Detection of free radicals and reactive oxygen species.

In plants, reactive oxygen species (ROS), also known as active oxygen species (AOS), are associated with normal, physiological processes as well as with responses to adverse conditions. ROS are associated with stress in many ways; as primary elicitors, as products and propagators of oxidative damage, or as signal molecules initiating defense or adaptation. The photosynthetic electron transport is a major site of oxidative stress by visible or ultraviolet light, high or low temperature, pollutants, or herbicides. ROS production can be presumed from detecting oxidatively damaged lipids, proteins, or pigments as well as from the alleviating effects of added antioxidants. On the other hand, measuring ROS by special sensor molecules provides more direct information. This chapter focuses on the application of spin trapping electron paramagnetic resonance (EPR) spectroscopy for detecting ROS; singlet oxygen and oxygen free radicals in thylakoid membrane preparations.