Why Does the Halophyte Mesembryanthemum crystallinum Better Tolerate Ni Toxicity than Brassica juncea : Implication of Antioxidant Defense Systems

The implication of enzymatic and non-enzymatic antioxidative systems in response to Ni was evaluated in the halophyte in comparison with the metal tolerant glycophyte species . Seedlings of both species were hydroponically subjected during 21 days to 0, 25, 50, and 100 µM NiCl . Growth parameters showed that the halophyte was more tolerant to Ni than . Malondialdehyde (MDA) content increased to a higher extent in than in . Antioxidant enzymesactivities were differently affected by Ni in both species. Nickel increased shoot superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in , whereas these activities were reduced in when exposed to metal stress. The root SOD, APX and guaiacol peroxidase (GPX) activities increased upon Ni treatments for both species. The content of non-enzymatic antioxidative molecules such as glutathione, non-protein thiols and proline increased in Ni-treated plants, except for GSH content in the shoot of Based on the oxidative balance, our findings confirm the higher tolerance of the halophyte to Ni-induced oxidative stress comparatively to We suggest that is able to overcome the produced ROS using the non-enzymatic system, while Ni-induced oxidative stress was more acute in , leading this species to mainly use the enzymatic system to protect against reactive oxygen species.