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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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Related in: MedlinePlus

109Cd transport in xylem sap of durum wheat seedlings. Time-course of 109Cd concentration in xylem sap (A) and the rate of xylem sap exudation (B) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for between 12 and 60 h in 15 mL of complete nutrient solution containing 25 pM 109Cd (solutions changed every 12 h). Shoots were then excised 5–7 mm above the roots and xylem sap collected for 6 h. Means and standard errors of 10 replicates are plotted.
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Figure 8: 109Cd transport in xylem sap of durum wheat seedlings. Time-course of 109Cd concentration in xylem sap (A) and the rate of xylem sap exudation (B) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for between 12 and 60 h in 15 mL of complete nutrient solution containing 25 pM 109Cd (solutions changed every 12 h). Shoots were then excised 5–7 mm above the roots and xylem sap collected for 6 h. Means and standard errors of 10 replicates are plotted.

Mentions: The time-course of 109Cd concentration in xylem sap root-pressure exudates (Figure 8A) was similar to that of 109Cd accumulation in shoots. The 109Cd concentration in xylem sap increased linearly for up to 60 h, and was significantly higher in TL-H than in TL-L for uptake periods longer than 12 h (t ≥ 2.07, p < 0.05). Following a 60-h uptake period, the 109Cd concentration in xylem sap was 1.9-fold higher in the high Cd-accumulating isoline. The 109Cd concentration in xylem sap was correlated with 109Cd accumulation in the shoots of both isolines (r = 0.863 and 0.705 for TL-H and TL-L, respectively). The rate of sap exudation was consistently higher in TL-H (F1,90 = 33.3, p < 0.001; Figure 8B).


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)

109Cd transport in xylem sap of durum wheat seedlings. Time-course of 109Cd concentration in xylem sap (A) and the rate of xylem sap exudation (B) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for between 12 and 60 h in 15 mL of complete nutrient solution containing 25 pM 109Cd (solutions changed every 12 h). Shoots were then excised 5–7 mm above the roots and xylem sap collected for 6 h. Means and standard errors of 10 replicates are plotted.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC404425&req=5

Figure 8: 109Cd transport in xylem sap of durum wheat seedlings. Time-course of 109Cd concentration in xylem sap (A) and the rate of xylem sap exudation (B) of high (TL-H) and low (TL-L) Cd-accumulating isolines of durum wheat. Roots of 6-d old seedlings were exposed for between 12 and 60 h in 15 mL of complete nutrient solution containing 25 pM 109Cd (solutions changed every 12 h). Shoots were then excised 5–7 mm above the roots and xylem sap collected for 6 h. Means and standard errors of 10 replicates are plotted.
Mentions: The time-course of 109Cd concentration in xylem sap root-pressure exudates (Figure 8A) was similar to that of 109Cd accumulation in shoots. The 109Cd concentration in xylem sap increased linearly for up to 60 h, and was significantly higher in TL-H than in TL-L for uptake periods longer than 12 h (t ≥ 2.07, p < 0.05). Following a 60-h uptake period, the 109Cd concentration in xylem sap was 1.9-fold higher in the high Cd-accumulating isoline. The 109Cd concentration in xylem sap was correlated with 109Cd accumulation in the shoots of both isolines (r = 0.863 and 0.705 for TL-H and TL-L, respectively). The rate of sap exudation was consistently higher in TL-H (F1,90 = 33.3, p < 0.001; Figure 8B).

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