Up-regulation of antioxidant and glyoxalase systems by exogenous glycinebetaine and proline in mung bean confer tolerance to cadmium stress

Abstract

The present study investigates the possible mediatory role of exogenously applied glycinebetaine (betaine) and proline on reactive oxygen species (ROS) and methylglyoxal (MG) detoxification systems in mung bean seedlings subjected to cadmium (Cd) stress (1 mM CdCl2, 48 h). Cadmium stress caused a significant increase in glutathione (GSH) and glutathione disulfide (GSSG) content, while the ascorbate (AsA) content decreased significantly with a sharp increase in hydrogen peroxide (H2O2) and lipid peroxidation level (MDA). Ascorbate peroxidase (APX), glutathione S-transferase (GST), glutathione peroxidase (GPX), and glyoxalase I (Gly I) activities were increased in response to Cd stress, while the activities of catalase (CAT), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and glyoxalase II (Gly II) were sharply decreased. Exogenous application of 5 mM betaine or 5 mM proline resulted in an increase in GSH and AsA content, maintenance of a high GSH/GSSG ratio and increased the activities of APX, DHAR, MDHAR, GR, GST, GPX, CAT, Gly I and Gly II involved in ROS and MG detoxification system as compared to the control and mostly also Cd-stressed plants, with a concomitant decrease in GSSG content, H2O2 and lipid peroxidation level. These findings together with our earlier findings suggest that both betaine and proline provide a protective action against Cd-induced oxidative stress by reducing H2O2 and lipid peroxidation levels and by increasing the antioxidant defense and MG detoxification systems.

Keywords: Antioxidant defense; Cadmium stress; Glycinebetaine; Glyoxalase system; Mung bean; Proline; Reactive oxygen species.

Fig. 1

Reduced ascorbate (AsA) contents in mung bean seedlings induced by proline and betaine under cadmium stress conditions. Cd, Cd+P and Cd+B indicates 1 mM CdCl₂, 1 mM CdCl₂+5 mM proline and 1 mM CdCl₂+5 mM betaine treatments, respectively. Each value is the mean±SE from four independent experiments. Bars with different letters are significantly different at P < 0.05

Fig. 2

Glutathione accumulation in mung bean seedlings induced by proline and betaine under cadmium stress conditions. a: reduced glutathione (GSH), b: oxidized glutathione (GSSG), c: GSH/GSSG ratio. Cd, Cd+P and Cd+B indicates 1 mM CdCl₂, 1 mM CdCl₂+5 mM proline and 1 mM CdCl₂+5 mM betaine treatments, respectively. Each value is the mean±SE from four independent experiments. Bars with different letters are significantly different at P < 0.05

Fig. 3

Activities of APX (a), MDHAR (b), DHAR (c), GR (d), GPX (e), GST (f) and CAT (g) in mung bean seedlings induced by proline and betaine under cadmium stress conditions. Cd, Cd+P and Cd+B indicates 1 mM CdCl₂, 1 mM CdCl₂+5 mM proline and 1 mM CdCl₂+5 mM betaine treatments, respectively. Each value is the mean±SE from four independent experiments. Bars with different letters are significantly different at P < 0.05.

Fig. 4

Activities of Gly I (a) and Gly II (b) in mung bean seedlings induced by proline and betaine under cadmium stress conditions. Cd, Cd+P and Cd+B indicates 1 mM CdCl₂, 1 mM CdCl₂+5 mM proline and 1 mM CdCl₂+5 mM betaine treatments, respectively. Each value is the mean±SE from four independent experiments. Bars with different letters are significantly different at P < 0.05

Fig. 5

Changes in H₂O₂ concentration (a) and lipid peroxidation (represented by MDA) (b) level in mung bean seedlings induced by proline and betaine under cadmium stress conditions. Cd, Cd+P and Cd+B indicates 1 mM CdCl₂, 1 mM CdCl₂+5 mM proline and 1 mM CdCl₂+5 mM betaine treatments, respectively. Each value is the mean±SE from four independent experiments. Bars with different letters are significantly different at P < 0.05