Do Antimonite and Silicon Share the Same Root Uptake Pathway by Lsi1 in Sorghum bicolor L. Moench?

Abstract

A study was conducted to further develop our understanding of antimony (Sb) uptake in plants. Unlike other metal(loid)s, such as silicon (Si), the mechanisms of Sb uptake are not well understood. However, SbIII is thought to enter the cell via aquaglyceroporins. We investigated if the channel protein Lsi1, which aids in Si uptake, also plays a role in Sb uptake. Seedlings of WT sorghum, with normal silicon accumulation, and its mutant (sblsi1), with low silicon accumulation, were grown in Hoagland solution for 22 days in the growth chamber under controlled conditions. Control, Sb (10 mg Sb L^-1), Si (1mM) and Sb + Si (10 mg Sb L^-1 + 1 mM Si) were the treatments. After 22 days, root and shoot biomass, the concentration of elements in root and shoot tissues, lipid peroxidation and ascorbate levels, and relative expression of Lsi1 were determined. When mutant plants were exposed to Sb, they showed almost no toxicity symptoms compared to WT plants, indicating that Sb was not toxic to mutant plants. On the other hand, WT plants had decreased root and shoot biomass, increased MDA content and increased Sb uptake compared to mutant plants. In the presence of Sb, we also found that SbLsi1 was downregulated in the roots of WT plants. The results of this experiment support the role of Lsi1 in Sb uptake in sorghum plants.

Keywords: Lsi1 transporter; antimony (Sb); ascorbate; malondialdehyde; metalloid uptake pathway; silicon (Si) accumulation.

Figure 1

Picture taken 22 DAP (days after planting) depicting the plant growth of the sorghum wild-type (W) and sblsi1 mutant (M) plants grown under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹ + 1 mM Si) (Scale bar: 20 cm).

Figure 2

Root fresh weight (a), root dry weight (b), shoot fresh weight (c) and shoot dry weight (d) in the sorghum wild-type (W) and sblsi1 mutant (M) plants grown under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹ + 1 mM Si). Values are means ± SD (n = 3). Different letters indicate significant differences between the treatments at p < 0.05.

Figure 3

Malondialdehyde (MDA) contents in roots (a) and shoots (b) in sorghum wild-type (W) and sblsi1 mutant (M) plants grown under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹ + 1 mM Si). Values are means ± SD (n = 3). Different letters indicate significant differences between the treatments at p < 0.05.

Figure 4

Ascorbate (AsA) content in roots of sorghum wild-type (W) and sblsi1 mutant (M) plants grown under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹+ 1 mM Si). Values are means ± SD (n = 3). Different letters indicate significant differences between the treatments at p < 0.05.

Figure 5

Concentration of Si in roots (a) and shoots (b); and concentration of Sb in roots (c) and shoots (d) in sorghum wild-type (W) and sblsi1 mutant (M) plants grown under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹ + 1 mM Si). Values are means ± SD (n = 3). Different letters indicate significant differences between the treatments at p < 0.05.

Figure 6

Relative normalized expression of SbLsi1 in roots of wild-type sorghum plants (a) 5 DAP and (b) 22 DAP under treatments: C (Control), Sb (10 mg Sb L⁻¹), Si (1 mM) and Sb + Si (10 mg Sb L⁻¹ + 1 mM Si). Gene expression for the control was set as 1.0. Statistically significant differences between control and treated plants were analyzed via Student’s t test (p < 0.05) and are denoted as *. Values are means ± standard deviation. The mean values are based on three technical and three biological replicates.