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Cadmium uptake and translocation in seedlings of near isogenic lines of durum wheat that differ in grain cadmium accumulation.

Harris NS, Taylor GJ - BMC Plant Biol. (2004)

Bottom Line: In short-term studies (<3 h) using 109Cd-labelled nutrient solutions, there were no differences between lines in time- or concentration-dependent 109Cd accumulation by roots.There were no differences between the lines in 65Zn accumulation or partitioning that could account for the difference between lines in 109Cd translocation.These results suggest that restricted root-to-shoot Cd translocation may limit Cd accumulation in durum wheat grain by directly controlling Cd translocation from roots during grain filling, or by controlling the size of shoot Cd pools that can be remobilised to the grain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada. nsharris@ualberta.ca

ABSTRACT

Background: Cadmium (Cd) concentrations in durum wheat (Triticum turgidum L. var durum) grain grown in North American prairie soils often exceed proposed international trade standards. To understand the physiological processes responsible for elevated Cd accumulation in shoots and grain, Cd uptake and translocation were studied in seedlings of a pair of near-isogenic durum wheat lines, high and low for Cd accumulation in grain.

Results: In short-term studies (<3 h) using 109Cd-labelled nutrient solutions, there were no differences between lines in time- or concentration-dependent 109Cd accumulation by roots. In contrast, rates of 109Cd translocation from roots to shoots following longer exposure (48-60 h) were 1.8-fold higher in the high Cd-accumulating line, despite equal whole-plant 109Cd accumulation in the lines. Over the same period, the 109Cd concentration in root-pressure xylem exudates was 1.7 to 1.9-fold higher in the high Cd-accumulating line. There were no differences between the lines in 65Zn accumulation or partitioning that could account for the difference between lines in 109Cd translocation.

Conclusion: These results suggest that restricted root-to-shoot Cd translocation may limit Cd accumulation in durum wheat grain by directly controlling Cd translocation from roots during grain filling, or by controlling the size of shoot Cd pools that can be remobilised to the grain.

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Long-term 109Cd accumulation in roots of durum wheat seedlings. Time-course of 109Cd accumulation in intact roots (A) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for up to 60 h (solutions changed every 12 h) in 15 mL of complete nutrient solution containing 50 pM 109Cd and 0.5 μM 65Zn. Desorbable 109Cd (B) was removed following treatment by a 30 min (2°C) wash in non-radiolabelled nutrient solution containing 50 μM DTPA. Inset shows desorbable 109Cd expressed as a percentage of total 109Cd accumulation in the roots. Means and standard errors of 7 replicates (3 plants per replicate) are plotted.
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Figure 5: Long-term 109Cd accumulation in roots of durum wheat seedlings. Time-course of 109Cd accumulation in intact roots (A) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for up to 60 h (solutions changed every 12 h) in 15 mL of complete nutrient solution containing 50 pM 109Cd and 0.5 μM 65Zn. Desorbable 109Cd (B) was removed following treatment by a 30 min (2°C) wash in non-radiolabelled nutrient solution containing 50 μM DTPA. Inset shows desorbable 109Cd expressed as a percentage of total 109Cd accumulation in the roots. Means and standard errors of 7 replicates (3 plants per replicate) are plotted.

Mentions: Long-term exposure of seedlings to 109Cd showed that there were differences in Cd partitioning between the two isolines. Time-dependent 109Cd accumulation in desorbed roots was linear up to 60 h (Figure 5A), and TL-L accumulated significantly more 109Cd than TL-H following 24–60 h of continuous exposure (t ≥ 2.09, p < 0.05). The amount of 109Cd desorbed from the roots after 3–12 h (around 0.2 pmol g fresh weight-1, Figure 5B) was similar to the amount desorbed during the short-term studies (Figure 1B). For uptake periods longer than 12 h the amount of 109Cd desorbed from roots declined by approximately 50%, and there were no significant differences between isolines for the amounts or proportions of 109Cd desorbed from the roots (t ≤ 1.82, p > 0.05). Following a 60-h uptake period, desorbable 109Cd accumulation account for less than 1.5% of total 109Cd accumulation in the roots of both isolines (Figure 5B inset). Greater 109Cd accumulation in the roots of TL-L is a result of slower translocation of 109Cd to the shoots in this isoline (Figure 6A) rather than greater uptake by the roots. There was no significant difference between isolines in whole-plant 109Cd accumulation over this period (F1,84 = 0.28, p = 0.601; Figure 6B). The 109Cd concentration in the shoots of TL-H was significantly higher than in the shoots of TL-L for exposure periods greater than 12 h (t ≥ 2.09, p < 0.05). Following a 60-h uptake period, root-to-shoot 109Cd translocation was 1.8-fold higher in TL-H than in TL-L (Table 2).


Cadmium uptake and translocation in seedlings of near isogenic lines of durum wheat that differ in grain cadmium accumulation.

Harris NS, Taylor GJ - BMC Plant Biol. (2004)

Long-term 109Cd accumulation in roots of durum wheat seedlings. Time-course of 109Cd accumulation in intact roots (A) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for up to 60 h (solutions changed every 12 h) in 15 mL of complete nutrient solution containing 50 pM 109Cd and 0.5 μM 65Zn. Desorbable 109Cd (B) was removed following treatment by a 30 min (2°C) wash in non-radiolabelled nutrient solution containing 50 μM DTPA. Inset shows desorbable 109Cd expressed as a percentage of total 109Cd accumulation in the roots. Means and standard errors of 7 replicates (3 plants per replicate) are plotted.
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Related In: Results  -  Collection

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Figure 5: Long-term 109Cd accumulation in roots of durum wheat seedlings. Time-course of 109Cd accumulation in intact roots (A) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for up to 60 h (solutions changed every 12 h) in 15 mL of complete nutrient solution containing 50 pM 109Cd and 0.5 μM 65Zn. Desorbable 109Cd (B) was removed following treatment by a 30 min (2°C) wash in non-radiolabelled nutrient solution containing 50 μM DTPA. Inset shows desorbable 109Cd expressed as a percentage of total 109Cd accumulation in the roots. Means and standard errors of 7 replicates (3 plants per replicate) are plotted.
Mentions: Long-term exposure of seedlings to 109Cd showed that there were differences in Cd partitioning between the two isolines. Time-dependent 109Cd accumulation in desorbed roots was linear up to 60 h (Figure 5A), and TL-L accumulated significantly more 109Cd than TL-H following 24–60 h of continuous exposure (t ≥ 2.09, p < 0.05). The amount of 109Cd desorbed from the roots after 3–12 h (around 0.2 pmol g fresh weight-1, Figure 5B) was similar to the amount desorbed during the short-term studies (Figure 1B). For uptake periods longer than 12 h the amount of 109Cd desorbed from roots declined by approximately 50%, and there were no significant differences between isolines for the amounts or proportions of 109Cd desorbed from the roots (t ≤ 1.82, p > 0.05). Following a 60-h uptake period, desorbable 109Cd accumulation account for less than 1.5% of total 109Cd accumulation in the roots of both isolines (Figure 5B inset). Greater 109Cd accumulation in the roots of TL-L is a result of slower translocation of 109Cd to the shoots in this isoline (Figure 6A) rather than greater uptake by the roots. There was no significant difference between isolines in whole-plant 109Cd accumulation over this period (F1,84 = 0.28, p = 0.601; Figure 6B). The 109Cd concentration in the shoots of TL-H was significantly higher than in the shoots of TL-L for exposure periods greater than 12 h (t ≥ 2.09, p < 0.05). Following a 60-h uptake period, root-to-shoot 109Cd translocation was 1.8-fold higher in TL-H than in TL-L (Table 2).

Bottom Line: In short-term studies (<3 h) using 109Cd-labelled nutrient solutions, there were no differences between lines in time- or concentration-dependent 109Cd accumulation by roots.There were no differences between the lines in 65Zn accumulation or partitioning that could account for the difference between lines in 109Cd translocation.These results suggest that restricted root-to-shoot Cd translocation may limit Cd accumulation in durum wheat grain by directly controlling Cd translocation from roots during grain filling, or by controlling the size of shoot Cd pools that can be remobilised to the grain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada. nsharris@ualberta.ca

ABSTRACT

Background: Cadmium (Cd) concentrations in durum wheat (Triticum turgidum L. var durum) grain grown in North American prairie soils often exceed proposed international trade standards. To understand the physiological processes responsible for elevated Cd accumulation in shoots and grain, Cd uptake and translocation were studied in seedlings of a pair of near-isogenic durum wheat lines, high and low for Cd accumulation in grain.

Results: In short-term studies (<3 h) using 109Cd-labelled nutrient solutions, there were no differences between lines in time- or concentration-dependent 109Cd accumulation by roots. In contrast, rates of 109Cd translocation from roots to shoots following longer exposure (48-60 h) were 1.8-fold higher in the high Cd-accumulating line, despite equal whole-plant 109Cd accumulation in the lines. Over the same period, the 109Cd concentration in root-pressure xylem exudates was 1.7 to 1.9-fold higher in the high Cd-accumulating line. There were no differences between the lines in 65Zn accumulation or partitioning that could account for the difference between lines in 109Cd translocation.

Conclusion: These results suggest that restricted root-to-shoot Cd translocation may limit Cd accumulation in durum wheat grain by directly controlling Cd translocation from roots during grain filling, or by controlling the size of shoot Cd pools that can be remobilised to the grain.

Show MeSH
Related in: MedlinePlus