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Edgar P. Spalding
Professor of Botany
Ph.D. (1990) Pennsylvania State University
Office: B135 Birge
Hall
Phone: 608-265-5294
Email: spalding@wisc.edu
Transport of ions including auxin; photosensory transduction; development of morphometric tools
Current Projects
Cryptochrome
MDR1, auxin and lateral roots
MDR1, auxin and gravitropism
Ionotropic glutamate receptors
In addition to powering plants through photosynthesis, light exerts profound effects on their growth and development by acting as a signal. This latter photomorphogenic role of light is mediated by photoreceptors that are coupled to developmental responses by serial molecular events known as transduction chains. We are studying one photomorphogenic response in particular detail, the light-induced inhibition of stem elongation in seedlings. Using the patch clamp technique, we have learned that rapid activation of chloride ion channels is an important event in the transduction chain that links cryptochrome blue-light receptors to the control of cell elongation. We are also studying how phytochrome photoreceptors transduce red light into growth inhibition, and how the red and blue photosensory systems interact. In order to learn when a particular receptor contributes to a response, we developed electronic techniques for measuring the growth rate of tiny Arabidopsis seedlings and used these techniques to study how mutants lacking specific photoreceptors respond to light. This temporal information helped us focus DNA microarray experiments on the specific question of what genes act downstream of the cry1 photoreceptor to control growth in blue light. Sometimes our investigations turn in unexpected directions. For example, our efforts to clone the gene encoding the light-activated chloride channel resulted in the discovery that multidrug-resistance-like ABC transporters are required for distributing auxin throughout the plant.
We also study ion channels important to plant mineral nutrition using electrophysiology and genetics. These investigations, too, have turned in unexpected but interesting directions. While studying mutants lacking a potassium uptake channel (AKT1) in their roots, we discovered that the neurotransmitter glutamate triggers a large, fast spike in intracellular calcium in plant cells much like it does in our brains. We are presently studying the family of Arabidopsis ionotropic glutamate receptors using genetics and electrophysiology. A lot of exciting things happen at the membranes of plant cells.
In all of our projects, we have encountered the need to measure the effects of mutations (phenotypes) with high precision over time, as the phenotype develops. Electrophysiological phenotypes pose no special problems because techniques exist for measuring currents and voltages with high resolution. But if the phenotype is, for example, a difference in growth rate of a stem that is only 3 mm tall, off-the-shelf techniques do not exist. So, we are developing (engineering may be a better word) new techniques for measuring growth and development phenotypes. Our approach is to create software that can extract information about growth rates and shape parameters such as curvature from sequential electronic images of seedlings acquired as they develop. In short, we are developing morphometric tools for the purpose of quantifying the effects of mutations on plant development. Our goal is to create a combination of hardware and software that will enable the high-throughput phenotyping of the large Arabidopsis mutant collections.
Selected Publications (full publication list here)
Stephens NR, Qi Z, Spalding EP (2008) Glutamate receptor subtypes evidenced by differences in desensitization and dependence on the GLR3.3 and GLR3.4 genes. Plant Physiology 146: 529-538
Wu G, Spalding EP (2007) Separate functions for nuclear and cytoplasmic cryptochrome 1 during photomorphogenesis of Arabidopsis seedlings. Proceedings of the National Academy of Sciences USA 104: 18813-18818
Miller ND, Parks BM, Spalding EP (2007) Computer-vision analysis of seedling responses to light and gravity. The Plant Journal 52: 374-381
Wu G, Lewis DR, Spalding EP (2007) Mutations in Arabidopsis Multidrug Resistance-like ABC transporters separate the roles of acropetal and basipetal auxin transport in lateral root development. The Plant Cell 19: 1826-1837
Lewis DR, Miller ND, Splitt BL, Wu G, Spalding EP (2007) Separating the roles of acropetal and basipetal auxin transport on gravitropism with mutations in two Arabidopsis Multidrug Resistance-like ABC transporter genes. The Plant Cell 19: 1838-1850
Spalding EP (2006) The Contributions of Anthony B. Bleecker to Ethylene Signaling and Beyond. The Plant Cell 18: 3347-3349
Qi Z, Stephens NR, Spalding EP (2006) Calcium entry mediated by GLR3.3, an Arabidopsis glutamate receptor with a broad agonist profile. Plant Physiology 142: 963-971
Qi Z, Spalding EP (2004) Protection of plasma membrane K+ transport by the salt overly sensitive Na+-H+ antiporter during salinity stress. Plant Physiology 136: 2548-2555
Folta KM, Pontin M, Karlin-Neumann G, Bottini R, Spalding EP (2003) Genomic and physiological studies demonstrate roles for auxin and gibberellin in the early phase of cryptochrome1 action in blue light. The Plant Journal 36: 203-214
Noh B, Bandyopadhyay A, Peer WA, Spalding EP, Murphy AS (2003) Enhanced gravi- and phototropism in plant mdr mutants mislocalizing the auxin efflux protein PIN1. Nature 423: 999-1002
Dennison KL, Robertson WR, Lewis BD, Hirsch RE, Sussman MR, Spalding EP (2001) Functions of AKT1 and AKT2 potassium channels determined by studies of single and double mutants of Arabidopsis. Plant Physiology 127: 1012-1019
Folta KM, Spalding EP (2001) Unexpected roles for cryptochrome 2 and phototropin revealed by high-resolution analysis of blue-light-mediated hypocotyl growth inhibition. The Plant Journal 26: 471-478
Dennison KL, Spalding EP (2000) Glutamate-gated calcium fluxes in Arabidopsis. Plant Physiology 124: 1511-1514
Spalding EP, Hirsch RE, Lewis DR, Qi Z, Sussman MR, Lewis BD (1999) Potassium uptake supporting plant growth in the absence of AKT1 channel activity: inhibition by ammonium and stimulation by sodium. Journal of General Physiology 113: 909-918
Parks BM, Spalding EP (1999) Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis. Proceedings of the National Academy of Sciences USA 96: 14142-14146
Hirsch RE, Lewis BD, Spalding EP, Sussman MR (1998) A role for the AKT1 potassium channel in plant nutrition. Science 280: 918-921
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Department of Botany
Last updated: 17 December 2007