ALPHA-TOCOPHEROL-DEPENDENT SALT TOLERANCE IS MORE RELATED WITH AUXIN SYNTHESIS RATHER THAN ENHANCEMENT ANTIOXIDANT DEFENSE IN SOYBEAN ROOTS

In this paper, we describe the alleviated effects of alpha-tocopherol (alpha-T) on oxidative damage and its possible role as a signal transmitter in plants during salt stress. The results show that exogenously applied alpha-T under salt stress increased root length and weight, but reduced hydrogen peroxide (H2O2), superoxide anion radical (O-2 center dot(-)) and malondialdehyde (MDA) content in soybean roots. The proline content was reduced by alpha-T treatment. Interestingly, endogenous auxin (IAA) level was significantly increased after alpha-T application as compared to salt stress alone. Moreover, alpha-T reduced significantly superoxide dismutase (SOD) enzyme and isoenzyme activity but upregulated peroxidase (POX) 2, 3 and glutathione-stransferase (GST) 1, 3 isoenzyme expression. However, ascorbate peroxidase (APX) enzyme activity was not affected at all. Consequently, the results show that alpha-T serves as a signal molecule under salinity from leaves to roots by increasing remarkably endogenous IAA levels and increasing partially antioxidant activity in roots.