Abstract
We characterized the absorption and short-term translocation of cadmium (Cd) in rice (Oryza sativa 'Nipponbare') quantitatively using serial images observed with a positron-emitting tracer imaging system. We fed a positron-emitting 107Cd (half-life of 6.5 h) tracer to the hydroponic culture solution and noninvasively obtained serial images of Cd distribution in intact rice plants at the vegetative stage and at the grain-filling stage every 4 min for 36 h. The rates of absorption of Cd by the root were proportional to Cd concentrations in the culture solution within the tested range of 0.05 to 100 nm. It was estimated that the radial transport from the culture to the xylem in the root tissue was completed in less than 10 min. Cd moved up through the shoot organs with velocities of a few centimeters per hour at both stages, which was obviously slower than the bulk flow in the xylem. Finally, Cd arrived at the panicles 7 h after feeding and accumulated there constantly, although no Cd was observed in the leaf blades within the initial 36 h. The nodes exhibited the most intensive Cd accumulation in the shoot at both stages, and Cd transport from the basal nodes to crown root tips was observed at the vegetative stage. We conclude that the nodes are the central organ where xylem-to-phloem transfer takes place and play a pivotal role in the half-day travel of Cd from the soil to the grains at the grain-filling stage.
Highlights
We characterized the absorption and short-term translocation of cadmium (Cd) in rice (Oryza sativa ‘Nipponbare’) quantitatively using serial images observed with a positron-emitting tracer imaging system
Noninvasive Imaging of Cd Movement in an Intact Rice Plant peduncle below the ear reduced Cd translocation to the grain (Riesen and Feller, 2005). These results suggest that the xylem loading and transport is the first rate-controlling step of Cd transition from the soil to the grain in graminaceous plants and the phloem transport and unloading into the grain is the last
Test plants at the vegetative stage were fed with a hydroponic culture solution containing various levels of Cd including radioactive 107Cd and subjected to
Summary
We characterized the absorption and short-term translocation of cadmium (Cd) in rice (Oryza sativa ‘Nipponbare’) quantitatively using serial images observed with a positron-emitting tracer imaging system. We fed a positron-emitting 107Cd (halflife of 6.5 h) tracer to the hydroponic culture solution and noninvasively obtained serial images of Cd distribution in intact rice plants at the vegetative stage and at the grain-filling stage every 4 min for 36 h. It has been demonstrated that xylem loading and transport but not absorption by the roots is one of the rate-controlling steps for Cd accumulation in the grain of graminaceous plants. Noninvasive Imaging of Cd Movement in an Intact Rice Plant peduncle below the ear reduced Cd translocation to the grain (Riesen and Feller, 2005) These results suggest that the xylem loading and transport is the first rate-controlling step of Cd transition from the soil to the grain in graminaceous plants and the phloem transport and unloading into the grain is the last. The second objective of this study was to demonstrate the potential of the latest radiotracer imaging technology for plant physiology
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