Abstract
BACKGROUND: Among cereals, rice has a genetic propensity to accumulate high levels of cadmium (Cd) in grains. Xylem-mediated root-to-shoot translocation rather than root uptake has been suggested as the main physiological factor accounting for the genotypic variation observed in Cd accumulation in shoots and grains. Several evidence indicate OsHMA2 - a putative zinc (Zn) transporter - as the main candidate protein that could be involved in mediating Cd- and Zn-xylem loading in rice. However, the specific interactions between Zn and Cd in rice often appear anomalous if compared to those observed in other staple crops, suggesting that root-to-shoot Cd translocation process could be more complex than previously thought. In this study we performed a complete set of competition experiments with Zn and Cd in order to analyze their possible interactions and reciprocal effects at the root-to-shoot translocation level. RESULTS: The competition analysis revealed the lack of a full reciprocity when considering the effect of Cd on Zn accumulation, and vice versa, since the accumulation of Zn in the shoots was progressively inhibited by Cd increases, whereas that of Cd was only partially impaired by Zn. Such behaviors were probably dependent on Cd-xylem loading mechanisms, as suggested by: i) the analysis of Zn and Cd content in the xylem sap performed in relation to the concentration of the two metals in the mobile fractions of the roots; ii) the analysis of the systemic movement of (107)Cd in short term experiments performed using a positron-emitting tracer imaging system (PETIS). CONCLUSIONS: Our results suggest that at least two pathways may mediate root-to-shoot Cd translocation in rice. The former could involve OsHMA2 as Zn(2+)/Cd(2+) xylem loader, whereas the latter appears to involve a Zn-insensitive system that still needs to be identified.
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Claims 5
Claim · model-written summary
Increasing Cd progressively inhibited Zn accumulation in rice shoots.
- Taxon
- rice
Oryza sativat0 - Treatment
- Cd increasese0
- Outcome
- accumulation of Zn in the shootse0
- Direction
- inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the accumulation of Zn in the shoots was progressively inhibited by Cd increases”
t0“Rice”
Claim · model-written summary
Zn only partially impaired Cd accumulation in rice shoots.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“whereas that of Cd was only partially impaired by Zn”
t0“Rice”
Claim · model-written summary
The authors suggest that at least two pathways mediate root-to-shoot Cd translocation in rice.
- Taxon
- riceOryza sativae0
- Outcome
- root-to-shoot Cd translocatione0
- Qualifier
- at least two pathwayse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Our results suggest that at least two pathways may mediate root-to-shoot Cd translocation in rice.”
t0“Rice”
Claim · model-written summary
One proposed rice Cd translocation pathway could use OsHMA2 as a Zn and Cd xylem loader.
- Taxon
- riceOryza sativat0
- Gene
- OsHMA2e0
- Outcome
- Zn(2+)/Cd(2+) xylem loadere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The former could involve OsHMA2 as Zn(2+)/Cd(2+) xylem loader”
t0“Rice”
Claim · model-written summary
A second proposed rice Cd translocation pathway appears Zn-insensitive.
- Taxon
- riceOryza sativat0
- Outcome
- Zn-insensitive systeme0
- Qualifier
- still needs to be identifiede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the latter appears to involve a Zn-insensitive system that still needs to be identified”
t0“Rice”
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