Changes in Growth and Heavy Metal and Phenolic Compound Accumulation in Buddleja cordata Cell Suspension Culture under Cu, Fe, Mn, and Zn Enrichment

Abstract

Buddleja cordata cell suspension cultures could be used as a tool for investigating the capabilities of this species to tolerate heavy metals (HMs) and for assessing the effects of HMs on the accumulation of phenolic compounds in this species. It grows in a wide range of habitats in Mexico, including ultramafic soils, and mobilizes some HMs in the soil. The mobilization of these HMs has been associated with phenolic substances. In addition, this species is used in Mexican traditional medicine. In the present study, a B. cordata cell suspension culture was grown for 18 days in a culture medium enriched with Cu (0.03-0.25 mM), Fe (0.25-1.5 mM), Mn (0.5-3.0 mM), or Zn (0.5-2.0 mM) to determine the effects of these HMs on growth and HM accumulation. We also assessed the effects of the HMs on phenolic compound accumulation after 1 and 18 days of HM exposure. Cells were able to grow at almost all tested HM concentrations and accumulated significant amounts of each HM. The highest accumulation levels were as follows: 1160 mg Cu kg^-1, 6845 mg Fe kg^-1, 3770 mg Mn kg^-1, and 6581 mg Zn kg^-1. Phenolic compound accumulation was affected by the HM exposure time and corresponded to each HM and its concentration. Future research should analyze whole plants to determine the capabilities of Buddleja cordata to accumulate abnormally high amounts of HM and to evaluate the physiological impact of changes in the accumulation of phenolic compounds.

Keywords: elicitation; heavy metal tolerance; secondary metabolite; verbascoside.

Figure 1

Effects of (a) Cu, (b) Fe, (c) Mn, and (d) Zn at different concentrations on the growth tolerance index of the B. cordata cell suspension culture grown for 18 days in the culture medium enriched with heavy metals. All results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level.

Figure 1

Effects of (a) Cu, (b) Fe, (c) Mn, and (d) Zn at different concentrations on the growth tolerance index of the B. cordata cell suspension culture grown for 18 days in the culture medium enriched with heavy metals. All results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level.

Figure 2

Heavy metal accumulation and bioaccumulation factors of Cu, Fe, Mn, and Zn in the B. cordata cell suspension grown for 18 days in a culture medium enriched with the heavy metals at different concentrations: (a) 0.03 to 0.25 mM Cu; (b) 0.25 to 1.5 mM Fe; (c) 0.5 to 3.0 mM Mn; and (d) 0.5 to 2.0 mM Zn. The concentrations of the heavy metals in the control treatment were 0.00005 mM Cu, 0.05 mM Fe, 0.05 mM Mn, and 0.015 mM Zn. All the results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level for a particular response variable.

Figure 2

Heavy metal accumulation and bioaccumulation factors of Cu, Fe, Mn, and Zn in the B. cordata cell suspension grown for 18 days in a culture medium enriched with the heavy metals at different concentrations: (a) 0.03 to 0.25 mM Cu; (b) 0.25 to 1.5 mM Fe; (c) 0.5 to 3.0 mM Mn; and (d) 0.5 to 2.0 mM Zn. The concentrations of the heavy metals in the control treatment were 0.00005 mM Cu, 0.05 mM Fe, 0.05 mM Mn, and 0.015 mM Zn. All the results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level for a particular response variable.

Figure 2

Heavy metal accumulation and bioaccumulation factors of Cu, Fe, Mn, and Zn in the B. cordata cell suspension grown for 18 days in a culture medium enriched with the heavy metals at different concentrations: (a) 0.03 to 0.25 mM Cu; (b) 0.25 to 1.5 mM Fe; (c) 0.5 to 3.0 mM Mn; and (d) 0.5 to 2.0 mM Zn. The concentrations of the heavy metals in the control treatment were 0.00005 mM Cu, 0.05 mM Fe, 0.05 mM Mn, and 0.015 mM Zn. All the results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level for a particular response variable.

Figure 3

Phenolic compound accumulation (total phenolic and verbascoside contents) in the B. cordata cell suspension culture grown for 18 and 1 day(s) in a culture medium enriched with heavy metals at different concentrations. At 18 and 1 day(s): (a,e) 0.03 to 0.25 mM Cu; (b,f) 0.25 to 1.5 mM Fe; (c,g) 0.5 to 3.0 mM Mn; and (d,h) 0.5 to 2.0 mM Zn. The concentrations of heavy metals in the control treatment were 0.00005 mM Cu, 0.05 mM Fe, 0.05 mM Mn, and 0.015 mM Zn. All results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level for a particular response variable.

Figure 3

Phenolic compound accumulation (total phenolic and verbascoside contents) in the B. cordata cell suspension culture grown for 18 and 1 day(s) in a culture medium enriched with heavy metals at different concentrations. At 18 and 1 day(s): (a,e) 0.03 to 0.25 mM Cu; (b,f) 0.25 to 1.5 mM Fe; (c,g) 0.5 to 3.0 mM Mn; and (d,h) 0.5 to 2.0 mM Zn. The concentrations of heavy metals in the control treatment were 0.00005 mM Cu, 0.05 mM Fe, 0.05 mM Mn, and 0.015 mM Zn. All results are shown as the mean ± SD. The same lowercase letter indicates no significant difference at a 5% significance level for a particular response variable.