The drainage of rice soils increases
Cd solubility and results
in high Cd concentrations in rice grains. However, plant Cd uptake
is limited by sorption to iron plaques, and Cd redistribution in the
plant is regulated by the nodes. To better understand the interplay
of Cd uptake and redistribution in rice under drained and flooded
conditions, we determined stable Cd isotope ratios and the expression
of genes coding transporters that can transport Cd into the plant
cells in a pot experiment. In soil, both water management practices
showed similar patterns of isotope variation: the soil solution was
enriched in heavy isotopes, and the root Fe plaque was enriched in
light isotopes. In rice, the leaves were heavier (Δ114/110Cdleaf‑shoot = 0.17 to 0.96‰) and the nodes
were moderately lighter (Δ114/110Cdnode‑shoot = −0.26 to 0.00‰) relative to the shoots under flooded
conditions, indicating preferential retention of light isotopes in
nodes and export of heavy isotopes toward leaves. This is generally
reversed under drained conditions (Δ114/110Cdleaf‑shoot = −0.25 to −0.04‰, Δ114/110Cdnode‑shoot = 0.10 to 0.19‰).
The drained treatment resulted in significantly higher expression
of OsHMA2 and OsLCT1 (phloem loading)
but lower expression of OsHMA3 (vacuolar sequestration)
in nodes and flag leaves relative to the flooded treatment. It appeared
that OsHMA2 and OsLCT1 might preferentially transport isotopically
heavier Cd, and the excess Cd was purposefully retranslocated via
the phloem under drained conditions when the vacuoles could not retain
more Cd. Cd in seeds was isotopically heavier than that in stems under
both water management practices, indicating that heavy isotopes were
preferentially transferred toward seeds via the phloem, leaving light
isotopes retained in stems. These findings demonstrate that the Fe
plaque preferentially adsorbs and occludes light Cd isotopes on the
root surface, and distinct water management practices alter the gene
expression of key transporters in the nodes, which corresponds to
a change in isotope fractionation between shoots and nodes/leaves.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.