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Pteris vittata is an arsenic (As) hyperaccumulator plant that accumulates a large amount of As into fronds and rhizomes (around 16,000 mg/kg in both after 16 weeks hydroponic cultivation with 30 mg/L arsenate). However, the sequence of long-distance transport of As in this hyperaccumulator plant is unclear. In this study, we used a positron-emitting tracer imaging system (PETIS) for the first time to obtain noninvasive serial images of As behavior in living plants with positron-emitting 74As-labeled tracer. We found that As kept accumulating in rhizomes as in fronds of P. vittata, whereas As was retained in roots of a non-accumulator plant Arabidopsis thaliana. Autoradiograph results of As distribution in P. vittata showed that with low As exposure, As was predominantly accumulated in young fronds and the midrib and rachis of mature fronds. Under high As exposure, As accumulation shifted from young fronds to mature fronds, especially in the margin of pinna, which resulted in necrotic symptoms, turning the marginal color to gray and then brown. Our results indicated that the function of rhizomes in P. vittata was As accumulation and the regulation of As translocation to the mature fronds to protect the young fronds under high As exposure.

Background Positron imaging can be used to non-destructively visualize the dynamics of a positron-emitting radionuclide in vivo, and is therefore a tool for understanding the mechanisms of nutrient transport in intact plants. The transport of zinc, which is one of the most important nutrient elements for plants, has so far been visualized by positron imaging using 62Zn (half-life: 9.2 h), which is manufactured in the limited number of facilities that have a cyclotron. In contrast, the positron-emitting radionuclide 65Zn (half-life: 244 days) is commercially available worldwide. In this study, we examined the possibility of conducting positron imaging of zinc in intact plants using 65Zn. Results By administering 65Zn and imaging over a long time, clear serial images of 65Zn distributions from the root to the panicle of dwarf rice plants were successfully obtained. Conclusions Non-destructive visualization of zinc dynamics in plants was achieved using commercially available 65Zn and a positron imaging system, demonstrating that zinc dynamics can be visualized even in facilities without a cyclotron.

The aims of this study are to investigate whether and how the nitrogen form (nitrate (NO3 (-)) versus ammonium (NH4 (+))) influences cadmium (Cd) uptake and translocation and subsequent Cd phytoextraction by the hyperaccumulator species Sedum plumbizincicola. Plants were grown hydroponically with N supplied as either NO3 (-) or NH4 (+). Short-term (36 h) Cd uptake and translocation were determined innovatively and quantitatively using a positron-emitting Cd-107 tracer and positron-emitting tracer imaging system. The results show that the rates of Cd uptake by roots and transport to the shoots in the NO3 (-) treatment were more rapid than in the NH4 (+) treatment. After uptake for 36 h, 5.6 (0.056 mu M) and 29.0 % (0.290 mu M) of total Cd in the solution was non-absorbable in the NO3 (-) and NH4 (+) treatments, respectively. The local velocity of Cd transport was approximately 1.5-fold higher in roots (3.30 cm h(-1)) and 3.7-fold higher in shoots (10.10 cm h(-1)) of NO3 (-)- than NH4 (+)-fed plants. Autoradiographic analysis of Cd-109 reveals that NO3 (-) nutrition enhanced Cd transportation from the main stem to branches and young leaves. Moreover, NO3 (-) treatment increased Cd, Ca and K concentrations but inhibited Fe and P in the xylem sap. In a 21-day hydroponic culture, shoot biomass and Cd concentration were 1.51 and 2.63 times higher in NO3 (-)- than in NH4 (+)-fed plants. We conclude that compared with NH4 (+), NO3 (-) promoted the major steps in the transport route followed by Cd from solution to shoots in S. plumbizincicola, namely its uptake by roots, xylem loading, root-to-shoot translocation in the xylem and uploading to the leaves. S. plumbizincicola prefers NO3 (-) nutrition to NH4 (+) for Cd phytoextraction.