Bioaccumulation of the Heavy Metal Cadmium and Its Tolerance Mechanisms in Experimental Plant Suaeda salsa

Abstract

Suaeda salsa is relatively tolerant to cadmium (Cd) contamination. In order to investigate the bioaccumulation and stress responses of S. salsa under chronic exposure, we explored the growth, accumulation, and changes in antioxidant enzymes and glutathione (GSH) under different Cd concentrations over a 30-day soil culture experiment. Seedling height and weight in the 13.16 mg/kg Cd group were 13.26 cm and 0.21 g, significantly higher than the control group. Growth was significantly inhibited under high Cd concentration exposure, with a seedling and root length of 9.65 cm and 3.77 cm. The Cd concentration in all tissues was positively related to Cd treatment concentration, with the Cd contents in the roots being higher than in the other tissues. At a subcellular level, Cd was mainly concentrated in the cell walls, organelles, and soluble components within the range of 0.05-8.29, 0.02-2.40 and 0.08-1.35 μg/g, respectively. The accumulation of Cd in the roots tracked its proportion in the cell walls. The malondialdehyde (MDA) content of the plant tissues increased with increasing Cd concentration, indicating that Cd stress caused oxidative damage. The GSH content increased with increasing Cd concentration, with maximum values of 0.515 μmol/g in the stem in the 66.07 mg/kg Cd group. The catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activity showed different change trends under Cd exposure. The results in this study could provide useful information on the tolerance mechanism of Cd in S. salsa, which provides information for exploiting S. salsa as a candidate for phytoremediation of Cd contamination.

Keywords: Suaeda salsa; antioxidative enzyme; cadmium content; plant growth; subcellular distribution.

Figure 1

Accumulation characteristics of Cadmium (Cd) in the roots, stems, and leaves of S. salsa. The different letters represent the significant difference among different concentrations in each tissue (p < 0.05), N = 3.

Figure 2

Cd subcellular distribution in the roots (a), stems (b), and leaves (c) of S.salsa. The different letters represent the significant difference among various subcellular fractions (p < 0.05), N = 3.

Figure 3

Subcellular proportion of Cd in different tissues of S. salsa.

Figure 4

The change of antioxidative enzyme in S. salsa under Cd exposure. (a) represents the change in malondialdehyde (MDA) Content; (b) represents the change of peroxidase (POD) activity; (c) represents the change of superoxide dismutase (SOD) activity; (d) represents the change of catalase (CAT) activity. The different letters represent the significant difference among Cd concentrations in each tissue (p < 0.05), N = 3.

Figure 5

The change of glutathione (GSH) content in S. salsa under Cd exposure. The different letters represent the significant difference among concentrations (p < 0.05), N = 3.

Figure 6

The score and loading of principal component analysis (PCA) on the set of plant morphological data under Cd exposure. (a) represents the correlation among variables along two PCA axes (PC1 × PC2); (b) represents ordination of case along two PCA axes (PC1 × PC2).