Professor David Day
DipTeach BSc PhD(Adel)
Position: Head of Department, Biochemistry
Affiliation: University of Western Australia, School of School of Biomedical and Chemical Sciences, Biochemistry Department
School of Biomedical & Chemical Sciences
Faculty of Life & Physical Sciences
University of Western Australia
Phone: +61 (08) 9380 3324
Symbiotic Nitrogen Fixation
Symbiotic nitrogen fixation occurs in specialised root outgrowths, called nodules, which form when legume roots are infected by soil bacteria from the genera Rhizobia and Bradyrhizobia. The aim of my research in this area is to elucidate metabolic pathways, especially membrane transport pathways, associated with nitrogen fixation in infected cells of soybean nodules, and to study their regulation. A focus is the peribacteroid membrane (PBM) which surrounds the bacteroid and controls the exchange of metabolites and other compounds between the partners. Our approach involves enzymology, isolation of membranes, electrophysiology of transporters and isolation of genes encoding transporters. To date we have identified transporters for ammonium, malate, and metals, and have characterised an ATPase on the membrane.
Molecular Biology of Plant Mitochondria
Plant mitochondria, like their animal counterparts, are primarily concerned with ATP synthesis driven by organic acid oxidation. However, plant mitochondria also have some unique features which reflect their participation in autotrophic metabolism. I am interested in the interaction between mitochondrion and nucleus during mitochondrial biogenesis in plants and my research group is investigating the synthesis and assembly of enzyme complexes in the respiratory chain. We are also investigating the regulation of electron transport activity, attempting to place respiration in the context of overall plant carbon and nitrogen metabolism. Our focus here is on the dual terminal oxidases of the plant respiratory chain: cytochrome oxidase and the alternative oxidase (AOX). The latter is thought to be an antioxidant stress protein whose action prevents the formation of reactive oxygen intermediates from the respiratory chain. We have identified feedforward regulatory mechanisms which govern the activity of AOX and are now investigating how these mechanisms relate to function in the plant.
In addition to the above mentioned fundamental studies, we are also involved in a more strategic project involving generation of transgenic plants with altered levels of respiratory proteins.
- Tyerman, S.D., Whitehead, L. & Day, D.A. 1995 A channel permeable to ammonium on the symbiotic interface between a legume and nitrogen-fixing bacteroids. Nature. 378, 629-632.
- Whitehead, L. and Day, D.A. 1997. The peribacteroid membrane of legume nodules. Physiologia Plantarum 100: 30-44.
- Udvardi, M.K. and Day, D.A. 1997. Metabolite transport across symbiotic membranes of legume nodules. Annu Rev Plant Physiol Plant Molec Biol. 48: 493-523.
- Millar, A.H. and Day, D.A. 1997. An alternative solution to a radical problem. 1997. Trends in Plant Science 2: 289-290.
- A.H. Millar, O.K. Atkin, R.I. Menz, B. Henry, G. Farquhar and D. A. Day. 1998. An analysis of respiratory chain regulation in roots of soybean seedlings. Plant Physiology 117: 1083-1093.
- Djajanegara, I., Holtzapffel, R.C., Finnegan, P.M., Hoefnagel, M. H. N., Berthold, D.A., Wiskich, J.T. and Day, D.A. (999. A Single Amino Acid Change in the Plant Alternative Oxidase Alters the Specificity of Organic Acid Activation. FEBS Letters 454: 220-224.