PARENT SESSION

Symposium S1B Photooxidative stress, photoinhibition
Monday August 30th, 2004 10:20 AM-12:20 PM Room 210A
Chair: Christine Foyer
Co-Chair: Klaus Apel

The function of chloroplast peroxiredoxins in peroxide detoxification and redox signalling in context of photosynthesis. Karl-Josef Dietz^*,1, Petra Lamkemeyer¹, Wen-Xue Li¹, Iris Finkemeier¹, Tina Stork¹, Elke Ströher¹, Margarete Baier¹, ¹ Biochemistry and Physiology of Plants, University of Bielefeld, Bielefeld, Germany

ABSTRACT- Chloroplasts maintain an intricate system of defence and repair mechanisms under control of diverse regulatory circuits, to counteract progression of photoinhibition. From a rather general view, photoinhibition is defined as a state of decreasing photosynthetic efficiency in response to excess light. One particular process within the network is the detoxification of reactive oxygen species (ROS) produced in photosynthetic electron transport. Redox sensing and redox dependent signalling are central regulatory elements in the process of optimising the performance of photosynthesis and minimizing ROS production. Recently, peroxiredoxins (Prx) were identified in plants. They represent a group of thiol enzymes that detoxify diverse peroxide substrates using a conserved catalytic cysteinyl group (Dietz 2003, Annu Rev Plant Biol 54). From the ten genes identified in the Arabidopsis genome, four are targeted to the chloroplast, namely 2-Cys Prx A and B, Prx Q and Prx IIE. Experimental evidence from in vitro studies and mutant plants has shown that the former three can participate in the water-water cycle of detoxification of hydrogen peroxide. In addition, they attach to the thylakoid membrane where they may modulate photosynthetic activity as indicated in 77 K fluorescence analyses. Reversible thylakoid association of the 2-Cys Prx depends on redox dependent conformational changes, triggering aggregation of dimers to donut-like decamers that associate with the thylakoid. A complex expressional control implicating redox and ABA signals is superimposed on the activity and distribution regulation.

KEY WORDS: redox signalling, peroxiredoxin, photoinhibition, regulation