Oxidative stress is the process whereby the production of reactive oxygen intermediates (ROIs), which are inevitable by-products of aerobic metabolism, exceed the capacity of the scavenging and antioxidant systems to remove them, resulting in oxidative damage to biological macromolecules. It has been recognised that the effects of a considerable number of environmental stresses can be explained in terms of increased oxidative stress levels. Considerable evidence has now also emerged suggesting that ROIs do not simply act as agents of damage. It has been strongly suggested that ROIs and redox active components such as glutathione, ascorbate and plastoquinone play important roles in initiating defence mechanisms in plants. Low levels of ROIs, which a cell may be able to withstand without major irreversible damage, may serve as messengers that ultimately alter gene expression. The key regulators in this process are the transcription factors, which remain largely unidentified, in the plant system. Understanding (and subsequently enhancing) the tolerance of plants to oxidative stress holds out the prospect of increasing their tolerance of a wide range of environmental stresses. Our focus has been to understand the biochemistry and regulation of enzymes such as superoxide dismutase (SOD), ascorbate reductase (APX) and glutathione reductase (GR).
In addition, the roles of glutathione, ascorbate and plastoquinone on cellular redox regulation is of special interest. The identification of new regulatory genes will be a future goal. Our finding that extracellular forms of superoxide dismutase exist has received a great deal of attention in recent years. Evaluation of the biological functions of these forms using transgenic Populus and Arabidopsis is ongoing. One possible role for the extracellular SODs might be to produce hydrogen peroxide for various biological processes such as lignification. To further explore the function of these forms the Zinnia mesophyll differentiating system is being used in our lab.
MYB-transcription factors
The MYB proteins represent the largest regulatory gene family currently known in plants. The structural element common to all known MYB proteins is the DNA-binding domain, the signature motif of transcription factor families. Although the activity of only a few of these proteins is known, they appear to have distinct functions, such as the control of secondary metabolism, cellular morphogenesis and response to growth factors. Theyprobably also have overlapping functions, as seen in the vertebrate MYB proteins (which are involved in both cell survival and cell death). Also, there are indications that MYBs may be regulated by redox status. In ongoing projects we have identified MYBs from Populus that have putative functions in the regulation of phenylpropanoid biosynthesis and thus also in the lignification of the cell wall. The characterisation and functional analysis of these genes are in process.
Selected publications:
Streller, S. & Wingsle, G . () Pinus sylvestris L.contain extracellular CuZn superoxide dismutase. Planta 192:195-201.
Wingsle, G. & Karpinski, S. () Differential redox regulation by glutathione of glutathione reductase and CuZn-superoxide dismutase gene expression in Pinus sylvestris (L.) needles. Planta .198:151-157.
Wingsle, G. & Moritz, T. () Analysis of ascorbate and dehydroascorbate in plant extracts by high-resolution selected ion monitoring gas chromatography mass spectrometry. J Chromatography 782:95-103.
Karpinski, S., Karpinska, B., Reynolds. H., Wingsle, G. Creissen, G., & Mullineaux, P.M. . Systemic signaling and acclimation in response to excess excitation energy in Arabidopsis. Science. 284:654-657.
Schinkel, H., Streller, S. & Wingsle, G. () Multiple forms of extracellular superoxide dismutase in needles, stem tissues and seeds of Scots pine. J. Exp. Bot. 49:931-936.
Wingsle, G. , Karpinski, S. & Hällgren, J.-E. () Low temperature, high light stress and antioxidant defence mechanisms in higher. Phyton 39:253-268.
