Arsenite transport into paddy rice (Oryza sativa) roots

Abstract

Summary• Here the mechanism of arsenite transport into paddy rice ( Oryza sativa ) roots, uptake of which is described by Michaelis-Menten kinetics, is reported. A recent study on yeast ( Saccharomyces cerevisiae ) showed that undissociated arsenite (its pK a is 9.2) was transported across the plasma membrane via a glycerol transporting channel. To investigate whether the same mechanism of transport was involved for rice, competitive studies with glycerol, which is transported into cells via aquaporins, were performed.• Glycerol competed with arsenite for transport in a dose-dependent manner, indicating that arsenite and glycerol uptake mechanisms were the same. Arsenate transport was unaffected by glycerol, confirming that arsenate and arsenite are taken up into cells by different mechanisms.• Antimonite, an arsenite analogue that is transported into S. cerevisiae cells by aquaporins, also competed with arsenite transport in a dose-dependent manner, providing further evidence that arsenite is transported into rice roots via glycerol transporting channels. Mercury (Hg 2+ ) inhibited both arsenite and arsenate uptake, suggesting that inhibition of influx was due to general cellular stress rather than the specific action of Hg 2+ on aquaporins.• Arsenite uptake by pea ( Pisum sativum ) and wheat ( Triticum aestivum ) was also described by Michaelis-Menten kinetics.

Uptake of oxytetracycline and its phytotoxicity to alfalfa (Medicago sativa L.)

“…Our findings showed that glycerol and Ag þ did not compete with OTC for uptake and transport into alfalfa roots, suggesting that OTC does not enter into the root through water channels. The glycerol concentration of 10 mM used in the present study was high enough to inhibit arsenite uptake by rice within 20 min, which is sufficient for the inhibition of aquaporins (Meharg and Jardine, 2003), and the 5 mM of Ag þ was also suitable (Niemietz and Tyerman, 2002). Therefore, our data convincingly demonstrated that OTC uptake was aquaporins-independent.…”

“…OTC uptake by alfalfa roots was decreased when exposed to 0.01 and 0.1 mM Hg 2þ compared with the control (Table 1). However, the reduction in OTC uptake after the addition of Hg 2þ could be due to general disruption of plasma membrane biochemistry caused by the highly toxic Hg 2þ ion (Dordas and Brown, 2001;Martre et al, 2001;Du et al, 2005), rather than specific inhibition of aquaporins (Meharg and Jardine, 2003). To further elucidate the possible role of aquaporins in OTC uptake, we used the other competitors, such as glycerol and Ag þ .…”

“…Experiment 5: OTC uptake influenced by metabolic and aquaporin inhibitors OTC uptake was investigated using the procedure described elsewhere (Meharg and Jardine, 2003;Liang et al, 2005). The metabolic inhibitor, 2,4-DNP, was added at a concentration of 1 mM to suppress the uptake of OTC.…”

Is the effect of silicon on rice uptake of arsenate (AsV) related to internal silicon concentrations, iron plaque and phosphate nutrition?

“…The addition of Si to the pretreatment or uptake solution significantly decreased shoot and root As concentrations, suggesting that both external and internal Si could affect As uptake. The kinetics study showed that in the treatment without Si the uptake kinetics were similar to those obtained by Meharg and Jardine (2003) and Chen et al (2005). Uptake of As by rice roots was significantly influenced by ÀSi þ Si treatment (Table 3).…”

“…Roots were excised and incubated in deionized water for 20 min at room temperature and were then transferred to conical flasks containing 1000 ml test solution, and incubated for further 30 min according to Meharg and Jardine (2003) and Chen et al (2005). The test solutions with different concentrations of As were 1.5, 3.0, 7.5, 15.0, 30.0 and 75.0 mM.…”