David Dalton's Home Page
 |
Professor of Biology Office: Biology room B242 Portland, OR 97202 email: david.dalton@reed.edu |
 |
You may click on any image on this page to get related links
Education:
1986 Ph.D. Oregon
State University (Botany)
1976 M.S.Oregon State University (Botany)
1973 B.S.Duke University (Botany and Plant Pathology)
I have been at Reed College since
1987. My teaching responsibilities include Plant
Physiology (Biol 322), Introductory
Biology (Biol 101-102) and various seminar courses (Biol
431) such as Forest Canopy Biology, Biological Aspects of Climate
Change, and Environmental Physiology
of Plants. I usually supervise about 4 senior theses each year
on a variety of
topics in plant sciences. Some typical examples include:
Sasha Kramer (1999) Associative Nitrogen Fixation in Temperate Coastal Grasses
Pat Brown (1999)Photosynthesis and Nitrogen Fixation by Lobaria
oregana in an Old-growth Forest Canopy
Alison Hornor (2000) Seasonal and Spatial Variation of Antioxidants
in an Old Growth Pseudotsuga menziesii Canopy
James Mapes (2000) Characterization of Ascorbate Peroxidase and
Glutathione S-Transferase from a Medicago truncatula Root
Nodule cDNA Library
Sarah Klain (2003) The Role of Red Alder (Alnus rubra)
in Ecosystem Management
Jillian De Gezelle (2003) The Contribution of
the Porella/Nostoc Association to the Nitrogen Budget
of an Oregon Old-Growth
Forest
Lisa Fuller (2004) Identification of Glutathione S-Transferase Genes in Soybean (Glycine max) Root Nodules
Jack Kidney (2005) Detection of Antioxidant Gene Expression in Soybean Root Nodules Using Real-time PCR.
Leslie Lilly (2006) The Synergy of the Plant-Microbe Interaction in Selenium Bioremediation
Dan Sullivan (2008) The Use of Two White Rot Fungi - Pleurotus and Trametes -
in the Bioremediation of Used Motor Oil
My thesis students have gone on to various graduate schools
such as : Cornell, OR State Univ, Stanford, Univ. of
GA, Univ. of AZ, UC-Davis, Univ. of UT,
Univ.
of NC-Chapel Hill, Univ. of NE-Lincoln, and Univ. of WA.
Research:
My primary interests are in biological nitrogen fixation and oxygen toxicity. Nitrogen-fixing plants (such as soybean, alfalfa, and alder) convert atmospheric nitrogen into ammonia and ultimately protein so they are partly self-fertilizing. However, this ability does not come without risks since nitrogen-fixing systems are very susceptible to damage from active forms of oxygen such as superoxide and hydrogen peroxide. My students and I have been examining various aspects of the defenses against active oxygen in nitrogen-fixing legume root nodules. We have concentrated on the role of the ascorbate-glutathione pathway which has 4 enzymes.
The research in my lab has been multi-disciplinary, starting first with traditional protein purification and characterization. This allowed us to make antibodies for immunolocalization studies in which we showed that ascorbate peroxidase is cytosolic and particularly enhanced in the endodermis layer of legume nodules. At the whole-plant level, we have shown up-regulation of the ascorbate-glutathione system in response to elevated ambient oxygen and in effective (i.e. capable of nitrogen fixation) as opposed to ineffective nodules. We have also explored the molecular biology of nodule antioxidants. Two of the oxygen defense genes (ascorbate peroxidase and glutathione reductase) have been cloned and sequenced. The peroxidase gene was moved into an E. coli expression system to facilitate the production of large amounts of pure recombinant protein. This allowed us to develop an in vitro reconstitution system ("bionic nodules") containing nitrogen-fixing bacteria, leghemoglobin, and the components of the ascorbate-glutathione system. These "bionic nodules" showed a remarkable 4-fold increase in nitrogen fixation when amended with antioxidants. Suppport for this work has been provided by the National Science Foundation for more than 17 years.
My students and I have also investigated the environmental physiology of antioxidant processes in conifers from the Pacific Northwest. Antioxidant defenses in conifers are a major means by which they deal with environmental stresses such as chilling, strong light, and drought. We are using the Wind River Canopy Crane Research Facility. near Carson, Washington to examine foliage of Douglas-fir and Grand fir at various heights in the old growth canopy to determine how antioxidants vary with respect to season and position in the canopy. Other studies have focused on the important role of nitrogen-fixing lichens (Lobaria oregana) in these canopies.
My lab has also uncovered a novel system of nitrogen fixation in European beachgrass (Ammophila arenaria). We have observed that this grass harbors nitrogen-fixing bacteria living within the cell walls of stems and rhizomes, making this the first known case of endophytic nitrogen fixation by any temperate grass species. We have isolated the bacterium responsible for nitrogen fixation (Burkholderia tropicalis) and are in the process of further characterizing this system using a wide range molecular, biochemical, and ecological approaches. See photomicrograph below.
A. Confocal immunofluorescent image obtained with use of anti-nitrogenase antibodies indicating the presence of nitrogen-fixing bacteria (glowing yellow or blue spots) in the cell walls of beachgrass.
B. Transmission electron micrograph showing immunogold localization of nitrogenase in cell walls of beachgrass.
C. Typical scene on the Oregon coast showing prominent grasses on the sand dunes.
Most recently, we have been exploring the role of glutathione S-transferase (GST) in nitrogen-fixing nodules of soybean. There are 25 GST genes in soybean. The function of GST is unclear, but we postulate that it may be another aspect of the antioxidant defense in nodules. Our initial results with quantitative real-time PCR indicate that the expression of GST9 in nodules is much more enhanced than is the case with other GSTs. This work is being supported by NSF grant IOB 0517688 for 2005-2008.
I also have interests in the ecology and natural history of the West, especially as it relates to the observations of Lewis and Clark. I am the author of a recent book on this topic, entitled The Natural World of Lewis and Clark published by the University of Missouri Press.
 |
I also have
interests in the ecology and natural history of the West, especially
as it relates to the observations of Lewis and Clark. I am the author
of a recent book on this topic, entitled The
Natural World of Lewis and Clark published by the University of
Missouri Press.
|
Selected publications:
(* student co-author)
Dalton, D.A., L. Diaz del Castilo, M. L. Kahn, S. L. Joyner*, and J.M. Chatfield. 1996. Heterologous expression and characterization of soybean cytosolic ascorbate peroxidase. Arch. Biochem. Biophys. 328:1-8.
Dalton, D. A., S. L. Joyner*, M. Becana, I. Iturbe-Ormaetxe, J. M. Chatfield. 1998. Enhanced antioxidant defenses in the oxygen-limiting layers in the cortex of legume root nodules. Plant Physiol. 116:37-43.
Matamoros, M. A., L. M. Baird, P. R. Escuredo, D. A. Dalton,
F. R. Minchin, I. Iturbe-Ormaetxe, M., C. Rubio, J. F. Moran, A. J. Gordon,
and M. Becana. 1999. Stress-induced legume root nodule senescence: physiological,
biochemical, and structural alterations. Plant Physiol. 121:97-111.
Ross*, E. J. H., S. B. Kramer*, and D. A. Dalton. 1999.
Effectiveness of ascorbate and ascorbate peroxidase in promoting nitrogen
fixation in model systems. Phytochemistry 52:1203-1210.
Bashor*, C. J.
and D. A. Dalton. 1999. Effects of exogenous application and stem infusion
of ascorbate on soybean (Glycine max) root nodules. New
Phytol. 142:19-26.
Becana, M. D. A. Dalton, J. F. Moran, I. Iturbe-Ormaetxe, M. A. Matamoros and
M. C. Rubio. 2000. Reactive oxygen species and antioxidants in legume root
nodules Physiol. Plant. 109:372-381.
Iturbe-Ormaetxe, I., M. A. Matamoros, M. C. Rubio, D. A. Dalton, and M. Becana.
2001. The antioxidants of legume nodule mitochondria. Molecular Plant Microbe
Interactions 14:1189-1196.
Ross, S. W., D. A. Dalton, S. Kramer*, and B. L. Christensen. 2001. Physiological
(antioxidant) responses of estuarine fishes to variability in dissolved oxygen.
Comp. Biochem. Physiol. Part C 130:289-303.
Brown*, P. J. and D. A. Dalton. 2002. In situ physiological monitoring of Lobaria
oregana transplants in an old-growth forest canopy. Northwest Science 76:230-239.
Matamomros, M.A., D. A. Dalton, M. R. Clemente, M. C. Rubio,J. Ramos, and M.
Becana. 2003. Biochemistry and molecular biology of antioxidants in the rhizobia-legume
symbiosis. Plant Physiol. 133:1-11.
Dalton, D.A. 2003. Special roles of micronutrients in symbiotic nitrogen fixation.
In: Encyclopedia of Plant & Crop Science, Ed. R. M. Goodman. Marcel Dekker,
New York. [in press].
Dalton, D.A., Sasha Kramer*, Nico
Azios*, Suzanne Fusaro*, Elizabeth
Cahill*,
and Christina Kennedy. 2003. Endophytic nitrogen fixation
in dune grasses (Ammophila
arenaria and Elymus mollis) from Oregon. FEMS
Microbiol. Ecol. 49:469-479.
Some clickable links:
My
nitrogen fixation page
Lab crew Student at work Typical day at the office
Return to Biology Dept. Home Page
Maintained by the Reed College Biology Department
Last Modified 8/20/07 Questions/Comments to David.Dalton@directory.reed.edu