OXIDATIVE AND GROWTH-PROCESSES IN ROOTS AND LEAVES OF HIGHER-PLANTS AT DIFFERENT OXYGEN AVAILABILITY IN SOIL

The activity of superoxide dismutase, the level of malonic dialdehyde, and growth processes in roots and leaves of Zea mays L. and Pisum sat ivum L. were measured at various levels of oxygen availability in soil . On lowering the rate of oxygen diffusion in soil, similar changes we re observed in systems preventing oxidative destruction in root and le af cells, even though the heterotrophic root cells were directly affec ted by the stress factor and the autotrophic leaf cells remained under natural aeration conditions. These changes were coupled to a varying degree with main metabolic processes reflected by growth rate, product ion of biomass and some of its constituents (protein, chlorophyll, car otenoids), and stomatal aperture closely related to the photosynthetic rate. Superoxide dismutase, an enzyme eliminating superoxide anion ra dicals, changed its activity according to a phasic pattern, as the oxy gen diffusion rate decreased progressively and the stress-load dose be came higher; the enzyme activity changes indicated the main stages of the developing hypoxic stress. Each phase comprised several steps that arose from shifting the dynamic equilibrium between the antioxidative activity and the lipid peroxidation under developing stress. Duration and manifestation of each phase in the kinetics of superoxide dismuta se activity and free radical oxidation depended on individual plant re sistance to hypoxia. It is concluded that oxygen deficiency in roots g ives rise to a generalized adaptive response in all plant organs inclu ding leaves with normal oxygen supply. Depending on the stress-load do se, plants mobilize different mechanisms for protecting themselves fro m the hypoxic stress.