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The Density and Length of Root Hairs Are Enhanced in Response to Cadmium and Arsenic by Modulating Gene Expressions Involved in Fate Determination and Morphogenesis of Root Hairs in Arabidopsis

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ABSTRACT

Root hairs are tubular outgrowths that originate from epidermal cells. Exposure of Arabidopsis to cadmium (Cd) and arsenic [arsenite, As(III)] increases root hair density and length. To examine the underlying mechanism, we measured the expression of genes involved in fate determination and morphogenesis of root hairs. Cd and As(III) downregulated TTG1 and GL2 (negative regulators of fate determination) and upregulated GEM (positive regulator), suggesting that root hair fate determination is stimulated by Cd and As(III). Cd and As(III) increased the transcript levels of genes involved in root hair initiation (RHD6 and AXR2) and root hair elongation (AUX1, AXR1, ETR1, and EIN2) except CTR1. DR5::GUS transgenic Arabidopsis showed a higher DR5 expression in the root tip, suggesting that Cd and As(III) increased the auxin content in the root tip. Knockdown of TTG1 in Arabidopsis resulted in increased root hair density and decreased root hair length compared with the control (Col-0) on 1/2 MS media. This phenotype may be attributed to the downregulation of GL2 and CTR1 and upregulation of RHD6. By contrast, gem mutant plants displayed a decrease in root hair density and length with reduced expression of RHD6, AXR2, AUX1, AXR1, ETR1, CTR1, and EIN2. Taken together, our results indicate that fate determination, initiation, and elongation of root hairs are stimulated in response to Cd and As(III) through the modulation of the expression of genes involved in these processes in Arabidopsis.

No MeSH data available.


Effect of Cd and As(III) on the length and density of root hairs in Arabidopsis.(A) Root hair morphology of Arabidopsis Col-0 seedlings germinated and grown for a week on 1/2 MS agar media treated with no metal, 20, 40 μM CdSO4, and 5, 10, 30 μM As(III). Roots were observed at 40× magnification; scale bars = 0.2 mm. Photographs show plants representative of the 10 plants examined in each experiment. (B) Density and length of root hair treated with Cd shown in (A). Root hair density was expressed as the number counted in a 5 mm section from the starting point of differentiation zone under a microscope. Root hair length was measured in a 5 mm section of differentiation zone. Root hairs were photographed with Leica Stereoscopic microscope (MZ10F, Germany), and their length was quantified using Image J software as described in Materials and methods. Values are average (±SE) of three independent experiments, each involving 10 seedlings. (C) Density and length of root hairs treated with As(III) shown in (A). Root hair density and length were measured as in (B). Different letters in each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
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Figure 2: Effect of Cd and As(III) on the length and density of root hairs in Arabidopsis.(A) Root hair morphology of Arabidopsis Col-0 seedlings germinated and grown for a week on 1/2 MS agar media treated with no metal, 20, 40 μM CdSO4, and 5, 10, 30 μM As(III). Roots were observed at 40× magnification; scale bars = 0.2 mm. Photographs show plants representative of the 10 plants examined in each experiment. (B) Density and length of root hair treated with Cd shown in (A). Root hair density was expressed as the number counted in a 5 mm section from the starting point of differentiation zone under a microscope. Root hair length was measured in a 5 mm section of differentiation zone. Root hairs were photographed with Leica Stereoscopic microscope (MZ10F, Germany), and their length was quantified using Image J software as described in Materials and methods. Values are average (±SE) of three independent experiments, each involving 10 seedlings. (C) Density and length of root hairs treated with As(III) shown in (A). Root hair density and length were measured as in (B). Different letters in each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).

Mentions: Arabidopsis plants grown on 1/2 MS agar medium containing Cd (CdSO4, 40 μM) and AsIII (AsNaO2, 10 μM) for 1 week showed a 50% decrease in primary root length (Figures 1A,B). By contrast, root hair length and density increased significantly in Arabidopsis plants exposed to Cd and As(III) compared with those in control plants (Figure 2A). Exposure to Cd at 20 and 40 μM increased the number of root hairs in a 5 mm section from the starting point of the root differentiation zone by 22 and 50%, respectively, compared with control plants (Figure 2B). Root hair number and length could not be measured at 60 μM Cd because germination was completely inhibited (data not shown). As(III) treatment increased the number of root hairs by 23% at 5 μM, 39% at 10 μM, and 19% at 30 μM (Figure 2C). Cd-treated plants showed an increase in root hair length of 38% at 20 μM and 77% at 40 μM compared with that of the control (1/2 MS) (Figure 2B). As(III) treatment also increased root hair length by 32% at 5 μM, 63% at 10 μM, and 62% at 30 μM (Figure 2C).


The Density and Length of Root Hairs Are Enhanced in Response to Cadmium and Arsenic by Modulating Gene Expressions Involved in Fate Determination and Morphogenesis of Root Hairs in Arabidopsis
Effect of Cd and As(III) on the length and density of root hairs in Arabidopsis.(A) Root hair morphology of Arabidopsis Col-0 seedlings germinated and grown for a week on 1/2 MS agar media treated with no metal, 20, 40 μM CdSO4, and 5, 10, 30 μM As(III). Roots were observed at 40× magnification; scale bars = 0.2 mm. Photographs show plants representative of the 10 plants examined in each experiment. (B) Density and length of root hair treated with Cd shown in (A). Root hair density was expressed as the number counted in a 5 mm section from the starting point of differentiation zone under a microscope. Root hair length was measured in a 5 mm section of differentiation zone. Root hairs were photographed with Leica Stereoscopic microscope (MZ10F, Germany), and their length was quantified using Image J software as described in Materials and methods. Values are average (±SE) of three independent experiments, each involving 10 seedlings. (C) Density and length of root hairs treated with As(III) shown in (A). Root hair density and length were measured as in (B). Different letters in each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
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Figure 2: Effect of Cd and As(III) on the length and density of root hairs in Arabidopsis.(A) Root hair morphology of Arabidopsis Col-0 seedlings germinated and grown for a week on 1/2 MS agar media treated with no metal, 20, 40 μM CdSO4, and 5, 10, 30 μM As(III). Roots were observed at 40× magnification; scale bars = 0.2 mm. Photographs show plants representative of the 10 plants examined in each experiment. (B) Density and length of root hair treated with Cd shown in (A). Root hair density was expressed as the number counted in a 5 mm section from the starting point of differentiation zone under a microscope. Root hair length was measured in a 5 mm section of differentiation zone. Root hairs were photographed with Leica Stereoscopic microscope (MZ10F, Germany), and their length was quantified using Image J software as described in Materials and methods. Values are average (±SE) of three independent experiments, each involving 10 seedlings. (C) Density and length of root hairs treated with As(III) shown in (A). Root hair density and length were measured as in (B). Different letters in each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
Mentions: Arabidopsis plants grown on 1/2 MS agar medium containing Cd (CdSO4, 40 μM) and AsIII (AsNaO2, 10 μM) for 1 week showed a 50% decrease in primary root length (Figures 1A,B). By contrast, root hair length and density increased significantly in Arabidopsis plants exposed to Cd and As(III) compared with those in control plants (Figure 2A). Exposure to Cd at 20 and 40 μM increased the number of root hairs in a 5 mm section from the starting point of the root differentiation zone by 22 and 50%, respectively, compared with control plants (Figure 2B). Root hair number and length could not be measured at 60 μM Cd because germination was completely inhibited (data not shown). As(III) treatment increased the number of root hairs by 23% at 5 μM, 39% at 10 μM, and 19% at 30 μM (Figure 2C). Cd-treated plants showed an increase in root hair length of 38% at 20 μM and 77% at 40 μM compared with that of the control (1/2 MS) (Figure 2B). As(III) treatment also increased root hair length by 32% at 5 μM, 63% at 10 μM, and 62% at 30 μM (Figure 2C).

View Article: PubMed Central - PubMed

ABSTRACT

Root hairs are tubular outgrowths that originate from epidermal cells. Exposure of Arabidopsis to cadmium (Cd) and arsenic [arsenite, As(III)] increases root hair density and length. To examine the underlying mechanism, we measured the expression of genes involved in fate determination and morphogenesis of root hairs. Cd and As(III) downregulated TTG1 and GL2 (negative regulators of fate determination) and upregulated GEM (positive regulator), suggesting that root hair fate determination is stimulated by Cd and As(III). Cd and As(III) increased the transcript levels of genes involved in root hair initiation (RHD6 and AXR2) and root hair elongation (AUX1, AXR1, ETR1, and EIN2) except CTR1. DR5::GUS transgenic Arabidopsis showed a higher DR5 expression in the root tip, suggesting that Cd and As(III) increased the auxin content in the root tip. Knockdown of TTG1 in Arabidopsis resulted in increased root hair density and decreased root hair length compared with the control (Col-0) on 1/2 MS media. This phenotype may be attributed to the downregulation of GL2 and CTR1 and upregulation of RHD6. By contrast, gem mutant plants displayed a decrease in root hair density and length with reduced expression of RHD6, AXR2, AUX1, AXR1, ETR1, CTR1, and EIN2. Taken together, our results indicate that fate determination, initiation, and elongation of root hairs are stimulated in response to Cd and As(III) through the modulation of the expression of genes involved in these processes in Arabidopsis.

No MeSH data available.