Differential response of antioxidant systems in leaves and roots of barley subjected to anoxia and post-anoxia

Mitochondria and chloroplasts are the primary sources of reactive oxygen species in photosynthetic tissues. Mitochondria play a dual role in oxidative stress, being both ROS producers and integrators of the cell antioxidant defense systems. Anoxia followed by re-exposure to air may create conditions of elevated ROS generation in plants. The reactions of barley leaves and root antioxidant systems after anoxia were investigated. Alternative oxidase and low-mass antioxidants showed different patterns of change in leaves and roots in response to changing oxygen availability. Mitochondria from leaves showed a reduced AOX capacity and AOX protein level during post-anoxia, while the AOX capacity in root mitochondria increased. In leaf tissue, ascorbate and glutathione were immediately oxidized after restoration of aerobiosis due to the enhanced ROS production, whereas in roots ascorbate and glutathione became even more reduced. The capacity of antioxidant systems was not exceeded in either leaf or root tissue after anoxia; no signs of oxidative damage were observed and the respiratory activity of mitochondria was retained. We suggest that the leaf and root cell antioxidant systems react differentially to changes in oxygen concentration. In leaves, low-mass antioxidants play the major role in ROS detoxification, while in roots, increased AOX capacity supports the antioxidant systems, possibly by preventing ROS formation.