[Effect of short-term phenanthrene stress on SOD activities and MDA contents in soybean (Glycine max) seedlings]

Growth of soybean (Glycine max) seedlings, changes of superoxide dismutase (SOD) activities, and malonyldialdehyde (MDA) contents were researched during different concentration phenanthrene stress and following recovery from stress. The results showed that seedling growth was interrupted after 5 d in 200 micrograms.g-1 phenanthrene treatment. However, during the period of recovery, growth was restored, although there was a delay in returning to control levels. The dose-related response of SOD activities were observed in manner of linear for 2 d and of parabola for 5 d and 8 d at 50-200 micrograms.g-1 phenanthrene. SOD activities of seedling were significantly induced by 100 and 200 micrograms.g-1 phenanthrene for 2 d (P < 0.05 and P < 0.01), while declined significantly under phenanthrene stress for 8 d, and was 88% of control at 200 micrograms.g-1 phenanthrene (P < 0.05). When releasing soybean seedlings from phenanthrene stress for 5 d to clear tap water for 2 d or 4 d, their SOD activities at 50 and 100 micrograms.g-1 phenanthrene recovered towards control level, while a significant increase in SOD activities was observed at 200 micrograms.g-1 phenanthrene (P < 0.05). The experiments also revealed that a significant increase of MDA contents in seedlings occurred after 5 d and 8 d in 100 and 200 micrograms.g-1 phenanthrene treatment (P < 0.05 and P < 0.01), which suggested that the membrane systems were damaged by phenanthrene stress. All of the above results showed that SOD activities of soybean seedling might be suitable to be the biomarkers of phenanthrene stress.