Until recent years the production of reactive oxygen species (ROS) was generally considered to be a harmful process and a generator of oxidative stress. But more recently this concept has been re-evaluated and the term "oxidative signaling" was coined (Foyer and Noctor, 2005). This means that ROS generation is also an important component of the signaling network of plants. Results obtained during the last decade have highlighted that ROS are key regulators of plant metabolism, morphology and development which are also used by plants to respond to environmental challenges. The role of ROS as signals for gene expression has been established, and ROS also modulate the activity of key signaling compounds such as MAP kinases. The volume of research into the roles of ROS in plants is currently growing and the purpose of this book is to present recent advances in this field. The constitutive chapters are arranged around four main topics:

The generation of ROS and their network signaling, including the retrograde signaling from the chloroplast to the nucleus and the cross-talk with hormone signaling

-The signaling role of ROS produced in some sub-cellular compartments

-The role of ROS in plant growth, development, functioning and stress acclimation

-Their role in biotic and abiotic interactions

Zusammenfassung
Oxygen (O ) appeared in significant amounts in the Earth's atmosphere over 2. 2 2 billion years ago, largely due to the evolution of photosynthesis by cyanobacteria (Halliwell 2006). The O molecule is a free radical, as it has two impaired electrons 2 that have the same spin quantum number. This spin restriction makes O prefer to 2 accept its electrons one at a time, leading to the generation of the so-called reactive oxygen species (ROS). The chemical nature of these species dictates that they can create damage in cells. This has contributed to the creation of the oxidative stress concept; in this view, ROS are unavoidable toxic products of O metabolism and 2 aerobic organisms have evolved antioxidant defences to protect against this tox- ity (Halliwell 1981; Fridovich 1998). Indeed, even in present-day plants, which are full of antioxidants, much of the protein synthetic activity of chloroplasts is used to replace oxidatively damaged D1 and other proteins (Halliwell 2006). Yet, the use of the oxidative stress term implies that ROS exert their effects through indiscriminate widespread inactivation of cellular functions. In this context, ROS must not be able to react with lipids, proteins or nucleic acids in order to avoid any damage to vital cellular components. However, genetic evidence has suggested that, in planta, purely physicoche- cal damage may be more limited than previously thought (Foyer and Noctor 2005).

Inhalt
Reactive Oxygen-Generating NADPH Oxidases in Plants.- Integration of ROS and Hormone Signaling.- Reactive Oxygen Species in Growth and Development.- ROS Signalling in Stomata.- Reactive Oxygen Species in Plant Cell Walls.- Peroxisomes as a Cellular Source of ROS Signal Molecules.- Reactive Oxygen Species in PlantPathogen Interactions.- ROS in the Legume-Rhizobium Symbiosis.- Hydrogen Peroxide-Responsive Genes in Stress Acclimation and Cell Death.- The ROS Signaling Network of Cells.- Reactive Oxygen Species and Signaling in Cadmium Toxicity.- Reactive Oxygen Species in Ozone Toxicity.- ROS and Plant Membrane Rafts.- ROS in Retrograde Signalling from the Chloroplast to the Nucleus.