Evidence for separate translocation pathways in determining cadmium accumulation in grain and aerial plant parts in rice.
BACKGROUND
Cadmium (Cd) translocation and accumulation in the grain and aerial plant parts of rice (Oryza sativa L.) is an important aspect of food safety and phytoextraction in areas with contaminated soil. Because control of Cd translocation and accumulation is likely to be determined by the plants genetics, the Cd contents of grain and the aerial parts of rice may be manipulated to improve food safety and for phytoextraction ability. This study studied Cd translocation and accumulation and their genetic control in aerial parts of rice to provide a starting point for improving food safety and phytoextraction in Cd-contaminated soils.


RESULTS
In the japonica rice cultivar "Nipponbare", Cd accumulated in leaves and culms until heading, and in culms and ears after heading. Two quantitative trait loci (QTLs) from indica cv. "Kasalath", qcd4-1 and qcd4-2, affect Cd concentrations in upper plant parts just before heading. Three near-isogenic lines (NILs) with qcd4-1 and qcd4-2 were selected from the "Nipponbare" background, and were analyzed for the effects of each QTL, and for interactions between the two QTLs. From the results compared between "Nipponbare" and each NIL, neither QTL influenced total Cd accumulation in aerial parts at 5 days after heading, but the interaction between two QTLs increased Cd accumulation. At 35 days after heading, qcd4-2 had increased Cd accumulation in the aerial plant parts and decreased translocation from leaves other than flag leaf, but interaction between the two QTLs increased translocation from leaves. NILqcd4-1,2 accumulated higher concentrations of Cd in brown rice than "Nipponbare".


CONCLUSIONS
Three types of Cd translocation and accumulation patterns demonstrated by NILs suggested that the accumulation of Cd in leaves and culms before heading, and translocation from them after heading are responsible for Cd accumulation in grain. Cd translocation from roots to culms and ears after heading may direct Cd to the aerial organs without influencing brown rice accumulation.
Kashiwagi
Takayuki
T
National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan. kassy@nias.affrc.go.jp
Shindoh
Kumiko
K
Hirotsu
Naoki
N
Ishimaru
Ken
K
D001692:Biological Transport; D002104:Cadmium / Q000378:metabolism*; D003433:Crosses, Genetic; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D035261:Plant Components, Aerial / Q000378:metabolism*; D040641:Quantitative Trait Loci; D012989:Soil Pollutants / Q000378:metabolism
D012989:Soil Pollutants; D002104:Cadmium