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Structural, biochemical and physiological aspects of a systemic virus host interaction

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Boucher, Wayne Desmond (1975) Structural, biochemical and physiological aspects of a systemic virus host interaction. PhD thesis, University of Tasmania.

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Abstract

A Susceptible tobacco variety infected with a mosaic-inducing strain
of tobacco mosaic Virus displayed certain alterations in normal growth
patterns. This work confirmed that such plants, as a result of infection,
were reduced in plant height, internode length and leaf size. Infected
plants also had reduced root systems. The rate of leaf growth., that is
the time taken for leaves to reach full expansion size, was similar for
infected and virus-free plants although the number of leaves formed over
a 6 week period following inoculation was slightly greater for virus
infected plants. Infection of young plants delayed both flower initiation
and the appearance of inflorescences. A reduced rate of cell division
in sub-apical regions appeared to be the major factor in reducing plant
size.
The survival of plant supporting virus synthesis appeared to be related
to certain metabolic changes. Specific enzymes associated with photorespiration
and "dark" respiration had lower activities in Virus infected
plants.
Enzymes indirectly associated with chloroplasts and photosynthetic
pigments were also reduced in virus-containing tissues. To some extent,
the reduced potential of carbon fixation by photosynthesis was offset by
a reduced cellular demand from carbon utilized in photorespiration and
"dark" respiration, this enabling cells to support a level of virus synthesis.
Normal activity of an enzyme associated with the Embden-Mbyerhofparnas
pathway of carbohydrate metabolism higher activity of an enzyme
associated with the pentose phosphate pathway and reduced activity of
an enzyme associated with "dark" respiration suggested that most carbohydrates
moving through the major pathways of metabolism are channelled
towards virus synthesis through conversion to amino acids. The high activity
of hydrolytic enzymes in virus-containing tissues suggested a high
rate of metabolism of carbohydrates and nucleic acids that would be expected
of cells supporting both virus synthesis and cellular metabolism. Two features of virus infected plants ensure their survival: delayed onset of leaf senescence and the presence of virus-free tissues with leaf
mosaics. Biochemical and ultrastructural studies revealed that over-mature
leaves on virus-infected plants were metabolically active and composed
of cells containing intact membrane systems. Most enzymes studied
in similarly aged leaves from uninoculated plants had greatly reduced
activities and cells in these tissues contained membrane components that
showed signs of deterioration and disorganization. Virus-free areas of
mosaic diseased leaves, referred to as dark green island tissues, were
Metabolically more active than comparably aged tissues from uninfected
plants. Enzymes associated with photosynthesis and carbohydrate metabolism
and photosynthetic pigments were at greatest levels in these tissues.
Of the three tissue types compared, virus -containing and virus-free tissues
from infected plants and leaf tissues from uninfected plants, dark
green island tissues had the greatest potential for photosynthesis and
Carbohydrate metabolism.
Growth patterns of virus-infected plants, delayed flower initiation
and onset of leaf senescence, the altered activities of enzymes associated
with chloroplasts and carbohydrate metabolism and the stimulated activities
of enzymes in dark green island tissues suggested that basic responses
of plants to infection occurred through shifts in endogenous
growth regulator levels. Bioassays of the major growth regulators revealec that although a gibberellin A3-like compound was unaffected by infection,
cytokinin-Iike compounds and an indole acetic acid-like compound
were at higher levels in infected tissues and an abscisic acid-like compound
was at a reduced level. The altered balance of the major growth
stimulating and growth retarding hormones is sufficient to account for
most of the measured and observed changes in diseased plants.

Item Type: Thesis (PhD)
Keywords: Tobacco mosaic virus, Host-virus relationships
Copyright Holders: The Author
Copyright Information:

Copyright 1975 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1976. Includes bibliography

Date Deposited: 25 Nov 2014 00:39
Last Modified: 21 Jun 2016 00:08
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