The thermotolerance effect of isoprene.
My Ph.D. work answered the question, “Why do
plants make isoprene?” This was the first data
showing that light hydrocarbon emission from plant leaves
was something more than just “wasted carbon”,
as most had previously thought. Subsequent experiments have
confirmed that isoprene gas protects photosynthesis while
leaves reach above 35°C during normal temperature
fluctuations, and that leaf temperature fluctuations are
frequent and large.
Recent evidence indicates that isoprene gas may prevent the
loss of the proton gradient across thylakoid membranes at
high temperatures. Future work in this area will pursue the
behavior of photosynthesis under fluctuating temperatures,
the mechanism of protection, and observations of
temperature fluctuations in natural environments. The
combination of these data may help answer the question of
why some species make isoprene while others do not. I
anticipate that future studies will lead to new discoveries
about high temperature damage to photosynthesis and the
relationship between heat and light tolerance via
energy-dependent chlorophyll fluorescence quenching
mechanisms.
Control of plant hydrocarbon synthesis.
In conjunction with the thermotolerance work, I have
begun working on a metabolic control model of terpene
emissions in higher plants. A useful testbed for this
approach will be to transform organisms that do not produce
isoprene with a clone of the gene for isoprene synthase,
the enzyme responsible for isoprene emission. Addition of
this single gene to Arabidopsis thaliana has produced
plants that emit isoprene. To date, the control of isoprene
synthesis in these transformants has not been
characterized.
Demand control of photosynthesis and acclimation of
elevated CO2.
After working on the physiology of plant acclimation
to elevated CO
2 at the University of Illinois, I
became convinced that further progress in understanding why
plants acclimate to suture climates in some cases and not
in others was limited by the questions typically asked.
This led me to begin developing an approach that helps
describe when plant productivity is limited by light,
CO
2, or by internal growth limitations. I have
developed a model, based on metabolic control analysis,
that allows the determination of these limitations.
Preliminary results obtained from an elevated
CO
2 (FACE) experiment show that plants grown at
elevated CO
2 are more less limited by downstream
demand for light energy (e.g., there’s more demand
for photosynthate) than at ambient CO
2. I hope
to test this model more fully using manipulations of plant
supply and demand relationships.
Stable isotopes and gross ecosystem productivity.
In 2000, I joined a project with the University of
Michigan Biological Station (UMBS) investigating the net
carbon sink of a northern hardwood forest. The group,
composed of boundary-layer meteorologists and ecologists,
invited me to develop stable-isotope techniques to measure
the forest gross primary productivity – equivalent to
the photosynthesis rate of the canopy.
Phytoremediation of soil and groundwater using hybrid
poplar.
I have been working with the UWSP Environmental Task
Force lab in the College of Natural Resources. Members of
this group are operating a field trial of hybrid poplar
trees at a site with high groundwater levels of Dinoseb
(2-
sec-butyl-4,6-dinitrophenol), an herbicide and
pesticide banned in the United States in 1992 due to links
to human birth defects.
In order to more accurately asses the success of
phytoremediation in the field, and to possibly direct
breeding and genetic engineering of plants, my research
program is directed at studying plants’ role in the
breakdown of organic molecules. Some initial data I
collected at a field trial indicate that some hybrid poplar
clones may be more tolerant to Dinoseb contamination than
others. This work nicely integrates my interests in
photosynthetic physiology of thylakoid membranes and tree
canopy processes because 1) Dinoseb may interact with
photosystem II by accepting electrons from the reaction
center, and 2) measurements of water (and hence
contaminant) transport by poplar stands.
We have recently begun to look at the possibility that
remediation is facilitated by organic carbon provided by
plant roots. Future experiments will study the relationship
between aboveground plant productivity, root exudates, and
soil properties contusive to anaerobic metabolism of
pesticides. In a sense, the plants will be used to farm the
soil microorganisms that do most of the remediation.
