Oxidative stress affects alpha-tocopherol content in soybean embryonic axes upon imbibition and following germination

The content of alpha-tocopherol (alpha-T) in isolated soybean (Glycine max, var Hood) embryonic axes was measured upon germination. Dry, high-vigor axes contained 1.2 +/- 0.1, nmol/axis and after an increase during the initial 6 h of imbibition, there was a decline to 1.0 +/- 0.1 nmol/axis at 24 h of incubation. Incubation in the presence of the redox-cycling agent paraquat (4 mM) for 24 h increased the alpha-T content to 1.9 +/- 0.2 nmol/axis. When the incubation medium was supplemented with 500 micromolars Fe-EDTA over 24 h, the content of aT increased to 1.8 +/- 0.1 nmol/axis. Isolated axes from soybean seeds stored for 56 months contained 6.5 +/- 0.3 nmol of alpha-T/axis after 24 h of imbibition as compared to 1.0 +/- 0.1 nmol of alpha-T/axis in axes from soybean seeds stored for 8 months. In all of these experimental situations, oxidant production as assessed in vivo by a fluorometric assay was increased by 4 mM paraquat (8-fold), 500 micromolars iron (2-fold), and 56 months of storage (4-fold) after 24 h of imbibition. The data presented here suggest that the cellular content of alpha-T is physiologically adjusted as a response to conditions of oxidative stress.