Determination of the different components of cadmium short‐term uptake by roots

Abstract

As the various components of the cadmium (Cd) root sink have not been clearly described, there is a need to precisely measure the respective contributions of apoplast and symplast to short‐term root Cd uptake and to explain the linear component of the absorption isotherms. A new method of fractionating Cd in roots was applied to two plant species with contrasting abilities to accumulate Cd: maize (Zea mays) and a Cd‐hyperaccumulating ecotype of alpine pennycress (Noccaea caerulescens). Their roots were exposed for 1 h to increasing concentrations of labeled Cd. Series of desorption baths were used to obtain the root apoplastic Cd in combination with a brief freezing step in liquid nitrogen to separate the intracellular metal from the apoplastic one. The apoplastic uptake accounted for 15% to 82% and for 48% to 96% of the total Cd uptake of maize and of alpine pennycress roots, respectively. In the case of maize, the concentration‐dependent symplastic net flux fitted a biphasic Michaelis‐Menten function, while in the case of alpine pennycress, a Michaelis‐Menten‐plus‐linear function proved a better fit. The second component of the symplastic net flux may reflect absorption through a low‐affinity transport system. Short‐term Cd uptake by roots is dominated by the high‐affinity transport system for exposure concentrations below 1 μM for maize and 0.2 μM for alpine pennycress, while cell‐wall binding prevailed for higher exposure concentrations.

Determining the fluxes of ions (Pb2+, Cu2+ and Cd2+) at the root surface of wetland plants using the scanning ion-selective electrode technique

“…This is consistent with the findings of Ryan et al (1992). The higher influx of Cd 2+ , Cu 2+ and Pb 2+ observed in the roots is possibly dominated by a stronger cell wall sorption (Redjala et al 2009(Redjala et al , 2010. Thus after immobilization of the roots in the measuring solution and equilibration for 10 min, the steady ions fluxes were then recorded across the root tips of the wetland plants.…”

Cadmium uptake kinetics and plants factors of shoot Cd concentration

“…These latter studies, however, have been mostly of short duration of a few hours, so that these results may not be applicable to long term studies as for plants grown in soil. One reason for this is that in short term experiments Cd uptake may be strongly over estimated as a consequence of a rapid Cd accumulation in the apoplasm which is freely accessible to the outer solution (Redjala et al 2010) whereas for Cd uptake into the symplasm the ions have to cross the plasmalemma which is a much slower process. Another reason is that in short term studies of a few hours, in contrast to long term studies, no acclimation of the plants to different Cd levels occurs.…”

Sulfur supply as a sustainable technology for phytoextraction: its effects on cadmium uptake and detoxification in Panicum maximum Jacq. cv. Massai

“…In this regard, Cd uptake (high concentrations) probably is more deeply affected by architecture than by uptake capacity (Vmax and Km) of plant root (REDJALA; MOREL, 2009MOREL, , 2010. This assumption becomes even clearer as we observe the negative correlation between α (Vmax/Km) and biomass production of root system (Table 6) and high Cmin values (Table 4).…”

“…In this context, lowest deposition of suberin (mainly in regions near the Caspary strips) in plants grown with lowest S supply may facilitate the apoplastic transport of Cd to shoots, but this fact can increase the damage caused by Cd (REDJALA; MOREL et al, 2009). Redjala, Sterckeman and Morel (2010) stated that apoplastic uptake of Cd by corn plants ranged from 15 to 82% as a function of increase in Cd concentration, whereas apoplastic uptake of Cd by Massai grass exposed to lowest Cd concentration ranged from 58.5 (0.1 mmol L -1 ) to 67.8% (1.9 mmol L -1 ) as S concentration was increased ( Figure 6).…”

“…In any event, the uptake kinetics of metals normally includes two stages: the first stage is rapid and occurs after contact of metal with roots (passive system -apoplastic uptake), while the second is slowest and depends of metabolic activity (active system -symplastic uptake) (SLOOF; VIRAGH; van der VEER, 1995). However, the importance of each stage varies according to species and concentration of heavy metal and other ions (eg, SO4 2-) in solution (REDJALA; MOREL, 2009MOREL, , 2010.…”