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Plant Defense Mechanisms
Plants have evolved with mechanisms to both tolerate and actively defend
themselves against attack from herbivores and pathogens. The attackers have
also evolved counter-intelligence capabilities. We are studying the
communication processes that coordinate these responses. The current
emphasis is on the role of jasmonate, a plant hormone and signaling
component in the chain of metabolic defense responses. Research strategies
include:
- Observing transport and binding of photoassimilate in response to
challenge by jasmonate and herbivory
(See
article)
- Designing radioligands and using them to observe signal transport
and perception (eg methyl jasmonate). (See
article)
Volatile organic compounds
A significant fraction of the carbon assimilated by some plants—poplars,
for example—is returned to the atmosphere as volatile organic compounds
(VOC) which act as greenhouse gases, and can influence the radiative balance
of the atmosphere even more severely than carbon dioxide. We are studying
the emission from poplar of the VOC isoprene. It is highly variable, derives
from very recently acquired carbon, and is stimulated by a plant hormone
that is deeply invloved plant defense. These significant environmental and
developmental effects need to be understood for us to anticipate
consequences of any changes in ecosystems for the environment. (see
Plant Cell & Environment article)
Phytoremediation
Plants
have a valuable role in helping to clean up polluted water and soil. Flows
of polluted groundwater can be restricted, nutrients for soil bacteria are
provided, and many pollutants are taken up. We are studying the
phytoremediation of carbon tetrachloride. Plants take up this volatile
carcinogen and convert some of it to a less volatile and more benign
material. By radiolabelling the pollutant we are studying its uptake and
metabolism. We find for example that plant stress caused by the pollutant is
relieved by prior exposure to the hormone jasmonate (see
poster, PDF).
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Methyl jasmonate increases both plant tolerance
to carbon tetrachloride in soil solution, and also bioconversion of
this volatile and carcinogenic pollutant to TCA (trichloroacetic
acid: benign and involatile). |
Biological activity
A critical structure in biological organisms is the lipid membrane, which
has several distinct roles, including compartmentation so that specific
chemical interactions can be regulated, a facility for extracting work by
converting energy between chemical, electrical and mechanical forms, the
generation of osmotic pressures for transport and structural strength.
- Non-invasive imaging, which gives us a direct in vivo measure of
membrane transport, is being used to quantify the biological effect of a
range of chemicals and nanostructures with engineered biological
functionality.
Nitrogen transport
Nitrogen is a limiting resource in many ecosystems. We are studying
uptake of nitrate and ammonia by roots and transport within the plant, as
well as transport of amino acids which are synthesized in many plant
tissues, using nitrogen-13.
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Phloem transport of amino acids Transport
in aspen sapling of radioactive nitrogen, administered as ammonia to
a mature leaf. Movement towards the roots is interrupted by chilling
the stem. Because we know chilling affects transport in phloem but
not in xylem, the data show that nitrogen is carried by phloem
transport. |
Last Modified: February 1, 2008
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