The tripeptide glutathione (GSH, y-glutamyl-cysteinyl-glycine) is the main low molecular weight thiol in most plant tissues. Due to the particular properties of the molecule it plays multiple roles in cellular metabolism. It is a central compound in sulphur metabolism and is considered the main transport form of reduced sulphur (Rennenberg and Lamoureux 1990). It links the sulphur reduction pathways to the protein synthesis and functions as a buffer for reduced sulphur. Glutathione also plays an important role in the scavenging of toxic reactive oxygen species (ROS). The activation of dioxygen (02) is an important aspect of the cell metabolism (Elstner 1982). The active oxygen species formed in the course of oxygen activation processes are highly reactive and difficult to keep under control. The action of ROS in cells is called oxidative stress. Oxidative stress is an inescapable feature of life in an oxygen atmosphere and ROS are involved in nearly all effects of environmental stresses on plants (Elstner and Osswald 1994, De Kok and Stulen 1993). The capacity of the glutathione redox system to detoxify dangerous ROS is potentially dependent on the pool size of total GSH, on the redox ratio GSH/GSSG (GSSG = oxidized glutathione), and on the activity of the regenerating enzyme system, the NADPH-dependent glutathione reductase. Elevated levels of GSH appear to be correlated to active plant responses to environmental stress and responses of GSH synthesis, GSH redox status, and GSH related enzyme activities have been found repeatedly in plants under stress (Alscher 1989).

D. Grill etal. (eds.), Significance of Glutathione to Plant Adaptation to the Environment, 101-122. © 2001 KluwerAcademic Publishers. Printed in the Netherlands.

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