Aims Oxidative stress is one of the most important mechanisms in a plant's reaction to the effects of different stressors; however, its role in plants' resistance is still poorly understood. The objective of this study is to evaluate an influence of oxidative stress induced by stress factors of different origin—ozone, ultraviolet (UV)-B radiation, drought, cadmium (Cd) and copper (Cu), to growth of spring barley and to check the hypothesis, that intensification of oxidative stress is the main factor of growth depression induced by strong treatments of different stressors; meanwhile, mitigation of oxidative stress determines eustress-induced growth stimulation.
Methods A pot experiment was carried out in phytotron chambers with a controlled environment. Spring barley (Hordeum vulgare L.) plants were exposed to different doses of investigated environmental stress factors (O 3, UV-B radiation, drought, Cd and Cu), and their effects on shoots growth, accumulation of superoxide (O 2 .?), intensification of lipid peroxidation and antioxidative protection (superoxide dismutase, glutathione reductase and catalase activities and concentration of carotenoids) were measured. Analysis of variance (ANOVA) with classical eta-squared (η 2) values was used to evaluate and to compare the contribution of non-specific oxidative stress and stressor-specific mechanisms on plants growth.
Important findings Low doses of most stressors stimulated antioxidative protection and growth of barley shoots, reduced the concentration of O 2 .? and/or intensity of lipid peroxidation. Whereas an impairment of growth and intensification of oxidative stress as well as a reduction in concentration of carotenoids and further increase in activity of antioxidative enzymes were noticed when the intensity of the stressors was increased. In the cases of ozone and UV-B stress, the effects of oxidative stress on plant growth was mitigated by strong antioxidative protection—highly increased catalase (CAT) and superoxide dismutase (SOD) activities, respectively. In the cases of drought and Cu, relatively strong oxidative stress was the major cause of plant growth depression. Additionally, mitigation of oxidative stress due to increased SOD activity was likely to be one of the main causes of growth stimulation induced by low doses of UV-B, Cd and Cu stress. Possible reasons for O 3 -induced growth stimulation were increased CAT activity and concentration of carotenoids. Generalizing the effects of different stressors, the contribution of non-specific oxidative stress on plant growth was stronger compared with stressor-specific action mechanisms: oxidative stress determined 42% of the changes in plants' dry biomass, whereas the contribution of stressor-specific mechanisms accounted for 35% of variability in barley growth.