EFFECT OF OXIDATIVE STRESS DURING IMBIBITION OF SOYBEAN EMBRYONIC AXES

Both respiration and O-2(.-) generation by soybean embryonic axes show ed a sharp increase upon germination, leading to a significant increas e in the steady-state concentration of O-2(.-) and H2O2 after 6 h of i mbibition. An assay was developed to assess in vivo generation of reac tive oxygen species, based upon DCFH-DA oxidation. Fluorescence of the external medium was dependent on reaction time and axes number and wa s inhibited by catalase. alpha-Tocopherol content declined significant ly after 24 h of incubation, as compared to the content at the onset o f germination. Incubation in the presence of redox cycling agent paraq uat (4 mM) for 24 h increased alpha-tocopherol content to 1.9 +/- 0.2 nmol per axis from 1.0 +/- 0.1 nmol per axis in the absence of paraqua t. Supplementation of the incubation medium with 500 mu M Fe-EDTA incr eased alpha-tocopherol content to 1.8 +/- 0.1 nmol/axis and DCFH-DA ox idation by two-fold. The data presented here showed that active metabo lism at the onset of germination increased steady-state concentration of oxygen active species and suggest that cellular content of alpha-to copherol is physiologically adjusted as a response to conditions of ox idative stress.