This project envisages identifying components of the signal transduction cascades during oxidative stress in plants by means of an integrated immunological and proteomic approach. During its development a plant is continuously exposed to various kinds of stress. Its ability to react to these changes in a fast and appropriate manner is essential for its survival. Very often, changes in hormone homeostasis play an important role. Our knowledge regarding the role of plant growth regulators such abscisic acid (ABA), ethylene, jasmonic acid (JA) and salicylic acid (SA) as important signal molecules in stress responses is already substantial. Stress induced auxin and cytokinin action has been described in a restricted set of stress phenomena. Various studies point to oxidative stress as a central component in many cellular responses (Desikan et al., 2001; Neill et al., 2002). Oxidative stress results from an imbalance in the production and metabolism of reactive oxygen species (ROS). ROS are produced as a response to exposure to biotic and abiotic stress and act as a signal that triggers a variety of molecular, biochemical and physiological events. Nitrogen monoxide (NO) is very often an important component in the underlying signal transduction cascades. NO, a gaseous free radical, can interact with ROS in a number of ways and as such influences the response to biotic and abiotic stress factors (Delledonne et al., 1998; Neill et al., 2002; Neill et al., 2003). As is the case in animal models, cyclic GMP and cyclic ADPR are put forward as signal molecules in the plant NO signal transduction system. Cyclic GMP is produced in plants as a response to NO application (Pfeiffer et al., 1994) and in turn cADPR synthesis is thought to be induced by cGMP. Both have been shown to mimic certain functions of NO (Durner et al., 1998), and a specific inhibitor of guanylyl cyclase (ODQ) inhibits Arabidopsis thaliana NO-induced cell death. A membrane permeable cGMP-analog, 8-Br-cGMP, eliminates this inhibitory effect (Clarke et al., 2000). In animal systems, stress induced cADPR synthesis is activated via cGMP-dependent protein kinase. Until now, the existence of such a protein in higher plants has not been reported yet. The recent isolation of the gene for a putative cyclic nucleotide dependent protein kinase in our lab is a convincing candidate for this function. In its promoter region a considerable number of stress-regulated elements are found, such as the ABA-response element (ABRE), the "heat shock"-response element, the ABRE related "GC-repeat" (Litis et al., 1992) and the cold and water stress regulated dehydration (DRE)/"C-repeat"-response elements (Baker et al., 1994). The additional presence of a salicylic acid regulated
promoter element (TCA), a wound induced response element, (WUN) (Pastuglia et al., 1997), and of the "TC-rich repeat", a stress and defence induced response element (Klotz en Lagrimini 1996), strengthens our proposition for a stress related function of this putative cyclic nucleotide dependent protein kinase.