealed severe epidermal and palisade cell damage. Histochemical tests indicated extensive callose formation in cells bordering the lesion, and suggested the role of callose iTh the blockage of intercellular connections limiting virus movement. The significance of these cellular changes is discussed. ii

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Polarized reflectance measurements of the quasi I-D charge-transfer salt (TMTSFh CI04 were carried out using a Martin-Puplett-type polarizing interferometer and a 3He refrigerator cryostat, at several temperatures between 0.45 K and 26 K, in the far infrared, in the 10 to 70 cm- 1 frequency range. Bis-tetramethyl-tetraselena-fulvalene perchlorate crystals, grown electrochemically and supplied by K. Behnia, of dimensions 2 to 4 by 0.4 by 0.2 mm, were assembled on a flat surface to form a mosaic of 1.5 by 3 mm. The needle shaped crystals were positioned parallel to each other along their long axis, which is the stacking direction of the planar TMTSF cations, exposing the ab plane face (parallel to which the sheets of CI04 anions are positioned). Reflectance measurements were performed with radiation polarized along the stacking direction in the sample. Measurements were carried out following either a fast (15-20 K per minute) or slow (0.1 K per minute) cooling of the sample. Slow cooling permits the anions to order near 24 K, and the sample is expected to be superconducting below 1.2 K, while fast cooling yields an insulating state at low temperatures. Upon the slow cooling the reflectance shows dependence with temperature and exhibits the 28 cm- 1 feature reported previously [1]. Thermoreflectance for both the 'slow' and 'fast' cooling of the sample calculated relative to the 26 K reflectance data indicates that the reflectance is temperature dependent, for the slow cooling case only. A low frequency edge in the absolute reflectance is assigned an electronic origin given its strong temperature dependence in the relaxed state. We attribute the peak in the absolute reflectance near 30 cm-1 to a phonon coupled to the electronic background. Both the low frequency edge and the 30 cm-1 feature are noted te shift towards higher frequcncy, upon cntering the superconducting state, by an amount of the order of the expected superconducting energy gap. Kramers-Kronig analysis was carried out to determine the optical conductivity for the slowly cooled sample from the measured reflectance. In order to do so the low frequency data was extrapolated to zero frequency using a Hagen-Ru bens behaviour, and the high frequency data was extended with the data of Cao et al. [2], and Kikuchi et al. [3]. The real part of the optical conductivity exhibits an asymmetric peak at 35 cm-1, and its background at lower frequencies seems to be losing spectral weight with lowering of the temperature, leading us to presume that a narrow peak is forming at even lower frequencies.