AUTHOR=Hasanuzzaman Mirza , Nahar Kamrun , Gill Sarvajeet S. , Alharby Hesham F. , Razafindrabe Bam H. N. , Fujita Masayuki 

TITLE=Hydrogen Peroxide Pretreatment Mitigates Cadmium-Induced Oxidative Stress in Brassica napus L.: An Intrinsic Study on Antioxidant Defense and Glyoxalase Systems

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00115

DOI=10.3389/fpls.2017.00115

ISSN=1664-462X

ABSTRACT=<p>Cadmium (Cd) is considered as one of the most toxic metals for plant growth and development. In the present study, we investigated the role of externally applied hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) in regulating the antioxidant defense and glyoxalase systems in conferring Cd-induced oxidative stress tolerance in rapeseed (<italic>Brassica napus</italic> L.). Seedlings were pretreated with 50 μM H<sub>2</sub>O<sub>2</sub> for 24 h. These pretreated seedlings as well as non-pretreated seedlings were grown for another 48 h at two concentrations of CdCl<sup>2</sup> (0.5 and 1.0 mM). Both the levels of Cd increased MDA and H<sub>2</sub>O<sub>2</sub> levels and lipoxygenase activity while ascorbate (AsA) declined significantly. However, reduced glutathione (GSH) content showed an increase at 0.5 mM CdCl<sup>2</sup>, but glutathione disulfide (GSSG) increased at any level of Cd with a decrease in GSH/GSSG ratio. The activities of ascorbate peroxidase (APX) and glutathione <italic>S</italic>-transferase (GST) upregulated due to Cd treatment in dose-dependent manners, while glutathione reductase (GR) and glutathione peroxidase (GPX) increased only at 0.5 mM CdCl<sup>2</sup> and decreased at higher dose. The activity of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II) decreased under Cd stress. On the other hand, H<sub>2</sub>O<sub>2</sub> pretreated seedlings, when exposed to Cd, AsA and GSH contents and GSH/GSSG ratio increased noticeably. H<sub>2</sub>O<sub>2</sub> pretreatment increased the activities of APX, MDHAR, DHAR, GR, GST, GPX, and CAT of Cd affected seedlings. Thus enhancement of both the non-enzymatic and enzymatic antioxidants helped to decrease the oxidative damage as indicated by decreased levels of H<sub>2</sub>O<sub>2</sub> and MDA. The seedlings which were pretreated with H<sub>2</sub>O<sub>2</sub> also showed enhanced glyoxalase system. The activities of Gly I, and Gly II and the content of GSH increased significantly due to H<sub>2</sub>O<sub>2</sub> pretreatment in Cd affected seedlings, compared to the Cd-stressed plants without H<sub>2</sub>O<sub>2</sub> pretreatment which were vital for methylglyoxal detoxification. So, the major roles of H<sub>2</sub>O<sub>2</sub> were improvement of antioxidant defense system and glyoxalase system which protected plants from the damage effects of ROS and MG. The mechanism of H<sub>2</sub>O<sub>2</sub> to induce antioxidant defense and glyoxalase system and improving physiology under stress condition is not known clearly which should be elucidated. The signaling roles of H<sub>2</sub>O<sub>2</sub> and its interaction with other signaling molecules, phytohormones or other biomolecules and their roles in stress protection should be explored.</p>