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Published on April 10, 2009; 10.1104/pp.109.135566

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Received January 13, 2009
Accepted April 6, 2009

Arabidopsis chloroplastic glutathione peroxidases play a role in cross-talk between photooxidative stress and immune responses

Christine C.C. Chang , Ireneusz Slesak , Lucia Jorda , Alexey Sotnikov , Michael Melzer , Zbigniew Miszalski , Philip M. Mullineaux , Jane E. Parker , Barbara Karpinska *, and Stanislaw Karpinski *

Department of Botany, Stockholm University, Frescati, 10691 Stockholm, Sweden; Institute of Plant Physiology, Polish Academy of Sciences, Niezapominajek 21, 30-239 Krakow, Poland; Department of Plant-Microbe Interactions, Max-Planck Institute for Plant Breeding Research, Carl-von-Linne Weg 10, D-50829 Cologne, Germany; Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany; Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom; Department of Plants Genetics, Breeding and Biotechnology, University of Life Sciences, Nowoursynowska Street 159, 02-776 Warszawa, Poland

* Corresponding author; email: Stanislaw_Karpinski{at}sggw.pl.

Glutathione peroxidases (GPXs, EC: 1.11.1.9) are key enzymes of the antioxidant network in plants and animals. In order to investigate the role of antioxidant systems in plant chloroplasts we generated Arabidopsis transgenic lines that are depleted specifically in chloroplastic (cp) forms of GPX1 and GPX7. We show that reduced cpGPX expression, either in transgenic lines with lower total cpGPX expression (GPX1 and GPX7) or in a gpx7 insertion mutant, leads to compromised photooxidative stress tolerance but increased basal resistance to virulent bacteria. Depletion of both GPX1 and GPX7 expression also caused alterations in leaf cell and chloroplast morphology. Leaf tissues were characterized by shorter and more rounded palisade cells, irregular spongy mesophyll cells and larger intercellular air spaces compared to wild type. Chloroplasts had larger and more abundant starch grains than in wild type and gpx7 mutant plants. Constitutively reduced cpGPX expression also led to higher foliar ascorbic acid, glutathione and salicylic acid levels in plants exposed to higher light intensities. Our results suggest partially overlapping functions of GPX1 and GPX7. The data further point to specific changes in the chloroplast ascorbate-glutathione cycle due to reduced cpGPX expression, initiating reactive oxygen species and salicylic acid pathways that impact on leaf developmental, light acclimation, basal defence and cell death programs. Thus, chloroplastic GPXs regulate cellular photooxidative tolerance and immune response.






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