The biochemistry of plant stress and disease oxygen activation as a basic principle

Green plants can adapt to a wide variety of unfavorable conditions such as drought, flooding, temperature changes, light variations, infections, air pollution, and soil contamination. Dependent on these impacts, visible or measurable changes indicate the deviation from normal metabolic conditions. Most symptoms are connected with altered oxygen metabolism chemically characterized as a transition from heterolytic (two electron abstraction or donation) to increased homolytic (one electron transition) processes. Homolytic reactions generate reactive oxygen species, some of which are free radicals. Therefore, these reactions have to be counteracted by a parallel increase of antioxidatively working compounds or processes. Continuation of stress impacts cause the loss of control and initiation of "chaotic" radical processes, where cellular decompartmentalizations induce lytic and necrotic reactions. This sequence of events is species-, organ-, and stress-specific.