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

• Main Authors: Taoufik Amari, Aymen Souid, Rim Ghabriche, Mauro Porrini, Stanley Lutts, Gian Attilio Sacchi, Chedly Abdelly, Tahar Ghnaya
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Plants
• Subjects: antioxidant systems; glycophyte; halophyte; nickel stress; phytoremediation
• Online Access: https://www.mdpi.com/2223-7747/9/3/312

The implication of enzymatic and non-enzymatic antioxidative systems in response to Ni was evaluated in the halophyte <i>Mesembryanthemum crystallinum</i> in comparison with the metal tolerant glycophyte species <i>Brassica juncea</i>. Seedlings of both species were hydroponically subjected during 21 days to 0, 25, 50, and 100 &#181;M NiCl₂. Growth parameters showed that the halophyte <i>M. crystallinum</i> was more tolerant to Ni than <i>B. juncea</i>. Malondialdehyde (MDA) content increased to a higher extent in <i>B. juncea</i> than in <i>M. crystallinum</i>. Antioxidant enzymesactivities were differently affected by Ni in both species. Nickel increased shoot superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in <i>B. juncea</i>, whereas these activities were reduced in <i>M. crystallinum</i> 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 <i>B. juncea.</i> Based on the oxidative balance, our findings confirm the higher tolerance of the halophyte <i>M. crystallinum</i> to Ni-induced oxidative stress comparatively to <i>B. juncea.</i> We suggest that <i>M. crystallinum</i> is able to overcome the produced ROS using the non-enzymatic system, while Ni-induced oxidative stress was more acute in <i>B. juncea</i>, leading this species to mainly use the enzymatic system to protect against reactive oxygen species.