Abstract:
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
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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.
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